What If the Moon Crashed Into Earth? (You’d Get 5 Days)

Thought experiment: the Moon stops going around Earth and drops straight down. It would take about 4.8 days to arrive.

The math in this video: free-fall time from Kepler’s third law (4.8 days), tidal pull scales with 1 over distance cubed (about 9x at halfway), the fluid Roche limit near 18,400 km, and an impact energy of about 3.5e30 joules against roughly 3.5e27 joules to boil every ocean. Real ocean tides respond in a more complicated way, so the nine times is about the pull, not the wave height. The Mars-sized impact is the giant-impact hypothesis (NASA, Space.com).

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