Full transcript
0:01continue with Chapter two we have a few
0:06more concepts to go over one more big
0:09formula that I know of absolute to that
0:14we're gonna run over real quick before
0:17the period and then we'll have our last
0:19today so just taking attendance tonight
0:23at Emily who sits next to Akira she's
0:27here
0:30Morgan old Kendra sits there and Jamie
0:37and both of them are here too
0:39Hannah's here Hannah did you move up a
0:42spot no so there's really only six
0:50people in this class that doesn't sound
0:52right
0:53Kayla was missed like three weeks that's
1:00really missing any more than that thanks
1:05for helping alright so today acoustic
1:20velocity is we know by now that the
1:22average of soft-tissue is fifteen forty
1:25meters per second but if you actually
1:26look at the individual velocities of
1:28everything inside the human body there's
1:30hardly anything within the human body
1:32that actually is fifteen forty meters
1:35per second it's around fifteen forty
1:38meters so there's like 15 60 meters per
1:40second or fifteen thirty or fifteen
1:42hundred so there's nothing that really
1:46travels at exactly at fifteen forty
1:48meters per second but the composite of
1:50all them together comes up to about
1:51fifteen forty meters per second for soft
1:53tissue the other thing that's very
1:55interesting is that a lot of fluids in
1:57the body including urine bile blood all
2:03of these travel somewhere around 1,500
2:06meters per second as well or close to 15
2:0840 meters per second per second the more
2:10viscous the fluid like water postures
2:13thicker things
2:14they tend to travel at different speeds
2:17as well
2:18so it's very possible that you would
2:20have a fluid that also travels at 15 40
2:23meters per second then the reason why I
2:25bring up this concept is because I
2:27remember there's a question it's either
2:29on your midterm or next test that says
2:33if a medium travels at fifteen forty
2:36meters per second that means a it is
2:40soft-tissue be it maybe soft tissue or C
2:45it can't be soft tissue what's the
2:48correct answer to that good feedback yep
2:54good I'm hearing it it's a maybe soft
2:58tissue maybe fluid it may be other
3:00things as well
3:01so it doesn't mean it must be soft
3:04tissue because clearly nothing exactly
3:06travels at fifteen forty meters per
3:07second but yes it may be soft tissue
3:11okay so other common velocities that we
3:15will deal with last week in your lab you
3:17look at the velocity in air air exists
3:20and lungs
3:21it exists in your intestinal tract it
3:24exists inside of abscesses inside the
3:27body so air travels roughly around 330
3:32meters per second yes you can find
3:34different velocities in your textbooks
3:36but it's all related to temperature so
3:38at different temperatures that slightly
3:41travels differently another common one
3:44is bone and that travels at 4080 that's
3:49400 800 meters per second these are ones
3:55that you should know as well as you know
3:5715 40 meters per second so what
4:01determines the acoustic velocity of a
4:03particular medium do we cover this last
4:09week no okay thank you so there are four
4:14media characteristics that determine how
4:17fast or how well a potato meal is going
4:21to propagate sound it
4:26it's important to know that your your
4:29book uses the terms propagation speed
4:33acoustic velocity or the ability to
4:37propagate energy they use these phrases
4:40all interchangeably so if a medium
4:44propagates energy well it also has high
4:46propagation speed or high acoustic
4:48velocity that make sense okay good all
4:52right so I actually want to skip the
4:54first one I actually have listed here
4:56elasticity because it's like one of the
4:59least important ones of all of them the
5:04most important one is the one that's
5:06listed last which is alt modulus or what
5:12we call stiffness stiffnesses to explain
5:19it is how resistant a particular object
5:22is to change so if you think of a block
5:26of steel it's doesn't want to change its
5:29shape very well and if it does change
5:31its shape it doesn't really bounce back
5:33to its original shape very well so
5:36something that has high bulk modulus is
5:40something that is extremely stiff this
5:43is the most important factor in
5:45determining acoustic velocity so if you
5:49have a stiff medium or a medium that has
5:52high bulk modules it propagates energy
5:55well you come back so high bulk modulus
6:00or high stiffness mediums propagate
6:02energy well how do we know this well we
6:04know that Native Americans listen with
6:06their ear to the ground
6:07- listen buffalo from miles away right
6:10we know that well you probably kids
6:14probably don't do this but before video
6:16games and kids had to get out and play
6:19and do something interesting we used to
6:20play around train tracks you could put
6:24your ear to a train track and hear a
6:25train like 30 40 miles away because the
6:29train tracks are steel they propagate
6:32energy well so
6:36stiff objects will allow you to
6:40propagate even the smallest amount of
6:43energy to give an example let's just say
6:46for example I asked you all to turn your
6:49heads and put your ears flat on the
6:52surface of these desks right and so much
6:57so that you can actually feel the
6:58suction of your your your ear rate on
7:01the right down the desk itself and then
7:04I'm going to come by and here hit it
7:06with a hammer would you feel that not
7:08that I'm hitting you with a hammer but
7:10I'm just simply hitting the table with a
7:11hammer it would be pretty painful for
7:14you to absorb that kind of energy and
7:16something so sensitive is your ear right
7:17that's because the table propagated
7:20energy well now let's do the opposite
7:22I'll have you put not the opposite but
7:24something different now I'm going to
7:26have you put a thick piece of carpet on
7:28your desk and then put your head down
7:31and I'm gonna do the same thing you
7:34would probably hear the thumb only from
7:36the table not actually from the carpet
7:39itself so why is that because the carpet
7:42is not stiff the carbon is actually
7:45dense the carpet is what you would call
7:49soft or perhaps lacking elasticity the
7:54ability to bounce back to its original
7:55shape more like a beanbag and less like
7:58a tennis ball you would say that a
8:01tennis ball has high elasticity because
8:03when you compress it it bounces right
8:04back to its original shape fairly
8:06quickly a beanbag you'd hit it and it
8:08would just stay in that shape so it
8:10doesn't have the elasticity right so for
8:13all those reasons carpet doesn't
8:15propagate energy well however stiff
8:19objects do games make sense sort of the
8:23same way that you could say which would
8:26you rather get hit in the face with I'm
8:28going to throw a softball which of
8:30course you know right now it's not very
8:31soft or a water balloon which would you
8:35rather get hit in the face with and
8:36don't say neither the reason why
8:39hopefully most of you would say a water
8:41balloon because when it hits your face
8:42it just kind of deforms right it's it
8:46deforms it's not very stiff but the
8:49softball doesn't really
8:50shake very much it's gonna hit your face
8:53and it's gonna hurt neither one of them
8:55really change in terms wait I mean you
8:58might even say this one's heavier
9:00indicating this would hurt more but it
9:03doesn't because it's elastic and it's
9:06not a it's actually very compressible
9:08whereas this is non compressible which
9:11is the opposite a compressibility is the
9:14opposite of stiffness so stiff objects
9:17propagate well so inside the body when
9:21we come across stiff objects energy
9:24moves through it fairly well today good
9:31all right so that's the most important
9:34one whatever happens to stiffness inside
9:36the human body that's going to determine
9:39whether or not it propagates energy well
9:41the second most important one which was
9:44the one that was listed second previous
9:49page yes density benzene remember is
9:55mass per unit volume how heavy an object
9:58is does it make sense that the heavier
10:02the object is the harder it is to move
10:05that makes sense good so another way to
10:12look at it is say I'm chasing you around
10:14and I'm going to hit you with the steel
10:16baseball bat I'll give you two objects
10:18to hide behind one is a piece of paper
10:20one is a refrigerator hopefully you
10:24would choose the refrigerator because
10:26refrigerator is heavy it's not going to
10:30move much no matter how hard I swing
10:32that baseball bat I'm not going to move
10:34that refrigerator enough to really do
10:37much more than vibrate that refrigerator
10:39and slightly vibrate your body if I if
10:42there's any connection there over the
10:44piece of paper can move easily so non
10:47dense objects actually propagate
