Full transcript
0:00only getting cover all that again okay
0:03sound as we covered already for those
0:06catching up and knowing the course is a
0:09mechanical energy which means it needs
0:11particles to propagate it's good for you
0:13I guess so in order for sound to move
0:17from one space to the other it must have
0:18particles in between it to move from one
0:20space to the next example I gave was
0:23dominoes dominoes have to bounce into
0:25each other to propagate that entry
0:26across the entire line right now I'm
0:29here what evidence do we have that sound
0:32is a pressure wave never yet what come
0:38here and throw something out there yes
0:47so your body will actually vibrate it
0:51actually have you ever been in a concert
0:54and had the bass drum just hit you so
0:56hard have you ever seen those YouTube
0:58videos or people sit inside the cars of
1:00a brand-new radio and their hairs flying
1:02all over the place if particles were not
1:04interacting with that person's body or
1:07hair how in the world would that hair
1:08actually move so it's a pressure wave
1:11that pushes particles inside that
1:13confined space that allows things to
1:15move we can move things from a distance
1:17as long as there's particles in between
1:19and particles literally are anything so
1:22the dust in the air are actually
1:24particles the fact that there's
1:26particles in this room allows you to
1:28hear me if there were no particles in
1:31this room I could scream my head off but
1:33I'd have nothing to move or propagate
1:35that energy to your ear and then
1:38ultimately to your brain for
1:39interpretation of language yes I would
1:44assume so I haven't been in space lately
1:47but we do know that you can't hear in a
1:50vacuum Yeah right what's the last time
1:53you've been in a vacuum
1:55I have any of you ever been in a car in
1:58somebody's cracked the window traveling
2:01down the highway so what happens is the
2:04particles are flying out the windows so
2:06fast that it increases the space doesn't
2:08mean there's no particles in there but
2:10it does mean that there's increased
2:11space what we need is a
2:13stronger pressure ways to move those
2:15particles into each other so sound
2:17propagates so we end up I do it is
2:19really loud right but when you close the
2:23windows but stop yelling because all the
2:26particles have now recapped in now all
2:28the amplitude or pressure or strength is
2:31now hitting those particles and now it's
2:32actually knowing that it's so loud right
2:35so sound is pressure it is a
2:38longitudinal way because when we push
2:41particles in a certain direction we
2:42expect them to move exactly in that
2:44direction again like the dominoes we're
2:47going to push the first one in the
2:48direction we want energy to move and
2:50then in the direction which we want
2:51those dominoes to fall down so two
2:55longitudinal it's a mechanically because
2:58it requires particles it is oh it's a
3:03pressure wave and the amount of
3:09propagation depends on a lot of things
3:11that we're going to discuss very shortly
3:13but one of those is the strength of the
3:16incident energy so give me an example
3:21this okay let me what's a good movie out
3:24there good movie out right now a cue man
3:28is a good one okay let's just assume we
3:31all have homework tonight to go see
3:33Aquaman at the busiest movie theater in
3:36town and there's a line in front of you
3:41let's say there's ten people in front of
3:44you so your homework assignment is to
3:46take one good step backwards and then
3:50lunge forward and shove the person in
3:52front of you as hard as you write well
3:56I'm not saying it's not dangerous but it
3:58will help you understand how propagation
4:01works and amplitude specifically so what
4:03this is your inherent power is comprised
4:08of course your weight and your velocity
4:10right this is what energy comes from so
4:12the power that you have that you're
4:14going to push that person in front of
4:15you is dependent on how strong you are
4:17how much you weigh and how quickly you
4:20leap forward to create that momentum to
4:23push that person in front of you so we
4:26would expect
4:27that probably three or four or five
4:29people in front of you will then will
4:32fall into each other right now let's
4:36just say for example we decided to get
4:39somebody really strong I don't know
4:42let's say an Olympic bodybuilder or
4:45somebody and now they're gonna give it
4:46their best shot and we're gonna let them
4:49take ten full steps right into that last
4:51person do you think they'd get farther
4:52than four or five people falling into
