Quick question - special relativity?

Question

Does the mass of an object in its inertial frame increase with velocity as well as the observed mass, or is it just the observed mass that increases?

In other words, does an object feel heavier when it increases its velocity.

Answer 1

Yes, it actually does increase, because the object's energy increases, and so does its relativistic mass as a result. That's why we can create super-heavy particles in accelerators when we collide lighter particles at relativistic speeds. If only the observed mass increased, not the actual mass, then this would be a violation of conservation of mass-energy.

Answer 2

No it does not. There is no absolute frame of rest against which other frames are measured. There is no absolute velocity. There is no experiment--- none--- that can be performed inside a spacecraft that can return its velocity. Therefore the object's mass is always measured to be the same in its rest frame.

Frankly, it's the same in ALL reference frames. "Mass" in physics always refers to the rest mass of the body. Physicists discarded the concept of "Relativistic Mass" long ago, for very good reasons. For other reasons incomprehensible to me, it is still taught to high school students, so that I must un-teach it in my university classes. It is very irritating.

Answer 3

Mathematically yes. As an object is travelling faster and faster, it will take constantly more force to keep it going faster still. It may take many pages to explain this concept, but the way I can maybe simplify this is that for an object to reach the speed of light, it will have to convert its entire mass into energy to get to that speed. Thus E=mc2.