# There is a thing called energy?

1. Feb 4, 2004

### kishtik

$$v_f^2-v_0^2=2ax$$
Multiplying by m,
$$\frac{mv_f^2-mv_i^2}{2}=max$$
$$\frac{1}{2}mv_f^2-\frac{1}{2}mv_i^2=Fx$$
This equation is true for all of the motions which include a force. Therefore we call the left side KE difference, and the right side work done.
Is energy a thing which can only be defined mathematically? Or are there any other ways to define it? If yes, why did Euler call it vis viva? Was it only because of KE? If no, what leads us to conclude that there is a thing called energy?
For almost every physical definition, we have an imagination, a perception, a conception, something inexplicable. Where is this coming from? When we were babies, playing with Legos (K'Nex for me) we learn about dynamics and perhaps energy. I've read that smells, tastes and views were perceived the same by a little baby. Perhaps we develop that conciousness at that age.

2. Feb 4, 2004

### turin

This only works if a, m, and F are constant, in general. Otherwise, you have to integrate.

3. Feb 4, 2004

### Arcon

Re: Energy

For the most part that is true. Recall what Feynman said on this point