Can you make the tennis ball reach the ceiling?
Using the cord, pull the bowling ball up and let it drop. Observe the tennis ball in the other tube.
As the bowling ball begins to fall, the air below it is forced out through the holes in the larger tube. Once it’s beyond the holes, the bowling ball pushes the air below it towards the smaller tube, thereby blasting the tennis ball in the smaller tube towards the ceiling.
Without the holes in the large tube, the bowling ball would fall very slowly and the tennis ball would not rise particularly high. The slow fall is the result of the fact that the ball in the narrow tube combined with the air itself are very efficient in resisting the fall of the bowling ball. When the air is able to escape through the holes in the larger tube, no such air column resisting the fall of the bowling ball is created. The ball manages to achieve such a great speed so that it easily pushes the air in front of it, thereby sending the air with force into the smaller tube and launching the tennis ball to great heights. The rapidly falling bowling ball produces a much greater thrust than a slowly falling bowling ball. The speed of the tennis ball is further increased by the fact that the speed of the propulsive air increases as it is forced from a larger tube into one with a smaller diameter.
Some bicycle pumps have a small hole at the upper end of the cylinder. The point of the hole is to facilitate the initial speed of the piston, thereby easing the work of the person pumping the air.
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