4:54each other this is what amplitude and
4:57strength is related to it is the
4:58ultimate power to do work so with what
5:02we anticipate even the most most
5:06difficult particles to move would then
5:08also move if we apply more amplitude or
5:11strength to that initial longitudinal
5:14energy would you agree with that okay so
5:16amplitude is simply a fancy word for for
5:19strength which is also related to the
5:22power output power of your ultrasound
5:24system so when we get into the human
5:26body as we see bigger patients come in
5:29we're going to need more output power to
5:32push those particles so that they move
5:34deeper into the patient okay that make
5:38sense all right so when these sound
5:44waves move inside the human body
5:46actually when they interact with
5:47particles at all they go through
5:49something they create acoustic variables
5:53and that's this part right here acoustic
5:57variables are anything that will change
5:59inside the body after a pressure wave
6:02moves through it so imagine you're your
6:06body and inside it it's comprised of all
6:08these particles sitting at rest
6:10they're just fine sitting there and then
6:13we hit it with a pressure wave so these
6:17particles then start to move back and
6:19forth into each other in order to
6:22propagate that energy forward so
6:25immediately what happens is particles
6:27that were at rest start to move so
6:29particle motion is actually an acoustic
6:32variable because particles sitting at
6:34rest is nothing's happening but when we
6:36put pressure on it
6:37these particles start moving so particle
6:40motion and particle velocity have been
6:42used interchangeably throughout several
6:44authors of textbook so you'll see it and
6:46particle displacements on the other ones
6:48so particle motion particle displacement
6:51particle velocity are all part of this
6:53particles that rest begin to move after
6:56you push a pressure wave upon them
6:58second thing that happens is because
7:00particles will move together
7:02in one particular spot because they're
7:04literally pressed into each other
7:06particle pressure increases so that
7:10pressure increases only to the extent in
7:13which they start to relax back into
7:15their normal state and then these will
7:18relax back and then they're there and
7:19then we hit them with another pressure
7:20wave and you just see them kind of the
7:23pressure increasing and decreasing in a
7:25cyclical motion and we call that
7:27frequency eventually as they go through
7:29these cycles of compression and
7:31rarefaction which is the relaxation of
7:33the particles so another thing outside
7:36of particle motion velocity and was the
7:41other movement I don't know motion
7:44velocity was a displacement those three
7:46are kind of one acoustic variable the
7:48second acoustic barrel we discussed was
7:49pressure the next one is density because
7:52a bunch of particles are pushed in one
7:55particular spot think of the people
7:57standing in line into the movie theater
7:58you just shoved all together you got a
8:00bunch of bodies laying in one particular
8:02spot a smaller spot you remember from
8:05grade school density is mass per unit
8:07volume all right if we shoved all those
8:09people onto a scale their weight in a
8:11smaller area would be much heavier when
8:13they're all piled on top of each other
8:15rather than them separated and standing
8:17apart so particle density also increases
8:21when you put a pressure wave on us on a
8:24bunch of particles so as we discuss
8:27particle motion velocity and
8:29displacement are the same thing particle
8:31pressure is another and particle density
8:35is a third those are three things that
8:37absolutely without a doubt will change
8:39when a pressure wave is interacts with
8:41particles inside the human body there's
8:44one other acoustic variable that seven
8:47out of nine authors agree is an acoustic
8:51variable to do not
8:53and that's temperature it turns out when
8:56particles start to move back and forth
8:59and create friction inside the human
9:01body they create heat so much so that in
9:05ultrasound the number one biological
9:08effect of ultrasound is heat we actually
9:12have an entire specialty or modality
9:16dedicated to this process is called
9:18therapeutic ultrasound where you take an
9:20ultrasound probe and is specifically
9:22designed to absorb at a specific depth
9:24and create heat very deep inside tissues
9:27that allows fluid to move and sometimes
9:29muscles to relax a little bit so heat
9:34itself is in fact something that happens
9:37when ultrasound interacts with tissue
