Why does a cone-shaped object, when placed on its side on a flat surface, rotate about the end with a smaller diameter?

Question

Examples include a light bulb, a screw, a nail, etc.

I intuitively know how these objects behave, but I’m having trouble putting it into words/reasoning about it.

Is it because of the tilt? The diameter difference (this causes the tilt)?

In: 9

Answer 1

First, let’s start with a cylinder. When a cylinder rolls 360 degrees, it will travel the same distance as it’s circumference (if the cylinder was 1m around, then when it rolled 360 degrees it would travel exactly 1m). It travels in a straight line because both ends of the cylinder have the same circumference, meaning both ends travel the same distance when they rotate.

If we change the circumference of one of the ends of a cylinder to make it smaller, then for every 1 rotation of the object, one side will be traveling a lot less than the other causing it to spin. This is similar to how if one person in a canoe isn’t rowing as fast as the other, the canoe spins.