# Soup Can Race: Help

1. Dec 12, 2007

### sugarfreeky22

Soup Can Race: Help!!!

Later this week my high school physics class is having the traditional soup can race. However, we have four cans to work with:1 stock can that must be the fastest, one stock can that must be the slowest, 1 modified can that must be the fastest, and one modified slower can. If I am not mistaken, the larger but lighter cans, with less dense fluids, should be the fastest, correct? I am in desperate need of suggestions for the modified cans version. The cans can be modified in that materials may be added to them, so long as no sort of motors are attached. :)

2. Dec 13, 2007

### Astronuc

Staff Emeritus
For a can to be fastest, it needs a greater mass and minimal diameter. The moment of inertia, which provides resistance to rotation, increases linearly with mass, but quadratically with radius.

http://hyperphysics.phy-astr.gsu.edu/hbase/icyl.html#icyl2

Larger cans with less mass will rotate more slowly than smaller cans. Larger cans will also have more air resistance.

To get more mass in a given volume, one must fill the volume with denser material.

3. Dec 13, 2007

### FredGarvin

Astro takes all the fun out of Pinewood Derby car races too...:tongue2:

4. Dec 13, 2007

### J77

How about sloshing effects if the cans aren't full...

5. Dec 13, 2007

### belliott4488

Well, let's not forget the advantage that liquid-filled cans have over, say, a can of baked beans. Since the liquid will not rotate initially, the only moment of inertia to consider is that of the empty can. Ideally, a very heavy but very non-viscous fluid would be best, I'd think.

6. Dec 13, 2007

### Danger

What in bloody hell is a 'soup can race'?