10:49extremely well so if we actually have
10:53high dent or low dense objects that are
10:57stiff is going to propagate it gate
11:00energy very well so what in the body
11:03we is not very dense and very stiff if
11:10any of you ever held a bone in your hand
11:12it's not very heavy is it and that's non
11:17dense remember mass weight per unit
11:19volume so bones are actually non dense
11:23objects that are very stiff this is why
11:26bone has a velocity of 4080 meters per
11:29second and soft tissue is 1540 meters
11:32per second
11:33hey so stiff non dense objects propagate
11:38energy the best everything else we've
11:42kind of discussed compressibility is
11:43simply the opposite of stiffness so if
11:47something has high compressibility such
11:49as a water balloon or something that's
11:51very deformable it doesn't propagate
11:54energy very well so if you have a highly
11:59compressible object it actually
12:01decreases your acoustic velocity and
12:03then lastly elasticity which is here
12:08again the ability to return to the
12:11original shape quickly so if you had a
12:14bunch of water balloons lined up in a
12:16row and a bunch of tennis balls lined up
12:18in a row and you hit one end which one
12:21would propagate that energy to the end
12:23better tennis balls or a bunch of water
12:26balloons and this balls because they
12:29would bounce back quicker right so if
12:31the lasting increases propagation speed
12:34will increase slightly but please
12:37remember density and stiffness are the
12:39most important things and I think that's
12:41actually a test questions all right so
12:48coming down to determining velocity it
12:51depends on the set of equations here the
12:56first one velocity equals frequency
13:00times the wavelength is the original
13:05formula here and then you can of course
13:07manipulate the formula solve for
13:09wavelength and/or frequency so we need
13:13to spend some time talking about this
13:15or formula so let's try to calculate
13:23them using this formula will calculate
13:29velocity in meters per second if the
13:34frequency is 2 megahertz and the
13:40wavelength is 0.01 millimeters so let's
13:45plug in the values remember to take
13:47frequency out all the way to 1 over
13:49seconds and then you can from there you
13:53should be able your units should come
13:54out okay so let's try that one on our
13:57own and see how we how we do simply
13:59plugging it in frequency then equals 2
14:03million 1 over seconds multiplied by
14:080.01 millimeters
14:10are there any metrics that we have to
14:13work out before multiplying this no
14:19there's not because there's no counter
14:23measurement for distance to 4
14:25millimeters
14:25and 1 over seconds there are no time
14:29limits and the other numbers so we can
14:31simply multiply this out so I'm going to
14:34add 1/2 here which means they have to
14:36take 1/2 away from here leaving that
14:39with 2 0 0 0 0 1 over seconds multiplied
14:44by 1 millimeter so that it is 20,000
14:51millimeters per second now we just have
14:56to convert it into meters per second so
14:5920,000 millimetres should be smaller as
15:04a big meter by 3 decimal places so
15:06moving back 1 2 3 we should end up with
15:0920 meters per second how'd you do now
15:16good where did we break down step 1 the
15:21formula yep really you chose the wrong
15:24formula
15:29where did you get where did you get a
15:31two million from remember raise that or
15:33we started this practice that remember
15:35to take the frequency out to one over
15:36seconds so two megahertz is two million
15:40one over seconds whenever dealing with
15:43frequency and you're doing some division
15:46or multiplication always take it out to
15:47one over seconds that way your units
15:49will come out perks and it'll be easier
15:53to do your math otherwise you're left
15:55with some ugly numbers and other ugly
15:57metrics to deal with you said always
15:59taking my game Hertz over whatever
16:01seconds always take all forms of
16:03frequencies up to one over seconds to
16:05Hertz
16:05okay all right so what I'm hearing is we
16:10need to do another one Kari says yes so
16:12we're gonna do another one I am going to
16:15do let's do the same thing this time
16:33we'll to a five megahertz transducer and
16:38this time we'll say that the wavelength
16:40is 0.02 milliseconds yeah waiting sorry
16:58not milliseconds Oh millimeters there
17:01you alright it's good that one shot I
17:06was just finding out where we're at but
17:08it sounds like a lot of you're pretty
17:10calm please do one more okay but let's
17:13let's see where this one where we ended
17:15up with again we're solving for velocity
17:17that's frequency and again we take it
17:19out to all the way to it's one over
17:21seconds five million one over seconds
17:24multiplied by 0.02 millimeters right
17:28there's really no metrics we need to do
17:30we can go ahead and multiply these
17:31together so one two three goes away here
17:35which means one two three goes away here
17:37so now I have five thousand
17:40one over seconds multiplied by two
17:44millimeters 5000 multiplied by two is
17:47ten thousand and that's millimeters on
17:52top seconds on the bottom we have a
17:56velocity here now we wanted it in meters
18:00so ten thousand tiny little millimeters
18:05converting it into meters which is much
18:07larger will make it one to three decimal
18:10places smaller the answer is 10 meters
18:13per second most of you gave me that
18:15answer is correct I know exactly what I
18:18did I accidentally put one times five
18:21thousand recording huh okay all right
18:42you can yell at me I'm just a hey
18:45practice right good point all right one
18:52more are we pretty good with this okay
18:55I'm saying velocity question there's
18:58different numbers okay that if you're
19:01okay I'm gonna make it slightly more
19:02complicated okay okay go back C equals
19:09frequency times wavelength see this time
19:12we're in goes centimeters per milli
19:14second question and then our frequency
19:19I'll make this easy we'll just say one
19:22megahertz and our wavelength will say
19:36let's see what happens here I'll say one
19:40micrometer
19:48so let's set this one up velocity again
19:52equals frequency which is 1 million over
19:57seconds multiplied by 1 micrometer all
20:02right again
20:03there are not really decimal places we
20:05have to try to get straight so it
20:08literally is 1 million multiplied by one
20:12the units will be micrometer is over
20:15second so 1 million micrometer per
20:21second all right so we need to convert
20:26it into centimeters per milli second so
20:30converting 1 million micrometer Xin to
20:33centimeters what is that conversion
20:41remember micro it's times 10 to the
20:43negative 6 centimeters times 10 to
20:45negative 2 so how many decimal places
20:47that we move in for and this is number
20:50gonna be figure is a centimeter or
20:52smaller as a centimeter it's smaller by
20:554 decimal places so 1 2 3 4 those are
20:59all gone so we're left with 100
21:02centimeters per second now we need to
21:06convert it into centimeters per milli
21:07second to item more or less time to
21:09travel as a milli second lattice
21:18milliseconds are less than seconds by
21:20how many decimal places 3 yep so
21:25starting here we go 1 2 3 decimal places
21:28left point one centimeters per milli
21:31second who got that right look at all
21:34the hands go up here Jamie you wouldn't
21:37believe it the whole class got that
21:39right actually nobody raised the hand so
21:44it looks like we have some more work to
21:46do so let's talk through about why that
21:48one was so much more difficult than the
21:50others that you were feeling more
21:51confident about there's nothing really
21:54changed
21:57I didn't know what to bring down after
22:01we times the 1 million won over seconds
22:08to bring them what do you mean I didn't
22:11know to bring the microseconds of the
22:12second step oh well like all the other
22:16ones before remember we didn't do any
22:17conversions before we just moved some
22:20decimal places around so the math would
22:21be a little bit easier and since the
22:23math already is easy 1 million times 1
22:26we just brought the same units down that
22:29is distance over time that makes sense
22:32ok all right so I think we need to do at
22:36least one more
22:38so again velocity will go millimeters
22:44per Mille second let's say our
22:49wavelength is 0.02 millimeters and our
23:02frequency is 10 megahertz let's try that
23:07one
23:11alright so looking at this one again
23:17velocity equals frequency which is 10
23:20million 1 over seconds multiplied by
23:250.02 millimeters okay so let's make the
23:30math a little easier we're going to go
23:31and head and take away 2 here or just re
23:34add 2 there and then take away 2 here so
