Main content

### Course: Class 9 Physics (India) > Unit 5

Lesson 4: Ultrasound# Echolocation & S.O.N.A.R

Let's learn how animals and ships use echoes to 'see' the world around them. Created by Mahesh Shenoy.

## Want to join the conversation?

- If humans can't hear frequencies above 20,000 hertz, then how Daniel Kish ecolocate? I watched one of his videos of him doing it but failed to understand how.(1 vote)
- Daniel Kish started practicing since he was young. Anybody who would learn this skill earlier would be able to do this.(2 votes)

## Video transcript

in around 1800s scientists were very curious to find that bats could fly and avoid obstacles in complete darkness do they have super sensitive eyes no because they found that even the ones which were completely blind could also do this suggesting that they were not relying on their eyes however surprisingly when they put a plug in their ears temporarily making them deaf they failed miserably what so does this mean that bats see with their ears well kind of after a lot of research people found that bats continuously emit pulses of sound of ultrasonic frequency and ultrasonic means a frequency higher than 20,000 Hertz and because humans can hear up to a max of 20,000 Hertz you and I cannot hear this sound and thank God for that otherwise can you imagine how noisy it would be around bats but how does this help well when this sound goes and hits some obstacle it reflects back and the bats can hear this reflected sound in other words they can hear an echo of their own voice now depending on how long it takes for these bats to hear their own echoes they can estimate how far that obstacle is for example if it takes a long time for them to hear their echoes it means the obstacle is far away so no worries they can chill on the other hand if it takes a very short time for them to hear their echoes that means the obstacle is very close to them so since they're using echoes to locate how something is we call this technique as no surprise echolocation and bats are so good at echolocation they can even tell whether these echoes came from a large tree or from a tiny mod their favorite insect to feed on and a fun fact about moths since they're hunted by bats using this technique using these high-frequency sounds their ears have evolved to be able to listen to these high-frequency sounds and so whenever bats are in pursuit of them they immediately get to know and they try to evade them and bats aren't the only ones that use echolocation turns out certain sea creatures like dolphins or whales also use them the thing is underwater you can't see very far away you may have noticed this if you looked at some underwater footage you can see things which are close to the camera but things which are far away you just can't see and that's because light gets very easily absorbed by water so light can only travel a small distance before getting completely absorbed however sound can travel a lot farther before getting absorbed and that's why these animals have evolved to use sound and their ears rather than their eyes to navigate underwater and for this very same reason even the ships and submarines have stolen this technique to navigate underwater they're equipped with devices that can generate high frequency ultrasounds and which can also receive these reflected echoes and just like with the bats by calculating how long it takes to receive that echo they can calculate how far the object is and these devices are called sonar it's an acronym for sound navigation and ranging which basically means we are using sound to navigate or to move and avoid obstacles and ranging meaning to figure out how far something is so while bats and dolphins have naturally evolved to use sonar we use science to do the same thing in fact in this technique just by using the formula of speed we can calculate exactly how far something is so let's take an example so let's imagine we are inside this ship and we want to calculate how far the floor of this ocean is from our ship to do that we will send an ultrasound and let's say if we receive it after a time of four seconds the speed of sound in water is something that people already know it turns out to be roughly 1500 meters per second and so using this information we want to calculate how far the ocean bed is from the ship let's call that distance as D so how do we do this well we know the formula to calculate speed speed equals distance by time so using this formula let's see if we can calculate what D is in fact can you try and do this yourself first pause the video and see if you can substitute in this formula and calculate what this distance is alright since it's the sound that is traveling the speed over here will be the speed of sound so if we substitute for speed we will get 1500 meters per second that equals distance now distance traveled by the sound is not d because notice the sound goes down and then comes back up again so the total distance it travels is 2 names this value to D so it travels a distance of two D and we know the time it takes to travel the distance that is four seconds now from this all we need to do is do some algebra and we can calculate what D is again if you're not done this before great idea to pause the video and see from here if you can calculate what D is all right let's do this so if you simplify 2 goes 1 times 2 goes 2 times so let me raise the two from here 2 goes to x over here 2 seconds now since I want to calculate D I want to get rid of this 2 seconds I will multiply by 2 seconds on both sides of the equation so I multiply by 2 seconds here I will also multiply that by 2 seconds over here and so the 2 seconds will get divided over here notice the seconds cancel out and what I'm left out on the left hand side is 1500 times 2 15 times 2 is 30 so this will be 30 and then two more zeros 3000 meters equals Rd so the floor of the ocean is 3000 meter below the ship and this is how we can use sonars and the formula of speed to calculate how far something is so what did we learn in this video we saw that echolocation is a technique used by bats and whales and ships to calculate how far something is this is also called a sonar and how does it work we send out a high frequency sound and calculate how long it takes to receive the echo then we can use the formula of speed and figure out how far the object is and guess what turns out that there are some blind people who have learned how to make sounds from their mouth echolocate that's pretty cool isn't it