An Answermug friend told me about "the velocity of money". The speed at which money circulates. It varies from time to time, place to place. How is knowing that useful?

There is a formula in economics that is of the same form as velocity, so it is called "velocity of money". Actually, the velocity of money is constant because when you buy something the money is locked up until the end of the day, and often longer than that. But the concept of a velocity is useful to think about. In a financial panic, with inflation jumping twice a day, then the money actually moves a little faster as people try to spend it as fast as possible.