Thread: Momentum and mass

I have just been thinking....

Lets take an object in space and start accelerating it, as we accelerate it the object takes on mass. Now, lets stop accelerating it, it keeps on going until another force acts upon it. I have the idea that as soon as an object has stopped accelerating and is not interacting with anything else, its mass returns to rest mass, regardless of its now (constant) momentum or speed.

I have come to this conclusion because, if we take an object and want to measure its mesurment or momentum, we need a frame or points of reference in order to complete this task...Lets say we take this same object and accelerate it, during its initial acceleration period, it acquires energy and mass, granted. Now when the object is travelling at a certain speed; take everything else that exists in the universe and make it disappear. Can we now measure the speed or momentum of the object ? No ! Can we say in with certainty that the object is still moving. By frames of reference, no we cannot, by the initial conditions set up at the beginning of the experiment, yes we can. Why does the object keep travelling in that same direction and at the same speed ?

Becasue there are no longer any forces acting up on it. It is balanced and stable. It has returned to its rest mass; regardless of momentum.

There's rest mass and there's relativistic mass, Leo. If you search the internet you'll find there's been a lot of debate about what mass is. The current prevailing view is that rest mass is the better definition, but I prefer relativistic mass because it offers a link between energy and mass. See MASS EXPLAINED for details. The trick is to make your massless travelling "particle" travel in a loop so it isn't going anywhere. Then the momentum is now inertia, and relativistic mass is now rest mass.

leo that is just alot of mike-stuff

it will allways have its relativistic mass relative to any referens frame of motion its not depened upon if any force is acting on it, but relative to itself it will allways ahve restmass

Originally Posted by Zelos

leo that is just alot of mike-stuff

it will allways have its relativistic mass relative to any referens frame of motion its not depened upon if any force is acting on it, but relative to itself it will allways ahve restmass

Relative to any reference frame. Thats what you just said and that is my point. Take away all all of the other matter in the universe and you no longer have any frames of reference.

And....im not saying it has no rest mass; of course it does, what im suggesting is that it ONLY has rest mass, regardless of momentum.

Originally Posted by leohopkins

Originally Posted by Zelos

leo that is just alot of mike-stuff

it will allways have its relativistic mass relative to any referens frame of motion its not depened upon if any force is acting on it, but relative to itself it will allways ahve restmass

Relative to any reference frame. Thats what you just said and that is my point. Take away all all of the other matter in the universe and you no longer have any frames of reference.

And....im not saying it has no rest mass; of course it does, what im suggesting is that it ONLY has rest mass, regardless of momentum.

Im at a loss here - how does taking all the matter out of the universe get rid off the uncountably infinite number of inertial reference frames out there?

Where would your points of reference be ? If nothing else existed ?

Um - a frame of reference is a mathematical construct, it does not depend on anything else "existing" as the point of reference is you.

I think you are missing my point a little.

um no - i think you are trying to describe a universal rest frame, which is impossible in SR.