E=MC^2 Question

[deadcat]

Does this mean if I had a rubber band and weighed it, then stretched and weighed it while being stretched out, that it would weigh more at that time? Since at that time it has stored energy, which equates to mass?

 

[Nugatory]

Yes, that is what it means. And a charged battery will weigh slightly more than discharged battery, and so forth.

It is a worthwhile exercise to calculate just how much mass increase we're talking about... Try it!

 

[TheDemx27]

Yes, that is what it means.

If you stretch out a rubber band the energy is converted into elastic potential energy. The fact that the rubber band is stretched out proves that the vast majority of the energy cannot go anywhere else, eg. mass.