# Physical Explanation of a Pull-Back Car

1. Jan 9, 2005

### deanchhsw

Hello. I have troubles understanding how the pull-back car works in a physical sense, so I decided to post a question.

By "pull-back" car, I mean one of thoese Hess Cars where you pull and the spring inside it shrinks and once you release the car the spring inside gives it a thrust forward.

However, I need to come up with the physics-related concepts on how it works. I have considered recoil velocity, but if I remember correctly
recoil velocity is related to Newton's third law, like how the gun gets a backward movement after it fires the bullet, proportional to its mass, so I don't think it has anything to do with the Kinetic Energy generated by the spring. So, what is going on? Obviously, as a student I have yet to learn all the concepts in Physics, so please tell me,

how can you explain(or calculate) the energy generated by the shrunken spring when it is released? not in common sense, but in phyiscal sense.

THANKS!!

2. Jan 9, 2005

### dextercioby

The answer to your last question is elementary.Just apply the law of conservation for total energy...So it involves KE and elestic nature potential energy.

Daniel.

3. Jan 9, 2005

### deanchhsw

Oh. I never knew that there was an "elastic nature" for the potential energy.

That's what I needed, thank you so much :)

4. Jan 9, 2005

### dextercioby

If u don't like that word,maybe:"elastic origin,elastic kind" would do... :tongue2:

Daniel.

PS.You're welcome.