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oasisaimlessly | on: I don't understand quantum physics (2018)
Agree, but kinetic energy being mv^2/2 rather than mv can be pretty intuitive in the right context:

> Would you father get hit with:

> * a 1 kg object moving at 1 m/s or

> * a 1 g object moving at 1 km/s?

hansvm | parent | next
I think that context obscures the kinetic energy thing though. The 1g object is more dangerous because it's able to actually pierce you. I wouldn't particularly want to be hit with a 1 mg object at 1 km/s either, especially near any major arteries, despite it having the same kinetic energy as a 1 kg object at 1 m/s, which I wouldn't care about at all.

And to illustrate the point a bit further, that same argument doesn't work in other speed/mass regimes. Would you rather get hit with:

- A 1000 kg object moving at 1 mm/s or

- A 1 kg object moving at 1 m/s

It's suddenly no longer intuitively obvious because both are totally fine. Like...roll a die, and my squishy human body will be equally happy with either result. Or, shifting the argument the other direction, would you rather get hit with:

- A 1000 kg object moving at 1 km/s or

- A 1 kg object moving at 1000 km/s

Pretty obviously the 1 kg object, despite its much higher kinetic energy. If I'm lucky it just takes off an arm or something, whereas the 1000 kg object is definitely splattering me.

And that sort of thing is why kinetic energy can be hard to reason about. Our intuition is calibrated around our squishiness, which only loosely relates to energy. There are other factors at play.

pwdisswordfishq | root | parent
> The 1g object is more dangerous because it's able to actually pierce you.

Why?

loading story #50235171
skeptic_ai | parent | next
I guess first. But 2nd seems like speed of bullet. But of first object is metal I’m fucked. If second is a feather of 1g I think won’t hurt me. So depends what it is too
hansvm | root | parent | next
500J is a lot of energy. Ballpark estimate, the feather would hurt quite a bit too. It'd have a similar impact to a 1kg steel ball at 31.6m/s (assuming it's 1000x less dense than steel) in terms of energy dissipated per unit area of skin, which is something like the mass of 7 baseballs at the speed of a typical baseball in the major leagues. I'd expect significant blunt-force trauma from a broadside feather at that speed. I'd expect much more severe injuries if it struck with a different cross-section.
adwn | root | parent
> But of first object is metal I’m fucked.

1 m/s is just 3.6 km/h, or slow walking speed. You'll be fine.