Newtonian Mechanics – Why Does Something Round Roll Down Faster Than Something Square?

Question

Why does something round roll down faster than something square?

That's a question given to me by my five year old son.

^{So let's not get into detailed discussion about what is 'square' and what is 'round' or what is 'rolling down'.}

I thought that this might be interesting enough to ask here.

The question relates to the simple observation that 'round' objects roll down a 'hill' or 'slope' very fast.

Can we say something insightfull or intuitive about this? For instance, I can imagine that different objects might roll down faster on a straight slope, or different objects do better on a slope with bumps. What makes an object roll/fall down fast?

Answer 1

If I was answering a 5 year old, I would probably say something like this:

Because the corners get in the way, but round things don't have corners.

Also, this example comes to mind:

When you lie down on a hill and roll down, if you stick out your elbows away from your body, they will get in the way (hit the ground) and slow you down.