Why do flies explode on impact with my windshield on the outside of the car but are able to fly around inside my car while it’s in motion without exploding all over the inside of my rear window?
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Relative velocity.
If the fly is doing 5mph and you hit it at 50mph, that’s somewhere between a 45mph and a 55mph relative velocity (depending on which way you were both travelling).
If the fly is inside the car, it’s already doing 50mph relative to the Earth, the same as the car, but it’s only going 5mph relative to the car itself.
You’re currently travelling over 1000mph. Earth is rotating you at that speed. You don’t know and don’t splat into things because everything else you see is also doing 1000mph in the same direction. So, relatively, you are doing the same speed.
You’re also travelling around the sun, the sun is travelling around the galaxy, the galaxy is spinning at ridiculous speeds.
None of it matters if you’re ALL moving at the same speed. The only thing that matters is the *difference* in speed between you and the thing you hit.
It’s why hitting a stationary car at 40mph is exactly the same as hitting a 30mph car at 70mph. The physics are basically identical. What matters is the relative velocity, not the actual velocity (because, for a start, you have no idea what velocity you’re doing right now – because of all those other things that are also moving you, that I mentioned above).
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