Two Mexicans
What's that? It's a Mexican spinning another Mexican around in a circle while standing on ice. I used something similar in class today (minus the hats), to demonstrate where the reaction to the centripetal force is when a body is moving in a circle on the end of a string. It's one of those questions I always like to ask the class because I know that someone is going to get it wrong and say, that according to Newton's 3rd Law there must be a force acting outwards. Well it worked today and I got the required response, this led me to show that the force is acting on the person holding the rope. If it wasn't for the friction on the ground the person on the other end would move as well. he dancing hats also demonstrates the principle of conservation of momentum. At time t=0 the blue hat is the only one moving with a velocity towards the right. The hats are isolated so momentum must be conserved, this means that when the blue one is stationary the red one must be travelling to the right, at any moment of time, t (tea time) the momentum is the same as it was at the start.