Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: [Phys-l] Relativity Question



On May 6, 2007, at 3:28 PM, David Abineri wrote:

I am looking for a high school level explanation for the following question.

Does a compressed spring have more mass than a relaxed spring (at its
natural length) by virtue of it's having more energy while compressed?

Or, perhaps more generally, how does potential energy figure in to a
relativistic point of view.

I know this is a little vague but perhaps someone who understands my
question might attempt a response appropriate to a high school level class.

1) Yes, but this is not measurable. For example, suppose a force F=100 N is used to compress the spring by d=0.1 m. The work done on the spring is 10 J. That is by how much its potential energy is increased. Divide this by c^2 to see that the mass increases by about 10^-19 kg.

2) Why do you have to explain this? Probably because you are probably dealing with relativity. In that case you already introduced the E=m*c^2 formula, probably giving some experimental evidence of its validity. That is probably enough for high school.
_______________________________________________________
Ludwik Kowalski, a retired physicist
5 Horizon Road, apt. 2702, Fort Lee, NJ, 07024, USA
Also an amateur journalist at http://csam.montclair.edu/~kowalski/cf/