A Pop! in the Night: How Sound Helps Us See in the Dark - Free Educational videos for Students in K-12

A Pop! in the Night: How Sound Helps Us See in the Dark - By MITK12Videos

Transcript


00:15	Right Welcome to the campus of M . I .
00:18	T . The massachusetts Institute of Technology in Cambridge massachusetts
00:22	you might think of mitt is a great place to
00:24	learn about Science and technology , but here's something you
00:27	probably didn't know mitt is also a great echo chamber
00:32	. In order to make an echo . We need
00:34	a source or something to make a sound and we
00:37	need to reflect it or something to bounce the sound
00:39	back to us . In this case we're going to
00:42	use this balloon as a source and those buildings over
00:46	there as a reflective ready ? Okay , an echo
00:52	is just a sound that bounces back to our ears
00:55	. When the balloon pops , waves of pressure called
00:58	sound are released into the air . In the air
01:02	. These waves travel really fast at 760 mph way
01:08	faster than your car . We can hear these sounds
01:11	either directly or after they've bounced off something sound bounces
01:17	elastically like these balls off the wall . The farther
01:22	away from the wall you are , the longer it
01:24	takes for the sound to come back . Mhm .
01:28	Mhm . We can also draw sound waves as pictures
01:32	called wave forms . In this picture time goes to
01:36	the right and the thickness of the blue shape shows
01:39	how loud the sound is over time . Let's listen
01:43	to our balloon once again this time with the picture
01:47	. Yeah , See there are two points when the
01:50	sound is loudest . These represent the balloon popping and
01:54	traveling to our ears directly and its echo . Now
01:59	to hear the echo , the sound had to travel
02:02	all the way to the buildings and all the way
02:04	back by measuring the time between the first sound and
02:09	the second , we can estimate the distance between us
02:12	and the buildings . In this case it took .2
02:16	seconds , which corresponds to a distance of about 30
02:20	m . Mhm . But what happens if we make
02:25	sounds in a different place ? Like this amphitheater ?
02:29	We can see by throwing the balls in different directions
02:31	. The sound will bounce back to us at the
02:33	same time . From all of these directions . Let's
02:37	hear what it sounds like comparing this wave form with
02:45	the old one . We can see that the time
02:48	between the balloon popping and its echo is much shorter
02:52	. 0.025 seconds , Which is about a 10th of
02:57	what we heard before . So the distance is only
03:00	about four m . Okay , what about a different
03:04	space ? Like this hallway ? This space is cool
03:07	because we have two walls that are really close ,
03:11	So the sound's gonna bounce back really quickly and one
03:15	wall which is really far away and it's gonna take
03:25	the sound a while to bounce back if ever .
03:32	Yeah , we can compare this wave form with the
03:39	previous ones and see that the sound actually does come
03:42	back . In this case it takes .4 seconds corresponding
03:47	to a distance of about 60 m . But what
03:51	if we could find a space where sound didn't come
03:54	back ? This is a recording booth which is used
03:58	to make radio pieces . The idea here is to
04:01	absorb the sound so it doesn't echo . To do
04:04	this , we have thick doors which are covered in
04:08	carpet inside . We can also see these pieces of
04:14	fabric which are gonna absorb sound the same way they
04:17	absorb the bounces of this ball . I'm gonna shut
04:21	myself inside and see if we do in fact get
04:24	no echoes . Let's find out . Yeah . Uh
04:30	huh mm mm . Okay , once again we can
04:40	look at the waveform to better understand what's going on
04:43	here . We see when the balloon pops but look
04:47	no echo . But does popping balloons all over campus
04:53	have any actual applications ? Is any of this actually
04:57	useful turns out it is both animals and humans use
05:04	echoes for a variety of purposes by sending sounds through
05:08	the water . Some animals , like dolphins and whales
05:11	can use the sound to find their way in the
05:14	dark when these sounds bounce off objects like fish .
05:17	Dolphins are able to detect the echoes and know where
05:20	the fish are . By studying how sound works and
05:23	travels through materials . Scientists and engineers are able to
05:27	use a system called sonar to find things in the
05:30	ocean . Sonar works by bouncing sound off of objects
05:34	like the bottom of the ocean and measuring the time
05:37	it takes to receive the echo just like we did
05:39	with the balloons . The closer the object , the
05:42	shorter the time . By taking many different measurements .
05:46	Scientists and engineers can even form maps of the ocean
05:49	floor in places you can't see with light . Sometimes
05:53	they can even form images of shipwrecks or fish ,
05:56	which might be similar to hell dolphin . See them
06:02	sound travels through materials and carries with it information about
06:05	the world around us . If you listen carefully enough
06:09	, you can hear the whole world in a single
00:0-1	.

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