9:40two of the authors believes that it
9:43doesn't always happen and seven of the
9:47officers say there's no way that you can
9:49have these particles who are sitting
9:51still at a certain temperature and then
9:54you start to move them back and forth
9:56and greater than a million times per
9:59second and friction would not cause some
10:02temperature change so for those reason
10:05in this class and in this program we are
10:08going to say that temperature absolutely
10:10is a fourth acoustic variable okay
10:14everybody okay with kusa variables but
10:16they are yes yep well let me let me try
10:21to simplify those let's we'll say
10:23particle pressure is one particle
10:27density it's another temperature is a
10:35third and then depending on which author
10:40you read particle velocity motion and
10:43displacement are all the same thing
10:45that's the fourth everybody okay with
10:49that displacement business yeah so
11:01we discussed the last couple weeks
11:03propagation is simply a fancy word for
11:05movement right once we start a pressure
11:08wave in this pressure wave on the
11:09outside of the human body starts
11:11interacting with particles inside the
11:12human body
11:13these particles move or propagate energy
11:17by bouncing back and forth in these
11:20pressure waves they do that at certain
11:24frequencies remember we said that
11:26particles will go through a cycle that
11:28cycle is known as a compression and
11:30rarefaction wherein fracturing just a
11:32fancy word for relaxation once it
11:35completes that one cycle we then figure
11:37out how many times it does this per
11:40second an in diagnostic ultrasound those
11:45frequencies are typically one to ten
11:47million cycles per second it's a lot
11:50which is also why some people say
11:52temperature has to be an acoustic
11:54variable because there's no way you can
11:55have something vibrate at 10 million
11:57things 10 million times a second and not
11:59create friction enough for heat the the
12:04other thing that you need to know is the
12:06different kinds of frequencies and their
12:09designation so first of all diagnostic
12:11ultrasound is typically anything above 1
12:13million Hertz infrasound is anything
12:18below 20 Hertz this is below the human
12:21audible range you can't you can't hear
12:25it but you can feel it
12:26the military's actually created sub
12:30frequencies on the on the field where
12:32they can send off a sub frequency sound
12:37wave and it makes their enemies lose
12:40their bowels right on the field you can
12:45you can feel sub frequencies in fact it
12:47was very popular in the 90s some of the
12:49CDs that you know 90s CDs we said it's a
12:53track in the 90s you you could buy CDs
12:57and by listening to the song years your
12:59body would vibrate at different
13:01frequencies than the sound actually came
13:03out and there's actually a warning
13:05signal on these CDs stating that it
13:08contains sub frequencies and may
13:09completely destroy your stereo
13:11completely that's stuff you you never
13:13heard of this
13:14I'm guessing by the blank stare it's
13:16never heard of it go buy a 90 CD turn it
13:19up real loud and you'll feel your body
13:20literally vibrate at different
13:22frequencies it's very weird
13:25so some frequencies anything below 20
13:28Hertz the human audible range is 20 to
13:3120,000 Hertz 20 Hertz is like the low
13:34base stuff you hear the 20,000 Hertz is
13:36the high hisy stuff that you hear and at
13:4420,000 and 1 Hertz you're technically
13:46into ultra sound that is beyond the
13:49human audible range dogs can hear up to
13:5340 hurt 40,000 Hertz and again
14:01diagnostic ultrasound doesn't start till
14:031 million Hertz everybody got that down
14:06good all right here oh really
14:16here's my compression and rarefaction
14:19again what we see from this particular
14:21drawing is the compression cycle as our
14:24initial initial push of particles
14:27together it is your speaker so to speak
14:31that literally pushes particles or word
14:33so that particles thing can propagate
14:35across a room and then they interact
14:38with your ear because all particles do
14:42move into each other and they do
14:44eventually relax back to their normal
14:46state after they start in their original
14:48state and they compress together related
14:51to the amplitude or strength of that
14:54initial push or longitudinal energy they
14:57will come back to their original state
14:59but they kind of bounce back and forth
15:01they don't really like they don't just
15:03push forward and then go back to the
