Kinetic Terms

1. Jan 30, 2008

robousy

I've been wondering about terms you typically find in the action of a field theory, for example consider the kinetic term of a scalar field

$$S=\int d^4x(\partial_\mu\phi\partial^\mu\phi).$$

I've read that it can be thought of as the kinetic energy of the field - but this just doesn't sit to well with me for some reason. I mean the kinetic energy of a massless field seems strange.

Can anyone here provide any deeper insights into this?

2. Jan 31, 2008

mjsd

does a photon has kinetic energy?

3. Jan 31, 2008

Marco_84

mjsd is right

think the defintion (classically also) of what K is???

roughly speaking is the amount of energy that a system has, due just to his movement.

massles particles do move always at c.

4. Jan 31, 2008

robousy

hmmm... well I know that a photon has energy $$E=h\nu$$, but I've never called it knietic energy - but I see what you are getting at.

5. Feb 1, 2008

Marco_84

rember also that for m=0 E=pc