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Did a Rock Hit Your Windshield, or Did Your Windshield Hit a Rock?

Either way, it sucks. But at least there’s some fun physics to ponder while you’re sitting in the repair shop.

We’ll start with a basic scenario, where someone ahead of you drops an object in the road, and then see what we need to make it work. The only change is in its vertical velocity: The gravitational force causes it to move down until it hits the ground, at which point, it rebounds upwards. Second—and this can seem weird—because a rock is irregularly shaped, it's possible that it spins and hits the pavement in a way that makes it skip up higher than it started.

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