Rest Mass and Preferred Frame of Reference

In summary, Einstein's theory of relativity is based on the concept of relative motion and the non-existence of a universally defined state of rest. However, he also acknowledges the existence of rest mass. Observers may not agree on whether an object is at its rest mass, as it depends on their relative motion. This means that every object, regardless of its speed, can be considered to be at its rest mass by an observer moving at the same speed. This does not contradict the concept of mass-energy equivalence, as this relationship is primarily based on an object's rest energy. Additionally, the force of gravitational attraction between an object and observers in different inertial reference frames is not dependent on the object's speed, as determined by the relativity
  • #1
nsh3a94
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Einstein's theory of relativity is based on the fact that all motion is relative, which precludes the existence of a universally defined state of rest (priviledged reference frame). Einstein also recognises the existence of rest mass. If an object were at its rest mass, wouldn't it be perfectly stationary; in a universally defined state of rest?
 
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  • #2
nsh3a94 said:
If an object were at its rest mass, wouldn't it be perfectly stationary; in a universally defined state of rest?

Observers don't agree on whether an object is at its rest mass.
 
  • #3
Every object, at any speed, is "at its rest mass" to an observer moving at the same speed.
 
  • #4
bcrowell said:
Observers don't agree on whether an object is at its rest mass.

Wouldn't all inertial reference frames that are observing the force of gravitational attraction between themselves and an object accelerating in a direction opposite to its absolute velocity vector will register a minimum force of attraction at the same time, which would signal the object having reached its rest mass?
 
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  • #5
HallsofIvy said:
Every object, at any speed, is "at its rest mass" to an observer moving at the same speed.
Wouldn't this explanation deny the mass energy equivalence?
 
  • #6
nsh3a94 said:
Wouldn't this explanation deny the mass energy equivalence?

Certainly not. That "the mass of a body is a measure of its energy-content" relates first of all to the rest energy, see:

- http://www.fourmilab.ch/etexts/einstein/E_mc2/www/

Note about gravitational attraction: Everything was derived on the basis of the relativity principle, according to which no "absolute velocity vector" can be detected. The force of attraction is therefore not a function of speed in the way you perhaps think.

Harald
 

What is rest mass?

Rest mass is the measure of an object's mass when it is not moving. It is also known as invariant mass or proper mass. It is the same for all observers regardless of their frame of reference.

What is the preferred frame of reference?

The preferred frame of reference is the one in which the laws of physics are simplest. It is the frame of reference in which the laws of physics appear to be the same for all observers.

How does rest mass relate to energy?

According to Einstein's famous equation, E=mc², rest mass is a form of energy. This means that mass and energy are interchangeable, and an object's rest mass contributes to its total energy.

Does an object's rest mass change with its velocity?

No, an object's rest mass remains constant regardless of its velocity. However, its relativistic mass, which includes the effects of its velocity, will change.

What is the significance of rest mass in special relativity?

Rest mass is a fundamental concept in special relativity, as it is a property of an object that remains constant in all inertial reference frames. It helps to explain the equivalence of mass and energy and has important implications for the laws of physics and the behavior of objects at high speeds.

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