# Does energy causes motion?

1. May 26, 2013

### gamow99

Some guy is trying to tell me that energy does not cause motion, motion is just a brute fact.

Here is a quote from Hodgson:

I think that rather solidly equates motion with energy. Energy is typically described as the ability to do work.

W = Fd or W = (MA)d

In order to achieve distance you need motion.

Further in the equation, KE = .5mv^2 kinetic energy is equated with velocity. If there is no velocity, then there is no motion. And if there is velocity then there is no Kinetic Energy.

Finally, mass is equated with energy. There is a lot of energy just in one's hand but we can't get to it. Well, if we could get to it, we could get a lot of work done, that is to say, we could move mass some distance, again, motion.

2. May 26, 2013

### Crazymechanic

Well technically speaking yes , energy in many cases comes in the form of kinetic energy , in macro scale objects like planets and cars and others, or in atoms and elementary particles.
Like the temperature of a gas is the relationship to it's particles average kinetic energy , the lower the temperature the lower the energy.

you said that if there is velocity there is no kinetic energy , I believe this was just a "typo" but it is wrong , velocity of a particle or an object is it's kinetic energy which you could measure if the object or particle would crash into something like a detector.
It goes vice versa like judging the cars speed after looking at the collision damage and so.

Well mass is potential energy, it's stored in a certain state in which it is unusable for doing work but once released it can do work while it looses it's potential energy and then you have to give it back again like taking the rock and putting it up on the tree again for it to fall down and hit a target or something like that.
the spring analogy works well here as you can push a spring and then release it later while it is compressed it has a added potential energy just like a rock sitting on a tree above ground.

3. May 26, 2013

### mikeph

I don't understand the quote. What two things does classical physics distinguish between, kinetic energy and...?

4. May 26, 2013

### krash661

unit of work.
simple.

5. May 26, 2013

### joebro8659

There are many different guises of energy. I think the one that's confusing you is potential energy:
The conventional definition of potential energy is the stuff that is build-ed up, and required for motion. The more energy you have, the more motion can occur, and the more easily motion can be achieved. Think of it this way. If I drink a gallon of 5 hour energy (and I don't die) I have so much potential energy than little movements happen so easily, it's as if it is out of my control. So I shiver a bit. However, though it requires effort not to shiver because it is easier to make little movement than to not because the abundance of potential energy that I have gives it that ease. So Motion Requires potential energy, and potential Energy makes simple motion easy, I can still stop myself. Again potential energy doesn't cause motion, just makes it easier.
Kinetic Energy is the other way around. It is created by moving things. Potential energy usually leads to kinetic energy because of the ease given to move is from the potential, and movement creates kinetic. Skydivers can almost feel the transformation of potential to kinetic energy. But again ease isn't the same as forcing something to happen.

Last edited: May 26, 2013