23:37that will leave one two three four five
23:41zeros so one two three four five zeros
23:45so that's a hundred thousand one over
23:48seconds multiplied by two millimeters
23:51which ends up being two hundred thousand
23:56millimeters per second and we want to
24:00convert it to millimeters per
24:03millisecond okay so just looking at the
24:07numerator we don't have to burn anything
24:08mmm
24:09are millimeters looking at the bottom
24:11seconds two milliseconds
24:13I have less time to travel in a
24:17millisecond and that's going to be three
24:19decimal places less so this comes back
24:21to one to three decimal places our
24:24answer is 200 millimeters per
24:27millisecond you all are correct
24:33okay so that's just solving for velocity
24:37which we all seem I hope well let me
24:39just ask does everybody feel a little
24:41bit better about velocity now one person
24:45shaking their head Jamie
24:47Kira do you feel better about this down
24:50here I can't doubt that yes was already
24:52answering like kinda okay well how about
24:55how about we do this how about we move
24:59on we're use the same formula just
25:02manipulating manipulating in different
25:04ways and solving for different variables
25:05and maybe it would become more
25:07comfortable with it so I mean sense okay
25:10so again the original formula is
25:13velocity equals frequency times
25:14wavelength this time I want to solve for
25:17frequency and it will be manipulated
25:20this way so velocity will be divided by
25:23wavelength so let's take a velocity of
25:291,000 meters per second and a wavelength
25:33of 0.01 millimeters and let's find a
25:40frequency and let's just say Hertz
25:43that's what we're looking for okay
25:46let's give that a shot Jessica done work
25:52in there okay
25:53Kiera Jamie how you doing have an answer
25:57whether it's right or wrong okay Amy
26:12you must be on snack break or something
26:15okay so frequent whoops
26:21frequency equals velocity 1,000 meters
26:26per second divided by 0.01 millimeters
26:29okay so are there conversions that you
26:33need to make before doing this and we
26:37divide millimeters into meters nope
26:41so just out of curiosity how many you
26:44converted the velocity into millimeters
26:47per second now the sole because you guys
26:51are definitely afraid of the velocity
26:53okay so everybody converted millimeters
26:57centimeters making it a worse decimal
27:00problem okay so then this would be
27:03meters one two three okay so now you
27:08have one thousand meters per second
27:11divided by 0.001 meter right right
27:20everybody got that conversion correct
27:22yeah no okay all right so now we're
27:30gonna have to add one two - three - four
27:33five their cheese may have to add one
27:36one two three four five oh my gosh ran
27:41out of space one two three four five
27:45okay so then we end up with the 1,000
27:50then we added one two three four five
27:53decimal places and that was still in
27:57meters per second divided by 1 meter
28:01meters will cancel out we're left with 1
28:04over seconds which is good because we're
28:06looking for a frequency and we have
28:09let's see 3 zeroes there 3 zeroes there
28:12so that's up by being 100 million won
28:18over seconds or Birds right how many
28:24ended up with 100 million
28:27nobody anybody gear up Jamie anybody
28:32hung up with 100 million Hey
28:38all right well you're not alone all
28:40right so another one so again solve for
28:46frequency and this time with one
28:50megahertz if the velocity is we'll go
28:552,000 meters per second and the
29:00wavelength will say is 0.01
29:10I don't 1 millimeters hey let's get that
29:17one shot kill any more confident with
29:25this one still working game you still
29:34with us all right
29:40okay go say how do you feel are you
29:42feeling any better
29:43what's out yeah all right so frequency
29:53again equals velocity divided by
29:55wavelength we have 2000 meters per
29:59second and altered divided by oh I
30:01almost got kicked off their millimeters
30:05now did you guys go with the converting
30:08millimeters again 2 meters or did you
30:11try converting the velocity it's okay
30:16just tell me which way you want me to
30:17work millimeters centimeters okay so
30:23again that's gonna be one to three
30:25decimal places back we end up with 2,000
30:29meters per second divided by point one
30:32two three four zeros meters right
30:38so leaders will cancel out we left with
30:41one over seconds so you need to add one
30:44two three four five decimal places here
30:47since we need to add one two three four
30:50five decimal places here gonna so we end
30:56up with two zero zero zero zero zero
30:59zero one zero zero alright so there's
31:02three there's three two hundred million
31:10Earth's and then converted into
31:13megahertz they separate each other by
31:16six decimal places megahertz is much
31:18bigger than a Hertz so it's gonna be
31:20smaller one two three four five six
31:24answer is 200 megahertz
31:29you guys good you're on the right track
31:39okay did you all the rest of you get 200
31:42megahertz yes Emily alright let's move
31:49on to the last way to convert this
31:52particular problem which is solving for
31:54wavelength which is velocity over
31:56frequency so let's take philosophy of
32:011,000 meters per second and a frequency
32:05of 2 mega Hertz get that one a shot
32:11Jamie also came out and Hertz on that
32:13last one we just convert it to mega
32:18Hertz after that that's fine the meters
32:27per second with it
32:29let's write me well if there are no
32:33meters in the denominator you sided
32:36touch the meters you make it hard on
32:40yourself Jessica well
32:48it's okay to tell me just where you're
32:50at you can say I I didn't even want to
32:54be here okay Jamie hero where yeah you
33:02come up with an answer are you
33:05comfortable with it or you like
33:09everybody else you're not really sure
33:10what you got or why you have it you have
33:12an answer
33:13are you confident with it but I'm sure
33:16okay all right
33:17all right so let's take a look at this
33:19one so this is different this is first
33:21time trying this so it makes sense that
33:23you would be unsure about what to do
33:25with it
33:25so the last thing again we just set it
33:28up on top 1,000 meters per second
33:30divided by 2 million remember because we
33:33always take frequencies out to 1 over
33:35seconds do we have to do anything
33:38are there any metrics that we have to
33:40convert prior to doing your math here no
33:42there's absolutely nothing we need to do
33:45all right so the seconds eventually will
33:48cancel out we're going to end up with
33:50meters as our answer which is good
33:51because we were looking for a wavelength
33:53and wavelength the symmetric and
33:55distance a meter is a distance the issue
33:59is here is we just have to do math so we
34:02have 2 million divided in I gotta draw
34:09this backwards and will kick me out
34:10dividing into 1,000 but 2 million does
34:16not go into 1,000 so we put our decimal
34:19here is not going to ten thousand a
34:21hundred thousand just going to 1 million
34:25but will go into 10 million preserving
34:28our decimal places for each 0 we just
34:29added to get up to ten million two
34:31million goes into 10 million how many
34:33times not done we already said that our
34:40units were in meters up here right whoa
34:44sorry so our answer is 0.12 three zeros
34:52five meters did anybody get that answer
34:57come on two
34:59- and you said you weren't sure yeah
35:02Emily yeah no you didn't get anywhere
35:08near that how come oh why did you you
35:16said you didn't get near that either
35:17why sending it up correctly the key all
35:25right so try not yes no you want to move
35:31on to other things
35:37wait okay what am I waiting for
35:41I'm so excited turn on a webcam in the
35:49magitek oh yeah I was definitely gonna
35:55raise that singing and you gotta go get
36:02it on the recording yeah just wait in
36:14the future
36:15just tell me I guess - look I don't know
36:18how else to not erase it other than you
36:22saying wait so just let me know and I'll
36:24I'll hold it until everything's good
36:26alright so we were solving for
36:30wavelength right so this time let's do
36:33wavelength and I want it in centimeters
36:36if the velocity is let's do something
36:39fun like 15 40 meters per second and
36:42let's do a frequency of let's say 1
36:45megahertz this is like a real situation
36:48what are what is our wavelength using a
36:511 megahertz transducer and soft-tissue
36:56did you feel very confident about it
36:58I feel so so bad ok so near 71
37:06Anna still rating are you good yeah yeah
37:12do you have an answer
37:13yeah confident Jessica but you have
37:20something that's good all right
37:25Kira Jamie you have something you have
37:29an answer okay
