Demo2) If you hit the stick sharply, you can prevent air flowing under the paper. If there is no air beneath it , then there is no pressure to counteract the pressure from above the paper. All the air that extends up to the top of the atmosphere is pressing down on the paper. The average atmospheric pressure is 1.01×105(Pa). So the force(=weight of air) on the paper is about 18000N.
Q5) An air-filled balloon sinks because the balloon compresses the air making the density of air inside the balloon slightly greater than the air outside. Hence, the weight of the air-filled balloon is greater than the buoyant force due to the air.A helium-filled balloon floats because helium gas is less dense than air. So the weight of the helium-filled balloon is less than the buoyant force due to the air
Q6) Roofs are usually constructed to withstand downward loads(like snow), but not for increased upward loads.When a strong wind blows on the roof, the air pressure decreases, resulting in lower pressure compared to inside the house.
When you spin a ball, the ball ‘drags’ the surrounding air on its surface, creating a thin layer of spinning air. • On the top, the streamlines and the spinning air is in same direction resulting in fast move air(lower pressure) • While on the bottom, the streamlines and the spinning air cancels out. • The lower pressure on the bottom causes the ball to be pushed towards the bottom as it moves