Why Doesn't Gravity Act as a Restoring Force in Wave Pulses?

[Sammy101]

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?

 

[qalomel]

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

 

[Sammy101]

Hey thanks for the response! I am 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?

 

[SHISHKABOB]

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.

 

[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?

 

[Drakkith]

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.

 

[Sammy101]

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 length of the rope. Why does gravity not act as a restoring force here?