physics question #2036



Michel Lamontagne, a 47 year old male from Edmonton asks on April 5, 2004,

Q:

Why does sound get through a surface like a wall better than light? If you use a curtain they both get through. If you use a drywall/2 by 4 wall the light won't make it through but the sound will. If you use a massive wall like a foundation some of the sound will likely get through, but none of the light. If you shine a light and play a ghettoblaster at a sand dune the sound will go around (like wrap around) the dune but the light will either not make it over the crest of the hill or just shoot over the top without "wrapping" around the hill. How does this all work? Sound is vibration, ok and light is what, particles?

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the answer

Barry Shell answered on April 8, 2004, A:

While sound and light can both be thought of as waves, they are different kinds of waves. Sound is a pressure wave and the pressure needs to have some stuff to press. Sound can only happen in a medium. In other words it needs atoms to transmit itself. It needs air or water atoms that can be compressed in a regular way so that when they hit your eardrums these atoms push on your ear drums to make them vibrate at a frequency. In other words, things, stuff, matter, moves to make sound. With light the waves are electromagnetic. They are not made of stuff. They are made of energy. Light can go through a vacuum. It does not need any stuff to get from point a to point b. That's why we can see starlight through the vacuum of space. Sound cannot travel through a vacuum at all.

Conversely, electromagnetic waves (of visible light energies) cannot go through stuff at all. Light does not even penetrate water very far--so beyond a few hundred feet it's very dark under the ocean.

Because sound is created by atoms pushing against each other, it can push itself around things. Light and other forms of electromagnetic radiation goes in straight lines and does not "push" on a medium to make it's way around so it cannot go around things.

Electromagnetic radiation is thought to be a duality of both wave and particle, but it is neither. You have to think of it as pure energy. We use notions of waves and particles so we can wrap our human minds around the idea of a pure beam of radiant energy like light. Scientists use this wave/particle model to apply math and science to electromagnetic waves in order to figure out how light and other forms of electromagnetic radiation work. So far it has served us pretty well. There are areas where it does not work however, like with gravity, which is something else entirely.

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