# Does Gravity Cause Waves?

by Sammy101
Tags: gravity, waves
 P: 39 When you move your hand with a slinky in it, the slinky begins to move because you gave energy from your hand to the slinky. A wave is not always formed, but when the disturbance from your hand is rhythmic, a wave will form. Is this right so far? A force acted on the slinky and caused a disturbance. Gravity is a force that acts on all objects with mass including air molecules. Therefore why does gravity not create a disturbance on air molecules and cause sound or movement as in a wave?
 P: 11 Yeah, gravitational fields do create gravitational waves. They're just not very detectible since gravitational forces are so weak compared to anything else; especially if you're comparing the gravitational force of a binary star system hundreds of light years away to the electrostatic interactions between two molecules. It is possible to detect gravitational waves though; http://en.wikipedia.org/wiki/LIGO
 P: 39 Hey thanks for the response! Im really interested in what you are saying but I think what I am trying to get at is that if a force as small as that coming from my hand can move a spring then can a force like gravity (which I know is not very strong though) cause wave motion between air molecules in Earths atmosphere for example?
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## Does Gravity Cause Waves?

Well the problem is that the force due to gravity on the air molecules is constant, while the force that you're applying to the slinky is changing. To have a wave you need a restoring force and some other force. For example, a bouncy ball will create a "wave" of sorts.

But in the case of air molecules just chillin' in the atmosphere, there's nothing to really make them "wave" at all.
 P: 39 Thanks! That helps a lot to understand that you need a restoring force to create waves because I was always kinda confused on how waves were actually formed beyond just giving a medium energy or a disturbance. Is this restoring force of gravity in water waves or tension and gravity in guitar strings what causes waves to oscillate in curves which can be represented by a sinusoidal function?
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P: 10,391
 Quote by Sammy101 Thanks! That helps a lot to understand that you need a restoring force to create waves because I was always kinda confused on how waves were actually formed beyond just giving a medium energy or a disturbance. Is this restoring force of gravity in water waves or tension and gravity in guitar strings what causes waves to oscillate in curves which can be represented by a sinusoidal function?
Exactly.
 P: 39 okay this is all making sense but when I send a single wave pulse (such as a crest) through a rope for example, why does gravity as a restoring force not push this pulse down to the equilibrium position to the trough and then pull it back up to form a crest? When we did experiments with a rope or slinky in physics and sent a single pulse, the pulse would remain a crest (or trough) the entire lenght of the rope. Why does gravity not act as a restoring force here?

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