If i use a certain amount of energy/work - lets say 0,36 J - to wind

1. Feb 29, 2012

johann1301

If i use a certain amount of energy/work - lets say 0,36 J - to wind up an old alarm clock, will the mass of the clock increase, or will the clock just get hotter somehow?

2. Feb 29, 2012

zhermes

Re: E=mc2

Good question. In general, it depends on the particulars of the situation. In the case of an alarm clock, there is generally a system of springs which stores the energy and potential energy---which would increase the effective mass of the system. At the same time, energy is always lost to heat (especially the bearing, and the spring's metal).

3. Feb 29, 2012

johann1301

Re: E=mc2

I would think that the mass in the spring would get hotter and denser, but not bigger? Would it really weigh more than before?

4. Feb 29, 2012

zhermes

Re: E=mc2

It doesn't get any 'bigger' in size; but yes, the mass of the system would increase. This is a measurable effect in atomic nuclei where the total mass is larger for a bound system than for the constituent parts alone (same idea of potential energy being stored in the system).

5. Feb 29, 2012

Drakkith

Staff Emeritus
Re: E=mc2

Mass is a property of matter, it cannot get hotter and denser itself. If you increase the mass of something it will weigh more than it did before.

6. Feb 29, 2012

Dreamer350

Re: E=mc2

Can somebody explain this please- I'm now a little confused.

7. Feb 29, 2012

Drakkith

Staff Emeritus
Re: E=mc2