15:04original state they kind of bounce back
15:05and forth so then there's this
15:07relaxation part of the cycle from the
15:11beginning of the compression to the end
15:12of the relaxation or rarefaction that is
15:15known as one cycle
15:20and frequency is defined as cycles per
15:28second how many
15:39we kind of jumped the gun a little bit
15:40on this one we did say that there that
15:43sound is a longitudinal wave simply
15:45meaning that the energy moves in the
15:47same direction of its incident energy
15:48that's different than transverse waves
15:51in transverse waves the particles move
15:55perpendicular to its incident energy and
15:58I think a great example it might be in
15:59your textbook is if you drop a stone in
16:02the water the energy is going into the
16:04water yet the waves actually go across
16:08the surface of the water which is 90
16:10degrees to its incident energy that's
16:12considered a transverse wave these types
16:14of waves do occur in the human body but
16:17they're kind of rare they occur when
16:19there's a huge velocity mismatch
16:22typically occur in bone plaque any type
16:29of stone kidney stone gall stones they
16:34also occur in metal objects such as
16:38surgical staples and like mitral valves
16:45that have been replaced with metal clips
16:47and things like that so these things we
16:50do have transverse waves but they're
16:52pretty rare and they're just due to a
16:54dramatic velocity mismatch between bone
16:57and steel versus soft tissue bone has a
17:01velocity of 4080
17:04meters per second and as we learned
17:06today soft tissue has a velocity of 1540
17:11meters per second all right
17:13so it's roughly four times that of soft
17:16tissue and because there's such a
17:18dramatic velocity mismatch it doesn't it
17:22can't go through it at that kind of
17:25speed so it literally shears across the
17:27stur surface this is why transverse
17:30waves are also called shear or stress
17:31waves inside the human body any
17:40questions on that so far yeah I want to
17:51cover this
17:52first and then we'll move on to echo
17:54ranging all right so wait properties if
18:02we look at an ultrasound wave it looks
18:12you
18:37can you hear me yeah okay all right
18:40that's weird I don't know what happened
18:42there and now my look is all different
18:45so all right so hopefully we're back on
18:53track
18:53all right so a wave looks something like
18:59this there we go
19:02so in an ultrasound wave or a pressure
19:08wave we have you can see multiple cycles
19:12in this case we've got one two three
19:13four cycles here that is for compression
19:17zones and for relaxation so this is a
19:19four cycle what we call pulse and in
19:27that four cycle pulse we can actually
19:29measure from the beginning of one
19:32compression to the end of its complete
19:34cycle that in distance is known as wave
19:39length so the distance in one wave is
19:44simply how the distance of one complete
19:49cycle additionally we can also use that
19:52same measurement to figure out how long
19:54in time it takes for that one cycle to
19:58occur and that's known as period which
19:59is represented by a funky T so these are
20:06different ways of measuring how long it
20:09takes for one cycle to occur in time
20:11which is period and what is the distance
20:14it takes for one cycle which is our wave
20:17length we have different formulas to
20:19represent this so let's take a look at
20:22those so or period that funky T is equal
20:32to one over the frequency it is a
20:34reciprocal of that's frequency by the
20:37way there one over the frequency and
20:43conversely frequency is equal to one
20:46over the period
20:54the wavelength has several different
20:57ways of looking or calculating it and
21:00this is one of those I mean you can see
21:03the formula which velocity equals
21:07frequency times wavelength which can be
21:10knitted manipulated to solve for
21:12wavelength and/or frequency we'll look
21:14at those next week I want to get to
21:16frequency and period first and then
21:21we'll go to echo ranging and then we'll
21:23cover the other formulas next week so go
21:27here here and let's cover some of these
21:31things so again period equals one over
21:37the frequency and let's say we wanted to
21:40know what the period was of let's say a
21:44two megahertz transducer now I'm not
21:48gonna have you work this one because I
21:49want to show you how to go about doing
21:51this so setting it up period equals one
21:56over that frequency in order to do this
21:59you want to get the units all the way
22:02out to one over seconds every time
