# Generalised energy and energy (lagrangian mechanics)

1. Jan 12, 2012

### supaman5

I'm doing lagrangian mechanics and trying to understand my notes, are these three statements correct:

1. If kinetic energy is quadratic then energy equals generalised energy.
2. Saying kinetic energy of a system is quadratic is the same as saying none of the position vectors in a system depend explicitly on time.
3. A lagrangian can be independent of time (generalised energy is conserved) even if kinetic energy is not quadratic (energy DOESN'T equal generalised energy)

2. Jan 13, 2012

### supaman5

Hopefully putting the formulas for generalised energy and energy might help:

L=T-V (kin-pot)

generalised energy: h= $\sum\frac{\partial L}{\partial \dot{q}}$$\dot{q}$-L where $\dot{q}$ should be bold and is the time derivative vector for all generalised coordinates.

and energy: E=T+V

Took me about an hour to write out that formula...FAIL.