[ChrisH]

Of course if you are crushing cans without mechanical aid, you want to use the following method. I practiced it far too many times after I learned it in college (but only on soda cans).

1) Empty the can

2) Place the can on a reasonably level piece of ground.

3) Stand on one foot on top of the can.

4) While balancing on top of the can, reach down and tap both sides of the can simultaneously.

Standing on the can places it under a fairly uniform compression load. Tapping the can causes the side to deflect in, the deflection causes stresses to rise leading to a buckling failure of the can.

The resulting squashed can is nice and compact. Some cautions, wear shoes that will allow air to escape as the can crushes and be sure that can is empty.