22:04because when you divide it out you'll
22:07end up with one over one over seconds
22:09which will be the same as seconds you
22:10have a good time frame otherwise it's
22:12gonna be something kind of crazy so
22:14dividing this out one two megahertz
22:17would actually be two million one over
22:20seconds there really is no shortcut to
22:24do this so we're going to actually
22:25divide two million into one and of
22:33course you figured out by now that two
22:34million does not go into one doesn't go
22:37into ten a hundred a thousand ten
22:39thousand a hundred thousand 1 million
22:42but it will go into ten million two
22:44million will go into 10 million evenly
22:46five times
22:48so now preserving our decimal place here
22:50we simply count the zeros one two three
22:53four five six so we end up with one two
22:57three four five six zeros and a five I
23:00remember because it was one over
23:02one over seconds that is seconds and
23:05there is our answer
23:09everybody okay with that good because
23:12it's not your turn all right so tell me
23:17again the period if our frequency is
23:21five megahertz let's give it a shot and
23:24then we'll see where we're at
23:32welcome Patricia I didn't see you there
23:34okay so it doesn't go on to one 110 100
23:57sorry thousand ten thousand a hundred
23:59thousand 1 million but it will go into
24:02ten million two times right everybody
24:05have that now the question is how many
24:07zeros one two three or five six didn't
24:15have that right right three sweetie has
24:17ten million okay so one two three four
24:21five sixty rose and the two and it does
24:24come out two seconds how do we do good
24:28okay
24:29let's flip it upside down then let's go
24:32let's calculate frequency then and let's
24:36say the period is point zero let's do
24:40one more zero one milliseconds remember
24:52take it out two seconds first
25:08like I mentioned before you want to take
25:11this out two seconds first because then
25:13you'll end up with one over seconds
25:15which is actually first which is
25:16actually a frequency so converting this
25:20milliseconds into seconds it's going to
25:23be actually smaller it's a big second by
25:25three decimal places so this is going to
25:27add three more zeros we end up with one
25:30two three four five six zeros and one
25:33second one Hey so now all we have to do
25:38is divide that mess into one and we're
25:40good right so again we're going to use
25:43our techniques we learned a couple weeks
25:47ago about how to deal with ugly-looking
25:49decimals and dividing them out and I see
25:52a 1 in my denominator so I'm going to
25:54get there so I'm gonna go ahead and add
25:551 2 3 4 5 6 7 decimal places here which
26:01means I have to add 1 2 3 4 5 6 7
26:05decimal places there 1 2 3 4 5 6 ok zero
26:14zero zero zero zero
26:16so yeah that's three here that's 10
26:20million isn't it ok so now I have 10
26:24million divided by one second so right
26:32you got it right so you ended up with 10
26:35million Hertz or ten acres yeah
26:59good Emily you good all right so let's
27:07do another one of those let's say I want
27:10to know the frequency if the period is
27:15let's do a point oh one microseconds all
27:24right where's me all right so we're
27:27gonna convert this into seconds first
27:28microseconds is very small we're going
27:30to make that six decimal place as
27:32smaller is a huge second so one two
27:35three four five six and we have all
27:38these zeros for an ad in front of us so
27:40we have one divided by point one two
27:42three four five six zeroes plus the
27:45original one and that's in seconds right
27:48so it looks like most of you did this
27:50right you went ahead and add in one two
27:53three four five six seven eight
27:56which means we have to add one two three
27:59four five six seven eight and we have a
28:04bunch of zeros we got to fill in here so
28:06I got three there and three there so it
28:10looks like 100 million that's million
28:15divided by one second or 100 million
28:23herbs or 100 megahertz it's like most of
28:30you got that wrong no I'm just kidding
28:32just alright so I want to show you get
28:36different way about doing this let's
28:39take this exact question was point O one
28:42let me see then go all the way back rid
28:45of all my writing go back to the
28:47original question I know right oops only
28:55too far right okay so here's our
28:59original question melee actually has a
29:01way of doing reciprocals that is fairly
29:03easy to do we actually see it in the
29:05book No okay so he said if you break
29:09down the components
