The Moon is slowly siphoning off the Earth’s rotational energy, in a phenomenon called tidal acceleration. This moves the Moon’s orbit farther from the Earth. According to Kepler’s laws of planetary motion, the Moon must orbit more slowly as it gets farther away. Well, which is it? Is the Moon speeding up, or slowing down?…… Continue reading Simple orbital mechanics
Planet FrictionlessIceball has a straight, narrow tunnel connecting two points on its surface. How long does it take to slide through the tunnel? Simplifying assumptions As with most story problems, we have to make some simplifying assumptions. But I think they’re fairly reasonable. We assume the faller starts out motionless, at one end of the…… Continue reading How long does it take to fall through a ball of ice?