Feynman Lectures on Physics:

Conservation of Energy

What is energy?

Imagine a child, perhaps "Dennis the Menace"

Energy is an abstract concept When all is calculated energy is

constant We see that the energy is the same

before and after but don’t understand why

What is energy?

“we have no knowledge of what energy is. We do not have a picture that energy comes in little blobs of a definite amount. It is not that way.”

There are many forms of energy and we have formulas for all of them to put in an equation

Gravitational Potential

“Let us also make a hypothesis: that there is no such thing as perpetual motion”

Can consider a weight balance machine GPE = Weight X Height

Reversible machine = XNormal machine = Y

Y is less than X otherwise perpetual motion!!

3mX=m3X

Kinetic Energy

“Of course, the fact that motion has energy has nothing to do with the fact that we are in a gravitational field. “

In the case of kinetic energy a pendulum can be considered

KE=weight X height A formula is needed that

relates velocity to height Turns out to be KE=WV2/2g

Other types of energy

“Ordinarily when things roll, there is bumping and jiggling because of the irregularities of the material ”

Consider a Spring Adding the weight X heights

doesn’t check out! Something needs to be added Spring stops moving after a time

There are many types of energy like light, heat, radiation etc.