The nozzle makes the water flow through the upper part of the table tennis ball. If the angle and velocity of the water jet are well controlled, the table tennis ball will rise to the sky. The string is used to hold the table tennis ball and prevent it from being washed away by water. Someone told me that it's because of Bernoulli's law, because the water above table tennis is is moving, and the air below table tennis is is static. But I don't believe that explanation. Because of the relativity of movement, I can also say that the air under table tennis is is moving, while the water is static.
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It is the combination of two effects: Newton's $\dot{m_1}\overrightarrow{v_1}= \dot{m_2}\overrightarrow{v_2}$ , conservation of momentum. And Bernoulli's law.
The water stream washing off the top of the table tennis ball gets narrower around the ball and also deflects down.
By Bernoulli law the presser is reduced in the back of the ball because water moves faster. And by deflecting down because of viscosity, we have a $\dot{m} \overrightarrow{v} $ change downward, which creates equal and opposite and upward momentum in the ball. Similar to an airfoil.
kamran
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