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Things move from high to low pressure areas. The lower the pressure, the stronger the action. Think of a tornado - they have very low pressure in the middle of their funnel!
The mathematician Bernoulli found that moving air has less pressure than air that is still.
The curved surface of the ball made the air travel faster below the ball than the still air above the ball. The moving air below the ball had less pressure, which sucked the ball into the funnel. The same idea can be applied to vortex smoke rings too!
Bernoulli's work on the pressure of fluids and gases helped to design wings on planes.
Find out why here!