# About reference frames

1. Aug 27, 2004

### tardon007

hi folks!!

I have a question which had been haunting me for quite some time.....

can an observer sitting in a accelarating reference frame deduce that he is accelarating with out establishing any contact with the outside world( i am alluding to outside the frame ambience)?

2. Aug 27, 2004

### PRodQuanta

Please be more specific of what you are asking. Are you saying that a person is moving through space, but he has no other landmarks to see that he is moving?

Paden Roder

3. Aug 28, 2004

### Clausius2

I think surely he can.

In fact, this was discussed in the General Relativity theory. One can distinguish between inertial and non inertial reference frames, by means of experimental effects. One of them is the property of weighting bodies to remain in their original status. If you are pushed or accelerated forward, your body will tend to remain at rest. In particular, your body or any weighting body will experiment a reaction rearward -m*a.

Imagine you are travelling by train, without windows. You could hang your umbrella on some cross bar. Then you will see the umbrella turning a little angle rearward while the train is accelerating. This effect is enough clear to state you are really accelerating forward.

On the same way, you can state the Earth is turning around Sun and not the contrary, by means of the centrifugal force.

In non-inertial reference frames there are certain forces that are present only at this type of frames.

4. Aug 28, 2004

### arildno

A typical 2-D "accelerometer" consists of 4 springs of equal, unstretched length the one ends of which are attached to the middle point of the sides of a square "box", whereas their other ends are attached to a ball (or something) sitting in the middle of the square box.
If the box is stationary with respect to a noninertial frame, the ball will no longer remain in the middle of box.

5. Aug 28, 2004

### chronon

Part of the foundation of general relativity is the idea that an observer sitting in a accelerating reference frame can deduce that he is not in an inertial frame but cannot distinguish between the effects of acceleration and that of an external gravitational field.

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