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.
To je prikaz nečega što u fizici zovemo zakon očuvanja kutne količine gibanja, koji kaže da ako nešto zavrtite oko fiksne osi, nastavit će se vrtjeti tako dugo dok to ne zaustavite.