29:10of what this is and simply take the
29:13reciprocal of each component you'll come
29:15up with the right answer so let's take
29:17point zero one micro and second those
29:22are the three components of this
29:24particular
29:33you
29:52all right just to be clear
29:55how does Sun Patricia can you still hear
29:58me you can hear me okay good
30:03sorry about the Hawaii keeps kicking me
30:05out okay
30:08there we go all right yeah I disappeared
30:13for a minute I don't know why it's
30:14kicking me out and let me get back to
30:17where we were
30:18okay here we are this is the point it
30:20was trying to make okay so we take the
30:22reciprocals of each three of these
30:23components the reciprocal 0.01 as you
30:25remember from our first lesson is one
30:28over point O one correct the reciprocal
30:32of micro is you remember is times ten to
30:35the negative six what would be the
30:36absolute opposite of that 10 to the
30:40positive six which we know as what what
30:44is that prefix in the metrics mega right
30:48and then seconds the inverse of seconds
30:52is one over seconds and one over seconds
30:55is also known as Hertz right so taking
30:59this a little bit further now
31:08you
31:25Ernest like just making that line like
31:29kicks me out well I could probably do it
31:35again I've done it twice now last
31:36co-writes alright so one divided by 0.01
31:39if we just add one two decimal places
31:44here on one two here
31:45that's when home 100 over 1 or 100 we
31:50already said that the inverse of micro
31:52was mega and we already said the inverse
31:53of seconds was hers right so what do you
31:58have on the answer for the bottom 100
32:01megahertz that's being pretty easy
32:06didn't it you're mad because it's easier
32:11okay let's try another one that's let's
32:14say we have one well let's just try this
32:18one microsecond what is the reciprocal
32:21I'm gonna do it
32:22maybe I'll try it I'll do it what Kendra
32:25set up try it backwards that worked
32:28about kicking me out
32:29yes apparently if you right swipe you're
32:34done okay got it
33:05you don't mean you don't can't be
33:10confused or I didn't explain it right
33:28all right what's the reciprocal of 1
33:34which is 1 right
33:36what's your separable Kol of micro Megan
33:41right did that already and the
33:43reciprocal reciprocal of Hertz or sorry
33:45seconds okay it's hers right so 1 mega
33:50Hertz is the answer
33:52wait so what was this second so you said
33:541 over 1 and that's going to be the one
33:56that works and then you said the micro
33:59and then micro is times 10 to the
34:02negative 6 the absolute reciprocal to
34:05that is times 10 to the positive 6 which
34:08is mega right let's try another one but
34:14this time let's calculate a period based
34:17on the frequency so let's take 2 mega
34:23Hertz and what is the reciprocal oh no
34:28it's gonna do it again you see that blue
34:31thing it's gonna swipe me out if I don't
34:34go back that's what happens I do that
34:38swipe in it like I'm gone I don't know
34:43yeah it says an arrow but every time I
34:45make that swipe that blue arrow comes in
34:47and then kicks me out because my MacBook
34:54does that yeah but but when it does that
34:57it kicks me all the way out to the
34:59beginning of this tab it doesn't take me
35:00to another tab seems like it would so at
35:17the end I'm gonna do a swipe like this
35:30all right what's a reciprocal you can do
35:33we have to do it all the way out or do
35:34you already can you do it in your head
35:38okay let's 1/2 right which in a decimal
35:43is what 0.5 and then mega the reciprocal
35:48negret make is what the mucin micro
35:54right the reciprocal of hertz which is 1
35:58over seconds what's the reciprocal of 1
36:00over seconds 0.5 micro seconds is the
36:04answer to easy right yonder like that
36:13every time here's the thing for period
36:15and frequency as well as pulse
36:17repetition period and pulse are / -
36:18repetition frequency which we've been
36:20talking about later any time we're
36:22dealing with reciprocals this little
36:24grid method that merely came up with
36:26actually works very very well and it's
36:28easy just easy I mean you can literally
36:31do it with anything so let's say I had a
36:341 milli second let's just do that one
36:38real quick what's the reciprocal of 1
36:41milli second backwards
36:55got it Anna you look bored huh
36:59you look bored it's too easy this
37:02ultrasound physics piece of cake
37:09everybody have an answer now yeah so out
37:13loud what is it that's right one over
37:19one that's right one meal a Mille as you
37:24remember was 10 to the minus 3 but pick
