A block of wood floats in a glass of water. The glass is placed in a drop tower (inside a box that can be allowed to free-fall for a few seconds). When the box inside the drop tower is released, what happens to the block of wood?
A) It floats higher and stays there.
B) It floats higher for a bit and then comes back to it original location.
C) There is no change.
D) It sinks in the water and stays there
E) It sinks in the water and bounces back up to its original location.
F) Something else
G) It depends or I can't tell.
Solution: D. In the accelerating frame of reference inside the box, the gravitational/weight force becomes zero and the buoyant force becomes zero (as the weight of fluid displaced becomes zero). From the outside point of view, the buoyant force becomes zero because there are no pressure gradients in the water. So it seems at first glance that there should be no change in the position of the block (everything has zero force on it or everything is freely falling together). BUT, there is a very small downward surface tension force by the water on the wood that becomes significant when other forces are removed. This plunges the wood downward until drag force stops it. See this video.