Conservation of Energy

abstract idea: There is a certain quantity of energy (which can be calculated/computed) that does not change in the manifold changes which nature undergoes.

block analogy:

• energy “chunks”, they can be hidden in different places (forms), but when you count all places correctly, the total stays the same
• there are different forms (gravitational, kinetic, heat, elastic, electrical, chemical, radiant, nuclear, mass) of energy and each has a formula.

Thus energy is a number you compute from the state of a system. It’s not a material substance; it’s a conserved quantity that makes the bookkeeping of nature come out right.

Equations:
gravitational potential energy: $E_p=mgh$
change in energy: $\Delta$ = (force) x (distance force acts thru)
kinetic energy: $E_k=\frac{W{V}^2}{2g}=\frac{m{v}^2}{2}$

Concepts: conservation laws

• three subtle, involving space and time but not depend on absolute time and space:

1. conservation of energy
2. conservation of linear momentum
3. conservation of angular momentum

• three in the sense of counting blocks:

1. conservation of charge
2. conservation of baryons
3. conservation of leptons