The Properties of Hydrostatics

1903 Words Feb 20th, 2014 8 Pages
Three containers are filled with water to the same height and have the same surface area at the base: hence the water pressure and total force on the base of each is the same. Yet the total weight of the water is different for each. Explain this "hydrostatic paradox"
The key to this problem is that the force on a container due to the hydrostatic pressure is always perpendicular to the surface of the water. According to Newton’s 3rd law, the container will push back on the water in the exact opposite direction, also perpendicular to the surface of the container
Consider what happens when you push both a pin and the blunt end of a pen against your skin with the same force. Decide what determines whether your skin is cut. The net force
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Will an empty balloon have precisely the same apparent weight on a scale as a balloon filled with air? Explain.
If air is incompressible, then yes.The full balloon will have more weight (more downward force), due to the mass of the air in the balloon. The full balloon will also have an upward buoyant force on it, equal to the weight of the air displaced by the balloon. Since the balloon is both containing air and floating in air, the weight of the air inside the balloon is the same magnitude as the buoyant force. Filled balloon has a higher apparent density compared to empty balloon.
IF you dangle 2 pieces of paper vertically a few inches apart and blow between then, how do you think the papers will move?
The papers will move toward each other. Bernoulli’s principle says that as the speed of the gas flow increases, the pressure decreases (when there is no appreciable change in height). So as the air passes between the papers, the air pressure between the papers is lowered. The air pressure on the outside of the papers is then greater than that between the papers, and so the papers are pushed together.
Children are told to avoid standing too close to a rapidly moving train because they might get sucked in under it. Is this possible? Explain.
It is possible. Due to viscosity, some of the air near the train will be pulled along at a speed approximately that of the train. By Bernoulli’s principle, that air will be at a lower pressure than air further
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