# Homework Help: How a cube(a die) bounces

1. Aug 19, 2007

### Mins

How a cube(a die) rolls(rolling motion help)

I want to show how a cube bounces and rolls when dropped from a slope(45 degrees).
I'm trying to make this problem as easy as possible, so I've ruled out air current.
How will it bounce? Think I need to use 'e'(elasticity)(which is roughly 0.3)...
Then, I don't understand why it rolls when it's airborne... Does it roll at all? Did I miss something?

Another thing that bothers me is it's rolling motion when it's not bouncing up and down... (Not sure of it and dunno what determines rolling friction)
Where does the axis of the die lie?
and what is conserved, and what isn't???

extra)http://director-online.com/buildArticle.php?id=1075#dice

Last edited: Aug 19, 2007
2. Aug 19, 2007

### Astronuc

Staff Emeritus
Die are three dimensional objects. The interaction with a surface is asymmetric (striking a surface on one corner, edge or face), and the force acting in opposition to forward motion acts at a distance to its center of mass, which produces a 'moment' about the center of mass, and hence the development of rotational motion.

The collision is largely elastic since there is little deformation of the surface or die.

3. Aug 19, 2007

### Mins

I think I understand but

4. Aug 19, 2007

### Mins

...

or suggest a formula to calculate?