Someone with a British accent constructed this device:
It's a small car with two spools for wheels. A toy wheel rests on top of the spools. Pushing the car to the right causes the spools to rotate clockwise and the big wheel to rotate "anticlockwise," as expected. He then proposes to lightly set the edge of a ruler on top of the big wheel and use it to push the top of the wheel to the right. What will the car do?
One stuffed animal says the big wheel will be turned clockwise, turning the spools anticlockwise, causing the car to move to the left. Another stuffed animal says the ruler will push the car to the right, but the wheels will push it to the left, and it just won't go. A third stuffed animal says it will go to the right, but can't say why. What do you say?