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.
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.