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What is sound?

A sound is actually a pressure wave created by a vibrating object. In other words, you could say that when something vibrates, it creates sound. Originating from a source, these sound waves travel outwards in all directions at the same rate. As the waves travel, they bounce off and/or are absorbed by objects that lie in their path. These waves are then picked up by our ears, which send the waves to the brain, where they are processed so we can make some ‘sense’ out of them.

Now, unlike light (which is an electromagnetic wave), sound is a mechanical wave, meaning that it needs a medium in order to travel. It cannot move through a vacuum (whereas light can). That’s the reason why space is silent, because sound cannot travel with an absence of any air.

Sound waves need to travel through a medium such as solids, liquids and gases. The sound waves move through each of these mediums by vibrating the molecules in the matter. The molecules in solids are packed very tightly. Liquids are not packed as tightly. And gases are very loosely packed. This enables sound to travel much faster through a solid than a gas. Sound travels about four times faster and farther in water than it does in air. This is why whales can communicate over huge distances in the oceans. Sound waves travel about thirteen times faster in wood than air. They also travel faster on hotter days as the molecules bump into each other more often than when it is cold.

Let's take a look at an example. Imagine a church bell. When a bell rings, it vibrates, which means the bell itself flexes inward and outward very rapidly. As the bell moves outward, it pushes against particles of air. Those air particles then push against other adjacent air particles, and so on. As the bell flexes inward, it pulls against the adjacent air particles, and they, in turn, pull against other air particles. This push and pull pattern is a sound wave. The vibrating bell is the original disturbance, and the air particles are the medium.


No, you cannot hear any sounds in near-empty regions of space. Sound travels through the vibration of atoms and molecules in a medium (such as air or water). In space, where there is no air, sound has no way to travel.

The space is almost a vacuum, as all the matters in the universe are separated by a very huge distance. So the distribution of air molecules is of insignificant amount–the density is negligible. When your friend calls you out in the space (hypothetically assuming that you are superheroes who can survive vacuum), there won’t be any air molecules to help traverse her voice–the vibration–to reach your ears. This is the reason why you can’t hear sound in space.

What's Going On?:

Unlike light, sound requires a medium to travel through. This simply means that in order to hear sound there has to be something for sound to travel through. Sound travels by vibrating the particles in the medium so that they bump into each other. As the vibrations of the particles reach your ear, your ear drum receives the vibrations which the brain then interprets as sound.

In the vacuum of space, there are no (or very, very few) particles to vibrate, so sound cannot travel through this medium. You might think this presents a communications conundrum for NASA: How can we talk to astronauts who are orbiting earth? The solution is radio waves. Radio waves travel perfectly fine through a vacuum because they are a type of electromagnetic wave (light), and electromagnetic waves do not need a medium to travel through. Similarly, we can still see light emitted from the sun even though a vacuum stands between the sun and earth.

Syringe forms vacuum inside the bottle. Because of this vacuum, you can no longer hear the bell jingle until you allow air to enter the bottle.

We know sound always needs a medium to travel through. As well as gases, sounds travel through liquids and solids. In space, there are no molecules in the large empty areas between stars and planets. We say space is a vacuum.

Space is a vacuum.

With no molecules in the vacuum of space there is no medium for the sound waves to travel through.

So there is no sound.

And that is the reason nobody can hear you shout in space. Sound cannot travel in the vacuum of space.

TEST YOUR SOUND IQ 1. Can sound travel under water? 2. Does sound travel faster through water or through the air? 3. Does sound travel faster through wood or through the air? 4. Is there sound on the moon? 5. What is the speed of sound? Answers: 1. Yes, sound can travel under the water. 2. It moves four times faster through water than through air. 3. It moves about thirteen times faster in wood than air. 4. No, there is no sound in space. Sound needs something to travel through; matter, air, liquid, solid wood. 5. Sound travels through air at 1,120 feet (340 meters) per second. 5



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