# Why do waves(in general) travel in different frequencies?

1. Jun 19, 2010

### mapa

Why does a wave go up and down? What forces cause waves to go up and down? In order for a particle to be a specific frequency would depend on what?

2. Jun 19, 2010

### Staff: Mentor

Forces push it up and down. Consider a spring-mass system. You start it by pushing it down and then releasing it. Then the spring provides the force to keep it oscillating.
A particle isn't a wave, so the question makes no sense. What determines the frequency of a wave is the strength of the spring (the restoring force) and the magnitude of the mass (resistance to the restoring force).

3. Jun 19, 2010

### Dav333

But what about a photon moving up & down? Is there a force pushing it up/down? Wouldn't the force run out after billions of light years travel? (sounds silly due to my lack of knowledge)

Do you mean the particle is not a wave because its got the wave/particles duality & sometimes acts more like particle than a wave & vice verse?

thanks

4. Jun 19, 2010

### mapa

RUSS WATTERS

In a vacuum --such as space-- light travels in waves, but what is it bouncing off of?

Do the waves itself, naturally bounce off each other?

5. Jun 21, 2010

### Staff: Mentor

mapa, I sent you a PM - and Dav333, I know there is now another thread on the subject, so this may be redundant, but:

Light is not a mechanical wave. It is a completely different phenomena, so all this analogy to mechanical waves is just that: analogy and nothing more. Light doesn't behave exactly like a mechanical wave because it isn't one.

6. Jun 23, 2010

### seto6

because their speed has to be C so they have to change frequency and wave length

7. Sep 23, 2010

### jeebs

Not a silly thing to ask i don't think. when you think of a photon, don't think of a particle moving along on a sinusoidal or corkscrew path. either picture a point particle moving along a straight path, or a transverse wave propagating in a given direction, depending on what is most convenient to describe/understand how it behaves.
it isn't a particle that oscillates, the oscillations are that of alternately fluctuating electric and magnetic fields. there isn't really a "force" making the fields rise and fall in strength - not directly anyway. as i understand it, an electromagnetic (ie. light) wave can be generated by an oscillating charge - that WOULD require the electromagnetic force to act on the charge.

8. Sep 25, 2010

### mikeph

The wave equation permits solutions of ANY frequency, and in most cases this equation is derived from theoretically analysing whatever is moving (piece of string, pendulum, even light using Maxwell's equations).

Because the wave equation is homogeneous and linear, if you can find a set of solutions then any linear combination of those solutions is also a solution. The most general solution is the sum of all waves of different frequency. Everything you hear can be broken down into waves of different frequencies at different amplitudes. Same with everything you see, and in a sense everything you feel,taste, and smell since it's all travelling through your nervous system to reach your brain.

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