Can you Communicate in Outer Space?
Now the question really is does sound require that there is air around us to propagate it? Now, after having understood the previous module, you know that it’s a very silly question to ask because if I pluck something and if there is nothing to compress and expand, how exactly we be…our ears be able to hear sound? But just for a purpose of excursion into thought, let’s really being to see what would happen? Because if you already understand what sound is, then you really know that the really keen amongst you, who follow the previous bonus section. You know that. It’s a mechanical wave, right? It requires something mechanical to oscillate for it to propagate. It means that if that mechanical thing was removed, in this case, air…it wouldn’t be able to propagate at all. So if you want to understand sound as a mechanical wave that needs a medium, your understanding will be a lot more than if you remember. Sound requires air to travel. If sound is…There is no air…sound won’t travel. As if its very specific for sound and for air. Not really. For any mechanical wave, you need a medium. Right? Otherwise you could do a Bell Jar experiment…you put a Bell Jar and you put a little alarm clock into it and suck out all the air from the Bell Jar and then what happens in that you begin to…you don’t hear the sound of the Bell Jar…sound of the alarm anymore. Wow! That must be surprising, right? You don’t know how sound works that would be surprising for you. But now its not going to be surprising, right? Now if…the example really is – if somebody somehow were really sarcastic and began to remove all the air from this room, what would begin to happen is in some time (mute expression) and that’s what (mute expression). And the sound is coming back slowly, what will begin to happen is you are going to begin me hearing again. So kind of what we require for sound to propagate is air or some other medium, which bring us to our next question. Can sound travel through other media like liquid or solids? Cant’ it? Why can’t; it? Such a question. So before we go there, we need to ask how does sound really propagate itself. Right? How does sound move? Because we know that if I pull a string like this or a rope ..it..the wave it propagates exact way while the rope goes up and down is the Transverse Wave. How exactly does sound do that? So in air, we know its compression and rarefaction…all the air molecules are vibrating this way…so it’s a longitudinal wave. Awesome. So, our books always say that sound waves are longitudinal…no more questions asked, right? But it turns out that the really the keen amongst you will ask that question. Always? Because whenever the word always hits you, it’s a good question to ask – Really? Because it is very unlikely that always something is true. So it’s a good place to begin to feel doubtful. And if you word out, you are right. Because sound doesn’t always travel longitudinally. You have tried to spread solids…sound through a liquid or a gas, it would always be longitudinal. Why that is going to be true…will tell you in some time or you will find out if you are really curious. But when you take sound into a solid…so can sound travel through a solid? Yes, of course. You create a vibration…in this case, if it’s a solid… instead of air molecules compressing and relaxing and things like that…the parts of the solid are going to do that. Now the interesting thing here is in solids, sound can travel both as a longitudinal and as a transverse wave. Because solids allow transverse waves to pass through them. They are suitable for transverse waves. Why exactly? They have something called elasticity…solids have a much higher elasticity. They can withstand an attempt to change their shape, right? Solids kind of withstand that ..if you try to change the shape, they kind of withstand that. They resist a change to the shape. But do liquids do that? You pour a liquid in a container, it takes a shape of that container. Poor gases, you don’t have to even ask. Right? They don’t really resist any change. So in that way solids are different than liquids and gases. Therefore, in solids sound can even travel as a transverse wave.