Hacker News Reader

A heavy car or SUV at 5.6mph has about the same kinetic energy as me on my bike at 28mph (25x weight difference / 5x speed difference).

I don't know about you, but I would prefer not to be hit head on by an adult on a bike traveling 28mph!

On the other hand, an actually stopped car could definitionally not hit someone.

View on HN

This is a naive analysis of the forces involved. Would you rather be hit by a semi-truck going 1mph or a bike going 28mph?

The semi truck won’t actually “hit” you. Not in a way where you’re imparted with it’s full kinetic energy.

The semi-truck will come to a stop a lot slower than a bike, and because I won't be able to avoid either I'd rather get hit by the bike.

> Would you rather be hit by a semi-truck going 1mph or a bike going 28mph?

I'm actually not sure. The initial impact would hurt more with the bike, suggesting that perhaps momentum or something else proportional to velocity (not v^2) is a good heuristic there.

But if I tripped after impact, the bike would do no further damage to me and the semi would be ~1s away from killing me.

Reply on news.ycombinator.com