PHYSICS · Single correct · AP · Physics 1: Algebra-based · Fluids · Fluids
Problem
In a lava lamp, coloured wax blobs rise through the liquid column and then stop at a certain height before starting to sink again. Which statement best explains why a blob comes to rest at that particular height?
(a) The upward drag force on the blob exactly balances its weight while the blob’s density remains greater than that of the liquid.
(b) Atmospheric pressure becomes much lower near the top, so the blob effectively loses its weight at that height.
(c) Its density becomes equal to the density of the surrounding liquid layer at that height.
(d) Surface tension keeps pulling the blob upward until gravity suddenly takes over at that level.