What's the scientific reason for echos?

Answer 1

A mismatch in the impedances (either mechanical if sound echo or electrical if electromagnetic reflection) of the medium the energy is passing through and the medium it encounters. The mismatch prevents all the impinging energy from being absorbed.

Answer 2

Sound is a compression wave transmitted through the air: it compresses and expands the molecules it travels through like a Slinky. When a sound wave comes to a boundary, it some portion of it is reflected. If it's reflected on a surface a great distance away and not lost as it travels back, the sound is heard much later as an echo.

Answer 3

Sound waves bounce off solid objects and reflect back to your ears. The echo is delayed slightly depending on how far away the object is.

Answer 4

go to a pool and push a wave of water w ur hand. Watch the wave go to the edge of the pool and then bounce back to you. Same thing, exactly.

Answer 5

sound waves bounces off an obstacle and virbrates, causing echoes.

Answer 6

An echo is an eerie phenomenon that can occur under certain circumstances, and is caused by several conditions which must be just right. Let's look at what causes an echo!

Echos happen because sound bounces off things. You probably knew that already. But something else has to happen as well; just bouncing won't make an echo. After all, you don't hear an echo when you yell in your bedroom, even though the sound is bouncing off the walls.

The first requirement for an echo is distance. Sound travels fast ... about 300 metres in one second. A really good echo will return to you after several long seconds ... that's what makes it eerie. For our purposes, let's suppose that any sound that returns within half a second will overlap with your own voice and not make a distinguishable echo. So how far must an echo travel in order to return at least half a second later? Remember that it must go out and then come back to you. At 300 metres per second, or 150 metres per half-second, it needs to travel at least 150 metres in total ... or 75 metres out and 75 metres back.

As a result, to get a good echo, the sound must bounce off something at least 75 metres away. Otherwise, it will return in less than half a second, and won't make a good echo.

But there has to be more. You can yell all day at a building 75 metres away and not get an echo. What has to happen next is that a lot of the sound coming from you has to be made to bounce back. Notice that the words 'a lot' are underlined. Here's what happens under normal circumstances: The sound leaves your mouth, and travels for a while before it hits something. But sound doesn't travel in a straight 'beam' ... it comes out of your mouth and spreads in all directions. Only a little bit of it actually hits the building you're yelling at:

If the building is too small, or you don't yell very loud, very little of the sound from your voice will actually hit the building. So it doesn't matter whether it bounces back or not ... very little of that little bit of sound is going to bounce, and you probably won't hear an echo.

It's even worse than that. Many surfaces don't bounce sound evenly if they're rough. Whatever little bit of sound actually reached the building gets scattered in all directions! And only a tiny bit of that makes it back to your ear!

So if sound is scattering everywhere, how is it that we ever manage to hear an echo??

In order to get an echo, sound must follow a rule of reflection that says that it will bounce at the same angle at which it hit. If you expect any sound that hits the wall directly to bounce straight back to your ear, it must follow this rule. But it will only work if the bouncing surface is smooth. That's the second requirement for a good echo.

With a smooth surface to bounce off, less of the sound will scatter, and more will come back to you.

But you probably still won't hear an echo. Something else has to happen ... there isn't enough sound energy coming back to your ear for you to be able to hear it. The echo will be too faint to hear, because it's being drowned out by all the other sounds from all around you. The world outside is full of stray sounds ... wind, animals, birds, traffic ... enough sound to drown out that tiny echo returning from the wall.

You could hear that echo if somehow all the other sounds except the ones coming directly from the wall could be silenced. Can that happen? Yes it can. Those sounds could be absorbed and never reach your ear if everything around you had a layer of sound-deadening insulation all over it. That way most sounds from around you would be absorbed ... it would be very quiet ... except for that tiny echo coming directly from the wall, which you will now be able to hear!
What is it that acts as a sound absorber and blankets everything? Why, snow, of course!

You've probably noticed that it is very quiet outside after a heavy snowfall. That's because most of the sounds that would normally reach your ear are being absorbed by the layer of snow. And that's the perfect time to hear an echo in your own yard! Shout at a building across the yard. The only sound that gets back to your ear is the little bit that came from your voice and managed to bounce off the wall and head straight back to your ear. And you can hear it!

But there's still more. There has to be. In summer, you won't hear that echo in your yard ... too many other sounds! But you can hear echoes in summer, in certain places. What makes an echo audible if there isn't any snow?

What we need is some way to amplify the sound. If we could get more of it, we'd be able to hear it, even on a noisy summer day.

What happens is that the sound from the wall that doesn't bounce directly back to your ear has to be given a chance to get there anyway, by bouncing again! What you need is several walls or other flat smooth surfaces, that will bounce more of the sound towards your ear.
Let's look at a situation where there are several such walls:

The sound that bounces directly back is now accompanied by more of your voice ... that bounced off other walls back to you (1) ... and more sound that came from the original wall by way of a bounce off a second wall (2). If these other walls are situated just right, a lot more of the sound will arrive back at your ear ... enough to hear the echo even on a normal summer day.
The walls inside a big building work especially well (big, because the sound has to travel about 75 metres, remember?) but the building must be mostly empty so there is nothing in the way to absorb the sound. Smooth rock works well, especially in caves, where (because of the enclosed shape) almost all the sound will bounce back. Sides of a valley work too, although too many trees will absorb a lot of the sound.

Here's a summary, then, of what conditions you need in order to have an echo:

1. The sound must travel a fair distance. We're suggesting at least 75 m,
although you can hear echos from shorter distances under the right conditions.
2. The sound must be able to bounce back. It must hit a flat smooth surface somewhere.

To be able to hear the small amount of returning sound, this also must be true:

3. All other sounds must be absorbed. Snow does this.
or:
4. There must be amplification of the sound, by having more than one smooth
surface to bounce it back to you.

And that's what makes an echo!

Answer 7

sound waves bounce off what ever they can and come right back

Answer 8

vibrations. sound waves.

Answer 9

WHAT? What? what?