Is there mass without momentum?

E is the total energy (rest energy plus kinetic energy) and p is the momentum. In summary, there is a concept called "rest mass" that refers to the mass of a body at rest. However, since rest is relative, it is impossible to accurately determine the mass of an object. Additionally, mass increases with velocity, leading to the idea that mass is simply a "shaded" version of speed in a given reference frame. Some argue that this concept can be better understood through the concept of mass-energy, where objects do not become harder to accelerate due to increased mass, but rather due to increased energy. This is calculated through the equation E^2 = (m_0 c^2)^2 + (
  • #1
azabak
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There's something called "rest mass" that is the mass of a body in "rest". But since rest is relative it is impossible to surely know something's mass. We also know that mass increses with velocity, so it seems possible that mass is nothing but a "shaded" speed in a certain referential.
Share your ideas about the subject.
 
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  • #2
In my bathroom I am at rest relative to myself and the scale. I thought there was a different way of looking at it that didn't require relative mass per se, but an understanding of mass-energy, objects don't get harder to accelerate due to increased mass if you say F = (mass-energy) * acceleration, then it is due to increased energy?
 
  • #3
azabak said:
There's something called "rest mass" that is the mass of a body in "rest". But since rest is relative it is impossible to surely know something's mass.

The name "rest mass" is a historical artifact and can be rather misleading. Physicists nowadays prefer to use the name "invariant mass." It can always be calculated from an object's momentum and energy using

[tex]E^2 = (m_0 c^2)^2 + (pc)^2[/tex]

i.e.

[tex]m_0 c^2 = \sqrt{E^2 - (pc)^2}[/tex]
 

1. Is mass an independent property or does it depend on momentum?

Mass is an independent property and is not dependent on momentum. Mass is a measure of the amount of matter in an object, while momentum is a measure of the object's motion.

2. Can an object have mass without having any momentum?

Yes, an object can have mass without having any momentum. For example, a stationary object has mass but no momentum because it is not in motion.

3. Is it possible for an object to have momentum without having any mass?

No, it is not possible for an object to have momentum without having any mass. Momentum is directly proportional to an object's mass, so an object must have mass in order to have momentum.

4. How does the relationship between mass and momentum affect an object's motion?

The relationship between mass and momentum plays a crucial role in an object's motion. A larger mass will result in a greater momentum, which means the object will be harder to accelerate or decelerate. On the other hand, a smaller mass will result in a smaller momentum, making it easier to change the object's motion.

5. Can an object have mass and momentum but not be in motion?

Yes, an object can have both mass and momentum but not be in motion. This is because an object's momentum is determined by its mass and velocity, not just its velocity alone. Therefore, an object can have a non-zero momentum even if it is not moving.

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