37:30confidence level Oh so Jamie confidence
37:38level do you have something what's a kid
37:53ninh all right it's uh wavelength equals
38:00velocity fifteen forty meters per second
38:03divided by 1 million one over seconds is
38:08there anything we need to do prior to
38:10doing your math yeah we can just divide
38:14this one up I'm gonna just go take it
38:17back to one so we go one two three four
38:20five six decimal places which means I
38:24have to do the same to the top one two
38:26three six so I end up with point oh oh
38:32one five four meters per second divided
38:36by one one over seconds and again the
38:40seconds cancel out we're left with
38:43meters and point mole 1 5 4 divided by 1
38:47is 0.001 5 4 units are meters are we
38:53done no because we said we wanted their
38:56answers in centimeters so centimeters
38:59are smaller than a meter which means
39:01this is going to become a bigger number
39:03by two decimal places
39:05one two decimal places we end up with
39:100.15 for son of years that is our answer
39:15how did you guys do I actually did
39:18pretty good good but I did it different
39:22what do you that's okay so I had it
39:26set up as the 1 million and then divided
39:29by the 1540 and then I just kept having
39:31the zeros but I added one more 0 ok you
39:36got lucky and then I looked at it myself
39:42yep make sure you plug in the numbers at
39:45the right places carry got close well
39:49hopefully close enough that you could
39:50have chosen a B C or D right that's all
39:53we're working on all right how are you
39:58feeling about solving for wavelength
40:00pretty good hey let's take it one step
40:03further and let's let's see let's solve
40:11for velocity in meters per second if the
40:21wavelength is 0.01 centimeters and the
40:28period is less you let see point oh one
40:42micro seconds enjoy
40:55yes no how no maybe
41:01yeah here says yes Morgan says no
41:05Jessica
41:09Brooks you're definitely saying you
41:11don't know anything I wanted to know
41:15your answer just one I do have did you
41:18not very confident okay have something
41:22okay we gave up somewhere again okay all
41:25right all right so the issue with this
41:29one is that we don't have everything we
41:31need to actually just plug in the
41:33numbers and come up with an answer like
41:35we did before but we do have enough
41:37we can calculate this we understand that
41:40period has a relationship with frequency
41:43which is what we need to actually
41:44calculate the velocity so last week we
41:48talked about doing reciprocals to get
41:52frequency in period remember that right
41:58so 1 divided by 0.01 and this would be
42:02mega and this would be heard so 1 2 1 2
42:07so the reciprocal of period of 0.01
42:13microseconds would give us the frequency
42:15of 100 mega Hertz correct how many got
42:22that far
42:23wait is that the problem
42:28just everybody understand how I got 100
42:30mega Hertz frequency from 0.01 micro
42:34second period yes okay
42:41many people shaking their heads and
42:42saying yes that was last week
42:45doing reciprocals all right so now I'm
42:47moving forward if you knew that the
42:49frequency was 100 mega Hertz could you
42:50then solve it from this point forward
42:52okay let's give it a shot but let's just
42:54say frequency is 100 mega Hertz wave
42:58length is 0.01 centimeters what is the
43:01velocity in meters per second let's take
43:03it from there I'm pretty confident
43:21Brook just look like they're still
43:24working Morgan a little bit yeah you
43:28double checking okay I'm just gonna set
43:36this up and try to create more space we
43:40don't confuse ourselves
43:42so velocity would be our frequency
43:53multiplied by 0.01 centimeters so that
43:57would be one hundred million one over
44:02seconds multiplied by 0.01 centimeters
44:07right here if I get that far
44:10so is there any metrics conversions that
44:15have to take place in order for us to
44:16get the velocity from these two values
44:19metrics conversions no we can come up
44:23with centimeters per second worried
44:25about the conversion later so
44:27mathematically I'm just gonna add two
44:30decimal places here and turn it into one
44:32centimeter which means I have to take
44:33two decimal places here take those zeros
44:36away so then we end up with that 100 and
44:41then one two three zeros and then one
44:43more zero leftover multiplied by one
44:47centimeter this is of course still
44:50one-upper seconds so what is this that's
44:53three decimal that's 1 million multiply
44:565 1 so we end up with 1 million
45:02centimeters per second now we wanted our
45:06answer in meters per second it's nice to
45:10see that the denominators are already in
45:12second so we simply have to make a
45:13conversion of 1 million centimeters into
45:16a meter is that gonna be a bigger or
45:19smaller number once it's converted into
45:20a meter smaller by how many decimal
45:24places separate centimeters for meters
45:26to so we take back two decimal places
45:30and we're left with one zero zero zero
45:33that last zero there and that's gonna be
45:37meters per second so 10,000 meters per
45:41second it's our answer how many of you
45:45got back 1 2 3
45:49Jessica no Brooke I got it we did
45:53together oh I was not I was starting on
45:58to the my noodles I mean I was on her a
46:04path okay
46:06okay all right so you were almost there
46:08you just here says yes she's got that
46:12okay
46:13so let's try one more of these where we
46:16bring in period and then calculating the
46:19frequency all together now it's like hey
46:20there's a question on the next test just
46:23like so let's look at again calculating
46:30the velocity no let's switch it up let's
46:35calculate the wavelength in millimeters
46:39if the velocity is 1,000 let's make it
46:46confusing centimeters per milli second
46:51and the period is we'll say point 2
47:08microseconds there we go okay so we have
47:12all the tools we need take the steps to
47:15find the correct variables that you need
47:19so you can plug it into the formula use
47:21the correct formula manipulate it
47:23correctly but your numbers then do your
47:27metrics conversions do your math and
47:29then conversions back to milliliters you
47:37have anything
47:43you're waiting on this one also why why
47:47why is this what's with this just like
47:48the last one right no okay well first of
47:54all let's find the variables that we
47:56need again we need to find frequency and
47:58we have the period so setting up the
48:04reciprocal of 0.2 micro seconds why
48:10that's there you know well that went
48:17much long that small okay so 1 divided
48:21by 0.2 micros we know it's gonna be mega
48:24and there's a whole of seconds is going
48:28to be Hertz so just adding a decimal
48:33place here we're gonna add here so 2
48:37divided into 10 is going to be 5 and
48:41that's gonna be mega Hertz so the
48:44frequency is 5 megahertz from a period
48:49that is point 2 microseconds correct
48:54glad you all wholeheartedly agree that
48:57I'm right on that one okay good so then
49:00setting it up wavelength equals velocity
49:03divided by frequency velocity in this
49:06case will be 1,000 centimeters per
49:09millisecond that's that's not this again
49:14millisecond and the frequency is
49:195,000,000 won over seconds can we divide
49:23those out no because we have centimeters
49:28per milli second on top and 1 over
49:31seconds on the bottom so they don't
49:33match so remember we always want to make
49:36it 1 over seconds so looking at the
49:40velocity in top centimeters per milli
49:42second should be changed to centimeters
49:46per second so let's make that conversion
49:491,000 centimeters two centimeters
49:51there's no conversion
49:52necessary looking at the bottom of going
49:54from milliseconds to seconds to a more
49:56or less time to travel more by how many
50:01decimal places more how many does the
50:05place apart be one two three so now we
50:10have 1 million centimeters per second
50:16divided by five million one over seconds
50:23so now things kind of look a little bit
50:26easier now the seconds cancel out now
50:29we're going to end up with centimeters
50:30as our answer and now we just have to
50:32divide 1 million by five million but
50:35we're gonna make that a whole lot easier
50:37because we're gonna take out six zeros
50:38on top and on bottom and now we just
50:40have five divided into one so 5 goes
50:43into one zero times but it goes into 10
50:49twice or 0.2 so our answer is 0.2
50:54centimeters are we done
50:58no because we said we wanted our answers
51:01in millimeters so converting centimeters
51:04into millimeters gonna be a bigger
51:08number by one decimal place two
51:11millimeters is our answer even get that
51:17right you could new spot that is you're
51:23not alone so where did we go wrong what
51:30division down here whenever I divided
