When the cylinder is spinning clockwise, friction between the cylinder walls and the air causes the speed of the air in front of the cart to become greater than the speed of the air in back of the cart.  According to Bernoulli's Principle, the faster moving air in front of the cart exerts less pressure on the cylinder than the slower moving air in back of the cart.  This difference in pressure causes a net force which causes the cart to move forward along the track.

1. Wind the string onto the Bernoulli cart pulley.
2. Place the cart on the track and pull the string.
3. With the cylinder spinning and the cart stationary on the track, turn on the fan and point it at the cart from the side.
4. The cart will accelerate down the track as long as the spinning cylinder is in the fan air flow.