newton's first law is true. If there were 0 gravity, the hamster would simply rotate all over the hamster wheel. But since there's gravity, when the hamster moves forward, the gravity pushes it back down, making the wheel rotate.
I bet he's thinking about other women; According to Newtons first law, 'An object at rest remains at rest, or if in motion, remains in motion at a constant velocity unless acted on by a net external force', so how do hamster balls move if the hamster is on the inside