51:42two into ten I didn't put the two mean
51:48five into ten yeah okay everybody got
51:54the velocity conversion correct yeah
51:57it's where I anticipated a lot of this
51:59goes there's there's this common fear of
52:02velocities I don't know what it is
52:05but like nobody wants to touch this and
52:10clearly it doesn't match this though
52:17understanding that all you have to do is
52:19know what your converting it to and if
52:24you are comfortable with those
52:27conversions then it would make this a
52:31whole lot easier but I've been kind of
52:33saying that since day one it's gonna
52:35take some time and some effort to become
52:38really comfortable with those times so
52:40for conversions all right so what do I
52:45do no all right let's see we've done
52:58wavelength we can't do any other one so
53:00let's go back to velocity let's make it
53:05meters per second let's do a wavelength
53:14of 0.01 millimeters in a period of 0.1
53:22microsecond
53:23let's try that so I'm assuming this
53:29point everyone has finished step one
53:32which is converting period into a
53:36frequency taking the reciprocal of one
53:40microsecond one divided by point one
53:47super cloak micro is mega Pacific log
53:51seconds is Hertz adding a decimal place
53:56here and adding one here makes that 10
53:58over 110 mega Hertz is our frequency I'm
54:10plugging it in velocity equals frequency
54:13times wavelength that will equal to ten
54:17million
54:19one over seconds multiplied by our
54:23wavelength which is fine alone
54:26millimeters right everybody's at that
54:30point Dappy it's okay I mean this was a
54:41lot of math today but it was in an
54:44effort to make you feel a little more
54:45comfortable with it so I just you know
54:47like literally the keep this repeat this
54:50repeat this every single day like three
54:52times sitting that's great because now
54:54you can go home and watch this again I'm
54:57gonna do it okay
54:58all right all right so let's finish this
55:03one out and see if you guys would have
55:07been on the right track so I'm up to ten
55:09million won over seconds multiplied by
55:110.01 millimeters again there's nothing
55:14really we need to do we can go ahead and
55:16multiply these two out I'm gonna add two
55:19decimal places here again turning this
55:20into one millimeter and then that means
55:23I got to take away one two decimal
55:25places here and I end up with that
55:28original 10 those three zeros and that
55:31one extra zero I have 100,000 my units
55:35are still one over seconds so I have a
55:37hundred thousand one over seconds
55:39multiplied by one millimeter or one
55:41hundred one hundred thousand millimeters
55:45per second we said we wanted our answers
55:49and meters per second the thing is we
55:51don't have to convert the denominator
55:53but the numerator millimeters into
55:56meters that's gonna change by three
55:58decimal places and it's gonna be three
56:01decimal places smaller it's a big meter
56:03so we're an end up with 100 meters per
56:06second as the final answer that looked
56:11like the direction you were heading okay
56:14all right here's what I'm gonna
56:16recommend I recommend that we because
56:18we've done so much math we do have a
56:22little bit more to cover probably about
56:2420 more minutes of material and then
56:27we're going to go to lab so why don't
56:30you take five minutes and up off around
56:31gets
56:32but move into your legs and then we'll
56:34come back and we'll finish up chapter 2
56:36okay so five minutes
56:41the last part of chapter two deals with
56:47I want to stay energy generally speaking
56:51and energy can be divided into power and
56:54intensity and the units of which we do
56:57to describe those measurements of power
57:02so power and we think about output power
57:08of your machine which is the ability to
57:12do work how much energy does it have to
57:15do work so your transducer for example
57:19has the power to push a pressure wave
57:23inside the human body now what happens
57:26to that energy that overall power as it
57:28propagates or moves through the
57:30patient's body it changes because the
57:34parameters of the beam change as it
57:36moves through the body so one particular
57:40component of power or a more specific
57:44measurement of its power is intensity so
57:47let's make let's let's describe the
57:49difference between power and intensity
57:51so everybody's familiar with people
57:57taking a magnifying glass and burning a
57:59hole in paper by using the Sun right you
58:02familiar with this process okay so if
58:05it's a bright sunny day and you have a
58:07piece of paper and a strong-enough
58:08magnifying glass and if you hold it long
58:10enough it will build up enough heat
58:12content that Sun concentration over a
58:15small spot will build up enough heat on
58:17the paper that will actually start to
58:19burn smoke and turn into flames right so
58:22the concept of intensity is very much
58:24like this so think of Sun as the overall
58:27power if we walk out side pieces of
58:31paper just don't flail up in flames
58:33right it takes a concentrated portion of
58:37that overall power over a small
58:40cross-sectional area
58:42concentrated in one particular area
58:45to create that kind of heat that makes
58:46sense so intensity is that power
58:50concentrated over a much smaller area
58:53and this is what happens as the
58:55ultrasound beam begins to travel is it
58:58turns into a focus we focus the beam
59:01like we focus a picture but when we
59:04focus the beam what we're really doing
59:05is taking all that energy and putting it
59:07in a smaller space so that overall power
59:11pressure area and then we concentrate it
59:13into a smaller space this creates an
59:18intensity that we have to monitor to
59:21make sure that we don't have too much of
59:23it or we can cause irreversible
59:25biological damage so power here let me
59:32get my hour whoops here it's a total
59:41energy over the entire area so that
59:47transducer as it's exposing your patient
59:50power is simply all of that energy over
59:53the entire area you're scanning it's
59:57units of measurement is watts now this
1:00:04is different from intensity because
1:00:09intensity it's not on here intensity is
1:00:15the amount of that energy within a
1:00:21specific area per second and it's units
1:00:28are watts per centimeters squared it's
1:00:37that power over a specific area so it's
1:00:43intensity that we're most worried about
1:00:45it is we don't want to burn the paper or
1:00:48we don't want to cause irreversible
1:00:50biological damage to our patient if the
1:00:53intensity is too high and just to give
1:00:56you some idea of the types of things
1:00:57that
1:00:58high-intensity ultrasound can do that
1:01:04the process known as lithotripsy you
1:01:06ever heard of this shatters stones
1:01:09inside of your body it also is used
1:01:12ultrasonic energies also used to destroy
1:01:15plaque on your teeth
1:01:16literally shatters it ultrasonic energy
1:01:21has the capability of heating up tissues
1:01:24to the point where it can synthesize DNA
1:01:27in your body it's extremely powerful
1:01:31energy so it's not something you mess
1:01:36with at the wrong level so it's very
1:01:38important that we monitor the levels
1:01:39that we're looking at or that we're
1:01:42using on our patients body to make sure
1:01:43that we don't shatter bone inside of our
1:01:46patients or synthesize their DNA or do
1:01:49anything of that nature so it has the
1:01:51potential to do some great damage it's
1:01:54generally noticed that that we say that
1:01:57ultrasound energy at diagnostic levels
1:01:59which is what we do is generally safe
1:02:02and that is a true statement but it
1:02:04doesn't mean we shouldn't be aware of
1:02:06what we're doing because the potential
1:02:09for danger is there okay so how do we
1:02:14actually measure them the amount of
1:02:17intensity or power we push into our
1:02:20patients and that's where this last part
1:02:22comes in there are some formulas
1:02:24intensity and amplitude which is
1:02:27strength amplitude is this we talked
1:02:30about amplitude earlier or last week we
1:02:32talked about the strength of pushing and
1:02:34pressure inside the patient's body and
1:02:38intensity is just a new way to measure
1:02:40this off of the total power we're giving
1:02:44to our patients there is a relationship
1:02:46between power and intensity amplitude if
1:02:49you increase your power you will
1:02:50increase your amplitude and you will
1:02:52increase your intensity these are all
1:02:54true statements so there is a
1:02:56relationship and you'll notice that
1:02:58looking at the two formulas that
1:02:59calculate intensity in amplitude they're
1:03:02very similar one is twice that of the
1:03:05other you notice one starts out with a
