Ping Pong Attraction
		Materials: Two pingpong balls A straw Some string

Procedure: Hang the two balls near eachother but with a small gap between them. Blow air between them. Watch them come together.

Explanation: The gap between the two balls acts as a contraction, locally speeding the flow up and curving the streamlines. The local curvature causes a pressure drop, resulting in a pressure difference across each ball. This pressure difference will force the balls together. Once the balls come too close, they will get blown out by the stream as well.