For instance if someone is hit by a train or a car, why does it kill them? How does the impact kill them.
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We think of our bodies as single objects that generally stay the same shape (not counting motion of our joints), but we’re really squishy bags of skin and bones with organs loosely anchored inside.
When you’re hit by something large, fast, and solid, the part of your body it touches first basically immediately has to accelerate up to the speed of the thing. That means a very large acceleration, which means a very large force. That can crush/break things because they get squashed before they can move out of the way.
As the motion continues, the now fast-moving parts of your body run into the parts that haven’t started moving yet…like your organs. And bendy things like bones are bending as one end moves but the other end hasn’t got up to speed yet. Organs get whacked and can burst, bones break, blood vessels stretch and break.
Once your whole body is up to speed the immediate acceleration damage stops but all the initial damage is still there, and it starts causing other problems. Broken bones stay broken, and those jagged ends can poke/stab adjacent things…more organ & blood vessel damage. All the holes poked in your circulatory system lead to blood loss and shock. If lungs are punctured by rib bits, you can’t breath. Leaking blood can put pressure on your brain. Things that should have stayed inside their respective tubes (food, blood, feces, urine) may leak out into places they shouldn’t be and are now poisoning the things around them.
Edit:typo
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