37:2610 to the positive 3 was kilo and
37:29seconds is 1 over seconds or Hertz so 1
37:33kilohertz that's the answer so easy
37:36right test could we write it like 1
37:38kilohertz or do you want it written down
37:41I want you to answer a B C or D circle
37:47the right one yeah I do it
37:49alright so we feel pretty good about
37:51frequency period right the time it takes
37:55for one cycle to occur versus how many
38:00cycles occur per second which is the
38:02definition of frequency yeah we feel
38:05pretty good leaving it here and then
38:06moving on to this thing I know it
38:12briefly touched on it before but in
38:14ultrasound it's a little bit different
38:16and that is often times we're finding
38:19trying to find the distance to the
38:20reflector which is often times this the
38:28distance to the reflector is how long it
38:30took to go out and back divide it in
38:33half because the reflector is half the
38:36total distance traveled in an echo
38:38remember echoes sound goes out it
38:40bounces off and travels all the way back
38:43and as we understand that we can
38:46manipulate this formula either way so
38:49there's different ways of looking at
38:51this formula so for example if I said if
38:53I said how far away is an interface if
39:07the
39:09eko time that's an e by the way is 0.01
39:16milliseconds seconds stereo that's okay
39:24so let's look at what this problem is
39:26trying to tell us it's saying how far
39:29away distance we know velocity if it's
39:33not given its going to be fifteen forty
39:35meters per second which is the velocity
39:37in soft tissue and the time is 0.01
39:42milliseconds so if we calculate this out
39:46let's see if I can so I will mmm
39:59actually don't know how to get out of
40:01this mess
40:01I'm told you're here so I'll put it
40:04together here so D equals fifteen forty
40:10meters per second multiplied by 0.01
40:14milliseconds hey so I have to convert
40:20either 0.01 milliseconds to seconds or
40:24convert 1540 meters per second into
40:27meters per millisecond before I can
40:29multiply this because our units don't
40:30match so I'm going to convert 0.01
40:34milliseconds into seconds which would be
40:36three decimal places smaller so I have
40:40one two three four one seconds
40:43multiplied by fifteen forty meters per
40:46second and all I have to do is go one
40:50two three four five and then take away
40:54one two three four five I end up with
40:57point O one five four meters per second
41:00multiplied by one second or 2001 five
41:09four meters now what does that actually
41:12tell me
41:13it says the echo time to go out and back
41:17echo time means to send and receive
41:22this one is actually both the echo time
41:25says that echo went out and back so this
41:28distance is actually out back my
41:31question was how far away is the
41:33interface correct so we'd have to divide
41:36this answer by two in order to get the
41:40distance to the interface so to make my
41:47math easier I'm gonna turn that into
41:49millimeters which would be fifteen point
41:51four millimeters divided by two which
41:55would end up by being seven point seven
41:59millimeters that's the distance to
42:02interface we got to do that again okay
42:12all right so let's take the same what oh
42:18I was so close to being millimeters good
42:44so let's go back to our original
42:45question how far away is the interface
42:49that the equity is let's change that oh
43:04let's see what do we want to make the
43:07echo time let's make it ten milliseconds
43:26right or wrong we have an answer
43:28okay so I started setting it up here
43:32again we have fifteen forty meters per
43:35second multiplied by ten milliseconds
43:37that's just the problem we're dealing
43:38with so I converted our milliseconds
43:41into seconds which turns it into 0.01
43:44seconds I would go ahead and add one two
43:48decimal places here and take two away
43:50from here turning into fifteen point
43:52four meters per second multiplied by one
43:55second so we would end up with whoops I
44:00can't write up there can i I'm running
44:04out of space
44:09I've tried down here so we would end up
44:12with the 15 point four meters but
44:21remember because that's echo time that's
44:24out and back and I want to know how far
44:26where the how far away the interface was
44:28so I'm to divide that in half which
44:32would end up by being seven point seven
44:34meters which is not the same as seven
44:37point seven millimeters which we had for
44:40our last answer in millimeters this
44:45would be 770 one two three no it would
44:53be bigger than that 7700 okay got it
