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# Physics/Conservation of energy

Question
Hi Sir,

A train moving at constant speed...input work just  matches resistance and therefore no net force hence no acceleration. What about in space where there is no resistance...will the object keep on accelerating forever? Thanks

> What about in space where there is no resistance...
> will the object keep on accelerating forever?

Yep.

If you input energy into a system, and all the energy goes into the kinetic energy of the system (ie, no heat from friction), then the system's kinetic energy can only increase. In other words, its velocity will increase, thus there is an acceleration.

Relativistic effect will eventually cause the object (as viewed in the frame at which the object began at rest) to gain mass, thus the acceleration will be less and less measurable. For example, doubling the kinetic energy when the object is at 98% of the speed of light will make the object accelerate up to 99% of 'c' but not (1.96)c

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Have been fascinated by physical laws ever since I learned, at age seven, that magnets work under water. My study continued through college and has not ceased even after I retired.

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B.A. in Physics (with honors) from University of California at Berkeley.M.A. in Physics (with honors) from University of Texas Austin.