# Homework Help: Kinetic energy

1. Jan 1, 2010

### ZoeGab

I feel that I don't comprehend kinetic energy fully. I am trying to figure out under what conditions would kinetic energy not be conserved using prinicples of physics. Can anyone help me understand this better. Please try and put it in laymans terms because this is all new to me. It will not be helpful if I can't understand what you are explaining to me. I really appreciate any help anyone can provide!!!!

2. Jan 2, 2010

### rock.freak667

When you have friction, kinetic energy is not conserved. Some colliding objects don't conserve kinetic energy.

3. Jan 2, 2010

### cepheid

Staff Emeritus
Also, have another look at the work-energy theorem. It states that the work done will be equal to the change in kinetic energy. If work is done...kinetic energy will change.

4. Jan 4, 2010

### ZoeGab

How does this sound? I am not sure if this is correct

kinetic energy can be changed to electrical energy using a generator,
into heat energy using friction or inelastic collisions
into electromagnetic radiation by striking certain crystals,
into potential energy by lifting an object or compressing a gas.

5. Jan 5, 2010

### rock.freak667

Well these are true, not sure about the electromagnetic one though since I have not studied much about that.

6. Jan 5, 2010

### sigmavirus

KE changes when an external force or torque is applied to a system. W=$$\Delta$$KE=Fd for linear motion or =$$\tau$$$$\theta$$ for rotational.

7. Jan 5, 2010

### ZoeGab

Could you explain this a little further?

8. Jan 5, 2010

### sigmavirus

when a force acts on a system, KE is gained or lost (within the system at least, because energy is never destroyed). like friction. energy is lost in the forms of heat, sound, etc. and transferred to the surroundings. If you push an object from rest, exerting a force, it will gain velocity and, thus, KE. Torque is the same concept, but for rotational motion. I don't know how much you know about that, though.