Answer: Archimedes' principle states that an object submerged in a fluid experiences a buoyant force equal to the weight of the fluid it displaces. This principle can explain why a rock sinks in a lake, but a piece of plastic with the same mass as the rock floats.
Explanation: The rock has a higher density than water, so when it is submerged in the lake, it displaces an amount of water equal to its own volume. The weight of the water it displaces is less than the weight of the rock itself, so the buoyant force acting on the rock is not enough to counteract its weight, causing it to sink.
On the other hand, the piece of plastic with the same mass as the rock has a lower density than water. When submerged, it also displaces an amount of water equal to its own volume. The weight of the water displaced is greater than the weight of the plastic, leading to a buoyant force that is greater than the weight of the plastic. This upward buoyant force keeps the plastic afloat on the surface of the water.
