What happens to the shower curtain when the water from the shower head starts flowing? What phenomenon or principle is this an example of?

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A helium-filled balloon is in your car which is stopped at a stop light. When you accelerate your car forward, the balloon

A. goes to the front of your car.    B. goes to the back of your car.    C. explodes.    D. contracts and falls to the floor.   

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A tall beaker is mostly filled with water and has a squeezable ball on top that can send air into the beaker. Another, inverted beaker is partially filled with water and floats in the larger beaker. When the ball is squeezed, what happens to

the water level in the tall beaker?
the water level in the small beaker?
the position of the small beaker?