# Special theory of relativity

Hello all,

I just need some help understanding inertial frame of reference, is this when there is no acceleration acting on a body. such as, gravity.. but the body can be under constant velocity or at rest. Also, Could someone please help me with this senario: there is a guy in a rocket, bill, he takes off a constant velocity and then there is a girl, ellen, whom is watching the rocket. To bill, ellens watch seems to be going slow, but to ellen bills watch seems to being slow. what is the cause of this?

Thanks alot.

An inertial reference frame is a frame which is not accelerating and where all the laws of physics hold. I think you are misunderstanding frames vs. objects. A frame can track an object, but it isn't the object. If you are on a train, then a frame is the coordinate system that moves with the train, not the train itself.

What you are talking about is the twin paradox. The fact that you said Bill "takes off" means he accelerated to his velocity from Ellen's frame. This is general relativity, but the jist of it is that Bill's clock is running slower than Ellen's.

Hello all,

I just need some help understanding inertial frame of reference, is this when there is no acceleration acting on a body. such as, gravity.. but the body can be under constant velocity or at rest. Also, Could someone please help me with this senario: there is a guy in a rocket, bill, he takes off a constant velocity and then there is a girl, ellen, whom is watching the rocket. To bill, ellens watch seems to be going slow, but to ellen bills watch seems to being slow. what is the cause of this?

Thanks alot.

It takes time for light to travel from ellen to bill, or from bill to ellen