45:08feeling pretty good about it
45:11okay let's try different let's let's
45:17just understand how far a wave travels
45:27in soft tissue in one second so in this
45:49case you would simply set it up the same
45:53way how far which is distance equals
45:58fifteen forty meters per second
46:01multiplied by one second three couple
46:04things that are nice about this one you
46:06don't have to divide it by two because
46:07you're simply traveling you're not
46:10figuring out the echo time and how far
46:12away the interface is - there are no
46:14metrics conversions on this one and
46:16furthermore your math is easy going back
46:19to this thing I keep saying is that if
46:21your math and if you've mastered your
46:22math and metrics this class becomes so
46:24easy right so fifteen forty meters per
46:30second multiplied by one second is one
46:32thousand five hundred and forty meters
46:34done right okay so it's not the physics
46:41it's not choosing the right formula it's
46:43not putting in the information correctly
46:45it's not even deciding whether or not I
46:48mean you you decided that metrics
46:50conversions did not have to happen in
46:51this case what throws you off is
46:53actually doing the metrics conversions
46:55and actually doing the mass because when
46:57there's no math or metrics conversions
46:59to happen you do everything else
47:01correctly which makes this really easy
47:04and that's all physics is finding the
47:07right formula plugging in the
47:09information and coming up with an answer
47:12right everybody feel pretty good about a
47:17car engine formula - the math and the
47:19Metrix okay alright um we need to get to
47:24lab just for like an hour late so are
47:27there any questions
47:28dying questions you have to know before
47:29we go to lab no let's review lab real
47:34quick is there some tricks about lab 3
47:39here's the here's the primary problem
47:44and it says last week I use two
47:46stopwatch to measure the echo time of my
47:48snare drum in the hallway used outside
47:50the classroom which is 80 meters long
47:52the average echo time was 10
47:54milliseconds use your understanding of
47:56the echo ranging formula to prove or
47:58disprove my findings
47:59remember this is echo was heard in air
48:01what I mean by that is that the velocity
48:04in air is not the velocity and
48:06soft-tissue typically you will find the
48:08velocity and air to be somewhere around
48:10330 meters per second part of this lab
48:13was having you look that up but since
48:16we're running so far behind I'll just
48:18give it to you next the next big thing
48:22about this is figuring out how you're
48:23going to just prove my son my findings
48:26so I'm going to give you sort of some
48:29direction it doesn't matter whether you
48:31prove it by proving that my time is
48:33wrong or that my distance is wrong but
48:36using my numbers as long as you use 330
48:39meters per second you will find that it
48:41won't that you will figure it out one
48:45way or another you can choose solving it
48:47by distance time or velocity and you'll
48:51come to the same conclusion whether it
48:53actually happened or not okay the second
48:57part of this is understanding it
48:59conceptually to understand well if
49:02distance increases and velocity rates
49:04and change what happens to time okay
49:07through this you would use the echo
49:08ranging formula to say if what happens
49:12to time because that's its question what
49:14happens to time understanding that the
49:16formula looks something like that if
49:18distance decreases what happens to time
49:21and that's the way you would tackle the
49:23conceptual part of the questions the
49:25mathematics is the top part the
49:26conceptual part is the bottom part if
49:29you master these you should be able to
49:30answer any
49:31next us regarding tech arranging all
49:34right any questions before we go to lab
49:38wait once I yes
49:423:31 is also used 330 is more of a
49:46ballpark Patricia it what it basically
49:49depends on is temperature so depending
49:53on the room temperature it can fluctuate
49:54up to 20 degrees to if it's cold versus
50:00warm so 3:30 is fine 331 is also fine
50:03347 yeah that's also been used just
50:06depends on again the temperature in the
50:08room so any one of those are fine to use
50:10you'll still be able to answer the
50:13question correctly any other questions
50:15before we go laughs really
50:23me too I want that to happen too that's
50:26right there is no shortcut everybody can
50:29see a shortcut there are no shortcuts
50:31all right sign it off then I