# Understanding acceleration problem

1. Jul 21, 2008

### DeepSeeded

When one object accelerates away from another object, relativly they are both accelerating away from each other. The second object's speed is changing relative to the object truly changing it's speed. However the second object does not feel the "push" from the acceleration.

I am having trouble understanding why only one object is truly accelerating and feels the "push" or force of acceleration. It is intuitive that only you would feel the force as you accelerated away from someone else, however I don't understand why.

Another example is that the earth is rotating around the sun, however you could say that the sun and everything else is rotating around the earth, if you kept the earth centered. Though the sun does not feel the acceleration, the earth is truly the object changing its velocity direction and feels the acceleration force, but what determines this..?

2. Jul 21, 2008

### cesiumfrog

Re: Acceleration

That statement is false. Velocities are relative, accelerations (and angular velocities) are not relative.

Also, your mention of gravity is a bad example (since gravity is not a force, and what you probably thought of as gravitational acceleration is better conceptualised as the absence of acceleration to resist the curvature of spacetime).

3. Jul 22, 2008

### DeepSeeded

Re: Acceleration

If you watched one object accelerate away from another with no backround depending on what object you focused on either object would apear to be accelerating.

4. Jul 22, 2008

### Primordial

Re: Acceleration

DeepSeeded : The object that undergoes the acceleration relative to an independent observer if a light source exists on both the object that is accelearting and the object that is not accelerating, will allow the two objects to determine which has undergone an energy change due to the acceleration, by the independent observer.
The reason the acceleration is felt, is due to inertia. Inertia may soon be understood, if the Higgs field boson, that mediates mass is reveled in the LHC.

Last edited: Jul 22, 2008
5. Jul 22, 2008

### cesiumfrog

Re: Acceleration

That relates to Mach's principle (an unanswered and still debated question in theoretical physics), suffice here to say that in practice there is always background constellations.

6. Jul 23, 2008

### DeepSeeded

Re: Acceleration

That is a good point about the doppler shift. About only one changing in energy. If you pointed a doppler gun at both objects only one would return a shift. That helps thanks.

7. Jul 25, 2008

### therector24

Re: Acceleration

I think that it depends about your reference which shall has v = 0

8. Jul 25, 2008

### DeepSeeded

Re: Acceleration