It's a demonstration of something in physics that we call the law of conservation of angular momentum, which basically says that if you set something spinning about a fixed axis, that it will keep spinning unless you do something to stop it.
물리학적으로 설명하자면 각운동량의 법칙이라고 일컫는데요. 고정축을 두고 물리적으로 회전을 주면 멈추게 하지 않는다면 계속 회전합니다.