1:03:06ten and one starts out with the twenty
1:03:08other than that it is comparing
1:03:11- values what is the new value compared
1:03:16to the original what is the new value
1:03:18compared to the original and then we're
1:03:21multiplying the log of base 10 of that
1:03:23either multiplied by 10 or by 20 so the
1:03:27amplitude form of it is simply twice
1:03:29that of the intensity form of it in
1:03:32terms of decibels which is the way we
1:03:36measure how much power or intensity or
1:03:40in amplitude we are giving to the
1:03:43patient now you might say well why would
1:03:45you have an amplitude and why would you
1:03:47have an intensity and why would you have
1:03:51a logarithmic scale that describes its
1:03:53decibels either way it turns out it's
1:03:56because what we're measuring so to put
1:04:00it very simply the intensity form let me
1:04:06pull up the that didn't work okay let me
1:04:25try this again give me just a second
1:04:44started for the delay it was loaded but
1:04:47some reason it's not trying it's not
1:04:52showing again oh maybe it was at the top
1:04:58before okay alright so this whole thing
1:05:02you just need to memorize but there's
1:05:06some pattern to it so once you memorize
1:05:07a couple things everything else falls
1:05:10into place so first of all let's look at
1:05:14the differences so one we have power
1:05:19clips where we have the power and we
1:05:25have amplitude form if you simply look
1:05:27at the columns you'll notice that if we
1:05:31hate take 20 decibels in the power form
1:05:3440 decibels are simply doubled up it's
1:05:37true throughout the entire grid and the
1:05:40school's 20 decibels 9 decimals 18
1:05:42decibels so amplitude as always as the
1:05:45formula has indicated twice that up the
1:05:47intensity form a so there's a process to
1:05:52this and I'm trying to explain the
1:05:54difference between power and intensity
1:05:56versus amplitude and the big difference
1:05:59is outlined below here's why why this
1:06:06one and still going up black here
1:06:11power is used to describe power of
1:06:16course intensity and anything measured
1:06:18in watts or watts per centimeter squared
1:06:21those are the units to describe power
1:06:22and intensity amplitude form is anything
1:06:26else so if I were to say we've increased
1:06:31the voltage of our transducer 100 times
1:06:36its original value you would know we're
1:06:37talking about an amplitude change
1:06:40because voltage is specific to amplitude
1:06:43voltage has nothing to do with power and
1:06:45intensity if we increase the temperature
1:06:49of the patient's body we could actually
1:06:52record that in decibels because that's
1:06:56an amp
1:06:57to form temperature is one of those
1:06:59things inside amplitude it is not
1:07:02something that is recorded in power or
1:07:04intensity so let's talk about the
1:07:08patterns and how we get to understanding
1:07:11how this works so all of our machines
1:07:15start at a power value of zero decibels
1:07:20this doesn't mean it has no power it
1:07:23just means it's the power level that it
1:07:24starts up you start up the Machine you
1:07:27set the transducer down and it starts
1:07:29creating ultrasound images the power
1:07:31it's emitting into your patient is
1:07:34recorded at zero decibels that's just
1:07:36its default power level and every
1:07:39machine has a different power default
1:07:43mechanism so just because zero decibels
1:07:46on this machine will not equal zero
1:07:48vegetables on the next machine they're
1:07:50not equivalent all they're really doing
1:07:53is saying this is my starting point
1:07:55alright so from there we then need to
1:07:59make decisions about whether we need to
1:08:03increase our power or decrease our power
1:08:06based on the patient that's in front of
1:08:09us so let's say for example I'm scanning
1:08:12and understanding that the power level
1:08:16we start out with is based on
1:08:19average-sized people and let's say the
1:08:24next patient that comes in is 600 pounds
1:08:26now what we call average so we're going
1:08:31to have to increase our power right
1:08:33we're going to need more strength to
1:08:35push that pressure wave into this
1:08:38patient so we start by increasing that
1:08:41power and just like a volume knob on
1:08:43your stereo at home you move up a click
1:08:47the first click you're going to hit is a
1:08:51positive 3 decibels it's not on 1 or 2
1:08:55or 3 it's positive 3 decibels that's the
1:08:58smallest increment you can go by
1:09:01positive 3 decibels is this next one
1:09:05here any power a positive 3 decibels
1:09:10or lanes to 200% its original value or
1:09:13two times its original output power it
1:09:18turns out every time we move it up one
1:09:20more click it goes up another 3 decibels
1:09:23so the next one two clicks up is just
1:09:26three decibels more and it turns out it
1:09:29doubles it again
1:09:30so every three decibels you double your
1:09:33output power three decibels is twice as
1:09:36much six decibels is four times as much
1:09:40nine decibels is eight times you just
1:09:44click it up three decibels until you get
1:09:47to 10 so three twice as much six four
1:09:53times as much
1:09:53nine eight times as much 10 10 times as
1:09:59much that okay so far it turns out the
1:10:04opposite is true let's say we don't have
1:10:06a 600 compeition instead I have a child
1:10:09let's call let's say it's a
1:10:10five-year-old kid tiny skinny little kid
1:10:13all right so we don't need the original
1:10:16output power been standing on my
1:10:18patience with the first click I go is I
1:10:20start okay I need to dial Islamic for my
1:10:22first like is -3 decimals and instead of
1:10:25being twice as much with a positive 3 to
1:10:293 decimals and negative 3 decimals is
1:10:31half or 50% of its original value so you
1:10:37can imagine the next three decibels is
1:10:39half that again or 25% the next 3
1:10:44decimals is half that again or 12 and a
1:10:47half percent and then when you get to 10
1:10:49it's 10% of its original value though
1:10:53all those make sense to you so if a the
1:10:58large patient comes in and I increase my
1:11:01decimals by 6 decibels how many times
1:11:06have I increased my output power
1:11:08successful x' four times the original
1:11:15value right three would be twice six
1:11:19would be four times right if I increase
1:11:21my output power because Mike
1:11:23bigger ten times original value what
1:11:26would be the corresponding decimal but
1:11:30ten right up here at ten decibels it
1:11:35would be ten times the original value so
1:11:38remember this is the your dial this is
1:11:40your volume knob so instead of going by
1:11:42ones you're gonna go three six nine ten
1:11:45or minus three minus six minus 10 or
1:11:48minus nine minus 10 right okay so all of
1:11:54these are in power form and like we said
1:11:57earlier amplitude is simply twice that
1:12:00and it would be recorded in different
1:12:02types of things so earlier all I talked
1:12:04about is power so let's say in this case
1:12:08in order for me to get the power level I
1:12:11need I've increased my voltage twice its
1:12:18original value so starting here going up
1:12:23two times which is here two times the
1:12:26original value would not correspond to
1:12:29three because we're not in the power
1:12:30form it would correspond to six because
1:12:34we're in the amplitude form because I
1:12:35said voltage makes sense where you say
1:12:39that yep so go back again I'm going to
1:12:43increase my voltage two times so two
1:12:47times would be 200% or two times right
1:12:52and because I said voltage I'm in the
1:12:54amplitude form that would be six
1:12:57decibels
1:12:58it would not be three because I'm not
1:13:00talking about power or intensity watts
1:13:03or watts per centimeter squared I'm
1:13:05talking about voltage okay so it's same
1:13:09thing what if I needed to increase my
1:13:13voltage to my transducer ten times
1:13:15original value what would be the
1:13:17corresponding decimal 20 that's right so
1:13:2110 is here 10 times it would be 20
1:13:24decibels that's not too bad is it okay
1:13:27let's say hold out a small kid got to
1:13:29cut my voltage back in half what is my
1:13:31corresponding decibel
1:13:37negative six right so half would be
1:13:40minus three in power before we talk
1:13:42about voltage so it would be minus six
1:13:44decibels not too bad right okay so now
1:13:48it turns out that these tiny little
1:13:51cliques of our dots if you actually saw
1:13:53it on the screen it actually just some
1:13:55think that big of a difference so the
1:13:56difference between three six nine not
1:13:58too big so turns out our dial has to be
1:14:00pretty big so this is why we have values
1:14:03above ten times its original value or
1:14:07smaller than one-tenth its original
1:14:09value we actually go up to a this should
