uncertainty principle

The uncertainty principle is a rule made by a famous scientist named Werner Heisenberg. It says that it is impossible to know exactly both where something is and how fast it is moving at the same time. This is because if you measure where something is, it affects how fast it is moving, and if you measure how fast it is moving, it affects where it is. So if you know one of these things exactly, the other one has to be a little bit uncertain.