1. The two forces that act on you when you float on your back in a swimming pool are the gravitational force and the buoyancy force.
2. Buoyancy refers to the upward force exerted by a fluid (such as water or air) on an object immersed in it. It is caused by the difference in pressure exerted by the fluid at different depths. Surface tension, on the other hand, is the cohesive force experienced at the surface of a liquid that causes it to behave like a stretched elastic sheet. While buoyancy is related to the displacement of fluid by an object, surface tension is related to the cohesion of the liquid molecules at its surface.
3. Water produces the greater buoyancy force compared to air. This is because water has a higher density than air, meaning that for a given volume of water, there is more mass present. In turn, this higher mass leads to a greater buoyant force exerted on an object immersed in water.
4. The three forces acting on a water spider when it is standing on a still pond are gravitational force, buoyancy force, and surface tension force.
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5. If the buoyancy force is the same as its weight, the object will neither sink nor rise to the surface but remain at the same position in the fluid. This is known as being neutrally buoyant.
6. If the buoyancy force is less than its weight, the object will sink in the fluid.
7. Humans cannot walk on water because the gravitational force acting on them is greater than the buoyancy force exerted by the water's upward pressure. Additionally, the surface tension of water is not strong enough to support the weight of a human walking on it.