1:14:12be an extra zero by the way we actually
1:14:14go up to like a thousand times the
1:14:16original value and one one thousandth of
1:14:18the original value so after ten decibels
1:14:21we simply go up by ten decibels after
1:14:23that making bigger leaps and bounds so
1:14:27at 10 positive 10 does it start when we
1:14:30get this stuff off at a 10 times
1:14:33original value were at 10 decibels in
1:14:35the power form 20 decibels is again 10
1:14:41times more than that or 100 times 30
1:14:43decibels is 10 times more than that or a
1:14:45thousand times and the opposite is true
1:14:48at 1/10 the original value is negative
1:14:5110 1/100 of the original value is
1:14:54negative 20 one one thousandth of the
1:14:57original value is negative 30 and on and
1:15:00so forth so you might say what in the
1:15:04world would we use this for I mean
1:15:06seriously what would we use this for so
1:15:08let's talk about there's a really good
1:15:10exercise inside your textbook can I see
1:15:13your textbook so I'm just so I can I'll
1:15:14give you the exact pages this looks
1:15:16extremely cumbersome when you first look
1:15:20at it and right now you're saying
1:15:22there's no way I'm going to know this
1:15:24after going to the exercised and me
1:15:27leaves book no one has ever missed a
1:15:30question on any of my tests regarding
1:15:31decimals and you would say gee do I have
1:15:35to memorize all this because there's a
1:15:37lot of patterns on here you would think
1:15:39you need to memorize everything but it
1:15:41really makes a whole lot of sense so I
1:15:44know that these this exercise is
1:15:51assigned in your syllabus but I just
1:15:58want to point it out because this will
1:15:59actually after you do these exercises
1:16:02it'll make a whole lot more sense just
1:16:04gotta get to the right page sorry almost
1:16:18there
1:16:18coming up on it there it is okay
1:16:21starting on page 37 exercise thirteen
1:16:27point seven so what I want to do is go
1:16:30over just a couple of these questions so
1:16:31you understand like what we're talking
1:16:33about and you'll see that they're not
1:16:35that bad
1:16:36so the first question on exercise
1:16:39thirteen point seven that says I have a
1:16:42niche initial power of 1000 watts - I'm
1:16:48reading it right I got my wrong I got my
1:16:50bifocals on I can't read anything in the
1:16:52dirt I think that says initial for me
1:16:56that's final first set PDF oh sorry
1:17:01so p.m. so final is actually a thousand
1:17:04Watts initial is 10 watts okay so it
1:17:08wants to know what is the change in
1:17:09decibel so according to this is you're
1:17:11starting out with 10 watts of power and
1:17:14you've increased to a thousand watts
1:17:15what is that change what do you multiply
1:17:18by 10 to get to a thousand five ten okay
1:17:28so 10 times 10 would be what a hundred
1:17:31it would be quite a thousand so what do
1:17:33you multiply 10 by to get to a thousand
1:17:37hundred right okay so what we have done
1:17:41is we've increased it 100 times and we
1:17:45said it was in the power form so looking
1:17:47at this chart powered form what is a
1:17:51hundred times the original value what is
1:17:53that corresponding decibel was that
1:17:58corresponding decimal
1:18:0120 decibels right there okay let's try
1:18:06this one input receiver is 1 millivolt
1:18:10output receiver signal is 100 millivolts
1:18:13so I started with 1 millivolt and I
1:18:16increased it to 100 millivolts what is
1:18:19my increase how many times 100
1:18:24so I've increased it a hundred times in
1:18:27voltage what is that corresponding
1:18:29decibel it is 40 that's right so again
1:18:36because it's asking about voltage were
1:18:39in this column and it said a hundred
1:18:42times or into 1 millivolt - 100
1:18:44millivolts it's a hundred times of
1:18:45course onion decibel is 40 decibels
1:18:48right so and then there's some questions
1:18:51about dollars don't worry about that
1:18:53try this one a decrease in power by a
1:18:58factor of two is equivalent to how many
1:19:00decibels factor of two means divided by
1:19:072 or 1/2 so decreasing the power by 1/2
1:19:13what is the corresponding decibel they
1:19:16want negatives reading them that's right
1:19:21so again 1/2 power form minus 3 what
1:19:27would be 1/2 or amplitude form 6 what
1:19:33would be 4 times the original value 4
1:19:35power form be positive 6 4 power put 4
1:19:43times the original value for amplitude
1:19:45form positive 12 right here's one number
1:19:5111 an increase in amplitude by a factor
1:19:53of a hundred is equivalent to what
1:19:55decibel 40 Emily you're right hundred
1:20:06times amplitude 40 we catching on to
1:20:08this ok all right so please go to your
1:20:11exercises thirteen point seven after you
1:20:13do that you'll find this
1:20:15actually much easier than it looks I
1:20:17know it looks intimidating now it's
1:20:18really not alright so let's talk about
1:20:22the process of attenuation because right
1:20:24now we're talking about sending power
1:20:26into our patient why would we need to
1:20:28son oh sorry
1:20:30why would we need to send more power
1:20:33into our patient it turns out that
1:20:36people attenuate sound attenuate means
1:20:40to slow down or to absorb or to lessen
1:20:44so here's how so looking at attenuation
1:20:57our patients typically up slow down our
1:21:01energy at 0.5 to one point zero decibels
1:21:06per centimeter it travels per megahertz
1:21:09and transducer we use you're saying what
1:21:13in the world is that mean we just talked
1:21:15about decimals right how much we have to
1:21:17increase decibels power intensity to
1:21:20send or to propagate energy into our
1:21:22patient and what we're saying for every
1:21:24decibel you send in to your patient
1:21:26you're gonna lose 0.5 to one point zero
1:21:29decibels every centimeter you travel on
1:21:32the patient and then multiply that by
1:21:35your frequency cuz frequencies actually
1:21:40some frequencies attenuate more some
1:21:44frequencies attenuate less and this is
1:21:46how this works
1:21:47higher frequencies attenuate much
1:21:51quicker than lower frequencies how do
1:21:53you know this is true anyway you have
1:21:56any examples I you know that lower
1:21:57frequencies travel farther than higher
1:21:59frequencies okay you're standing on the
1:22:07side of the road and somebody drives by
1:22:08with a really loud stereos and it's
1:22:11middle of winter so their windows are
1:22:13rolled up what do you hear bass or
1:22:14you'll hear i guessing singing you hear
1:22:18bass bass will travel down the road
1:22:21around the corner you can hear somebody
1:22:23with a loud car stereo all you hear is
1:22:28right those are low frequencies because
1:22:31they travel much farther than the high
1:22:34you see high frequencies and the reason
1:22:36being is because the wavelengths are so
1:22:38short they catch every particle on the
1:22:41way and slow down its progress whereas
1:22:44low frequencies there their wavelengths
1:22:47are so big they don't even hit half the
1:22:49particles on their way out so low
1:22:52frequencies penetrate much further than
1:22:55high frequencies and that's what this
1:22:57formula is telling you so let's let's
1:23:00let me show you an example of what I'm
1:23:02talking about so this is just an example
1:23:06don't think you got to work this in your
1:23:08head so I if I wanted to know how many
1:23:13decibels are lost in 10 centimeters with
1:23:19a 5 megahertz transducer I might write
1:23:26I'm so big okay so you would use this
1:23:29formula and between 0.5 and 1.0 is the
1:23:35average of 0.8 so if it's not given the
1:23:39average attenuation is 0.8 decibels per
1:23:42centimeter per megahertz so let's just
1:23:44use that let's say I have 0.8 decibels
1:23:47and again I said it was per centimeter
1:23:49so I said there's 10 centimeters of
1:23:51travel multiplied by 5 megahertz not the
1:23:54beautiful thing about this is we're not
1:23:56worried about units we're just be
1:23:58worried about the number because if you
1:24:00plug in the right number at the right
1:24:02units they won't it all you have to do
1:24:04is add these up so what's 0.8 times 10
1:24:110.8 times 10 nobody knows 8 x 5 which
1:24:20means 40 decibels are lost traveling 10
1:24:27centimeters with a 5 megahertz
1:24:28transducer hey so with the 5 megahertz
1:24:36we lost
1:24:38forty decimals alright so let's say we
1:24:42want to do that same problem but with
1:24:44the ten megahertz transducers so it's
1:24:46still attenuating at 0.8 decibels still
1:24:50traveling ten centimeters but now I'm
1:24:53all now scanning the patient with the
1:24:55ten megahertz transducer 0.8 times 10
1:24:58again is a multiplied by 10 we now have
1:25:0280 decibels lost so by increasing the
1:25:07frequency we have increased the decibels
