Action definition

1. Jan 24, 2009

o_neg

Hi,

why is the action defined as the integral of the Lagrangian over time?
i don't see the meaning of integral on the (kinetic - potential) energy

thanks,
ori.

2. Jan 24, 2009

clem

The integral has no meaning by itself, but setting its variation equal to zero leads to the equations of motion.

3. Jan 24, 2009

phreak

You can see the integral as a way of measuring how much of something is used. So in this case, the integral measures how much (K-U) energy is being used up, and the path that a particle takes minimizes this (this isn't technically correct... it takes a 'stationary' path, but looking at it this way could be beneficial to the student visually).

4. Jan 25, 2009

o_neg

thanks for the replay.

I found a detailed explanation in the Feynman lectures on physics vol 2