Every physics class is hit, at one point or another, with the famous Monkey and a Gun problem. The idea is simple: A biologist has decided to shoot a monkey — let's say with a tranquilizer dart, The monkey is hanging on a vine when the biologist spots it. By reflex, it will release the vine the moment it hears the bang from the gun, and the biologist knows this. Where should the biologist aim?

Some people will say the biologist should aim below the monkey. Some say it depends on the speed of the projectile. Those who have heard the demonstration before will say the biologist should aim right at the monkey. Gravity will pull the monkey and the dart down the same distance in the same amount of time. The speed of the dart doesn't matter. If it's fast, it will only drop a little as it flies, but because it gets to the monkey so quickly, the monkey will only drop a little, too. If the dart is slow, the monkey may be nearly all the way to the ground before the dart gets close, but the dart will also have dropped nearly all the way to the ground, and will still hit the monkey.

But why take my word for it. Check out MIT students, a golf ball gun, and a stuffed monkey.