1:25:10lost so that means we're going to have
1:25:14to increase our output power every time
1:25:17we use a higher frequency to propagate
1:25:21through a patient more power which means
1:25:24more intensity which means more
1:25:26likelihood of causing irreversible
1:25:28biological effects and then eventually
1:25:32we'll learn later that the FDA is going
1:25:34to have a cut-off valve that says you
1:25:37can't go beyond this intensity level
1:25:38you're gonna hurt somebody so it turns
1:25:42out the bigger the patients we have the
1:25:45deeper we have to penetrate into
1:25:47patients the lower the frequency we need
1:25:51to use to get there and what we'll learn
1:25:53out later in ultrasound is that lower
1:25:55frequencies produce ugly images we can't
1:25:58see things very well this is why large
1:26:02patients are not image very well by
1:26:04ultrasound in patients are imaged really
1:26:07well it's a concentrate off between
1:26:10frequency and iteration so attenuation
1:26:15again is the gradual loss of energy as
1:26:18it propagates so a good analogy of this
1:26:22would be if I turn down a radio and I
1:26:24turned it up to volume five right here
1:26:26and let's assume there's no walls and
1:26:29this is somewhere on the ground floor so
1:26:30I don't fall on kill myself but I start
1:26:33walking away from you halfway across
1:26:35campus would you still hear it if I'm
1:26:39all the way over by the powder Center at
1:26:41the same bomb volume as you did when I
1:26:43was in the classroom the space between
1:26:46us and this is what this attenuation
1:26:47coefficient is telling us is that the
1:26:50space between us because in Korea
1:26:52centimetres are increased distance we're
1:26:54going to attenuate more and there's
1:26:56going to be less power at the end of
1:27:00that distance so more distance more
1:27:03attenuation till lastly we get to the
1:27:05last step which is complete absorption
1:27:08there would be a point in which I would
1:27:10walk away from you far enough that you
1:27:14would no longer hear the sound coming
1:27:16out of that radio doesn't mean that the
1:27:18sound doesn't come out at radio is just
1:27:20that all the energy has been absorbed
1:27:23within the distance between us and
1:27:26that's attenuation to the point of
1:27:29absorption calculated by this formula
1:27:33the attenuation coefficient all of this
1:27:37is related to power intensity and the
1:27:41reason we need that power intensity is
1:27:44because everything attenuates everything
1:27:48reduces power and everything reduces our
1:27:54intensity in fact a normal wave form
1:28:00outside
1:28:08you
1:28:17can you hear me now my back in that's
1:28:21stupid thing alright so a normal wave
1:28:27actually looks whoops
1:28:28why is nothing coming up that's weird
1:28:33I have no function at all okay
1:28:43maybe we got it back now okay so a
1:28:45normal wave as it propagates looks
1:28:48something like this
1:28:52so if you remember amplitude or its
1:28:55strength
1:28:56eventually decreases the longer it
1:29:00propagates it gets less and less to the
1:29:04point where it doesn't exist anymore and
1:29:06at this point we call it absorption this
1:29:11entire process is known as attenuation
1:29:21right that makes sense I mean you know
1:29:27people have attenuating personalities
1:29:29right it's constantly dragging me down
1:29:31it's the point where you have no energy
1:29:33left well not even that woke you okay
1:29:38that completes Chapter two questions
1:29:50Kira Jamie are you still with us do you
1:29:53have any questions yep so next I want to
1:30:03show you the lab assignment I'm going to
1:30:05try to save some time plus I'm going to
1:30:07try to help the online students see
1:30:11physically what we're talking about the
1:30:13first thing I would like to do is hand
1:30:16out what we're what we're going to work
1:30:19with here so what I have here is roughly
1:30:24the same size waterville in this
1:30:27lettering on the
1:30:30yeah the camera let me know if I'm close
1:30:35to being enough oh okay
1:30:54so who I have a water balloon well kind
1:31:00of roughly the same size of the softball
1:31:02so I want to pass this around you're
1:31:06going to feel weight and the
1:31:08characteristics of the water balloon
1:31:11versus the softball in these particular
1:31:14areas density mass per unit volume
1:31:20stiffness how hard it is elasticity its
1:31:25ability to return to its original shape
1:31:27and how quickly it does that and it's
1:31:30compressibility can you compress it and
1:31:32how much force does it take to compress
1:31:34it got all those figured out Morgan did
1:31:40you feel I'm all ready yet okay all
1:31:42right
1:31:42so which has happened before all right
1:31:55right so looking at your lab assignment
1:32:03what we want to do is make a comparison
1:32:05of each one of these now please remember
1:32:08the piece we're not comparing the
1:32:12velocity of water because we're simply
1:32:20talking these work molecules at the
1:32:24macro level or particles at the macro
1:32:27level what were the characteristics that
1:32:29you felt or experienced with these
1:32:32objects so let's take a look for
1:32:37instance the water balloon okay so one
1:32:43let's let's talk about
1:32:44Fitness did you feel that the water
1:32:46balloon was extremely stiff not able to
1:32:49be compressed no it's not stiff so you
1:32:52would say that the water balloon is not
1:32:54stiff okay
1:32:56holding them up and feeling how heavy
1:32:58each one of them on which one was more
1:33:00dense mass per unit volume the water
1:33:04balloon or the softball which one was
1:33:06heavier water balloon had greater
1:33:09density that's right okay
1:33:11which one was more compressible water
1:33:16balloon or this one water balloon
1:33:20definitely and elasticity the ability to
1:33:23return to its original shape quicker
1:33:26which one returned to its original shape
1:33:28quicker imagine if you would buy the
1:33:31softball if we had a slow-motion camera
1:33:33and you watched it being hit by a bat
1:33:35which one do you think would return to
1:33:37its original shape quicker softball
1:33:40would okay all right so you understand
1:33:42the four media characteristics related
1:33:44to a water balloon and this softball now
1:33:50understanding which characteristics
1:33:52propagate energy better which one of
1:33:55these objects the water balloon or the
1:33:58softball do you believe would propagate
1:34:00energy better softball right okay let's
1:34:04see if that's actually true so now I
1:34:07need your help to make sure that they
1:34:08can see this so can you see the end of
1:34:13the table and what would happen after
1:34:15this happens okay so what I'm going to
1:34:19do now is see if this is true so the
1:34:31weight the only way that we can actually
1:34:32do this is hold these things still here
1:34:35right meaning I just want to hit this
1:34:36and they would roll off the table so I
1:34:38have to actually hold these still to
1:34:42create a medium and what I'm gonna do is
1:34:44hit this size of a hundred balloons and
1:34:46see what energy propagates to the other
1:34:48side and how far that tennis ball will
1:34:52roll ready you still see it okay
1:34:56make sure that I'm you were thinking it
1:35:04was gonna scratch it so did it propagate
1:35:06energy yes or no yes okay so for right
1:35:09now that is our standard so now what
1:35:12we're going to do is replace these but
1:35:15something we think should propagate
1:35:16energy better again without moving these
1:35:19and simply watching what happens with
1:35:23the same force not any more or less
1:35:27right so you thought these softballs
1:35:32would propagate energy better and what
1:35:35you just witnessed is without moving
1:35:37them they do propagate energy much
1:35:40better
1:35:40so stiffer non dense particles actually
1:35:43and those remember they're the two most
1:35:45important characteristics stiffer non
1:35:48dense particles actually propagate
1:35:50energy better and this is related to a
1:35:52higher acoustic velocity in a higher
1:35:54acoustic our propagation speed that
1:35:57being said you now have your lab
1:36:00assignment all set up for you it was
1:36:02already done for you now just fill in
1:36:04right finished at you will have to find
1:36:07a reference within your book that agrees
1:36:09with what you observed and what you
1:36:11believe and then of course as with all
1:36:14lab assignments there's conceptual
1:36:15questions at the end to see if you
1:36:17understand these concepts any questions
1:36:19before I let you go to finish this lab
1:36:24very none Jamie and Cara do you have any
1:36:30questions no okay remember you can turn
1:36:35your labs on next week there's no rush
1:36:36to get them in okay all right thank you
1:36:41for joining us we'll see you next week
1:36:42in class