During the Apollo 15 space mission, astronaut David Scott decides to test Galilleo's theory that all objects fall at the same rate, despite their weight, in the absence of an atmosphere. In his test, he drops two objects with drastically different weights, a hammer and a feather, at the same time.
Beakman demonstrates that marshmallows are less dense than the same amount of water and therefore, marshmallows float. Nails are heavier than the same amount of water so they sink. He then explains water displacement by getting into a tank of water. His DIY demo for this is making a aluminium boat that floats in a bowl of water but when you crush the aluminum foil into a square, it sinks because it couldnt' displace the water.
In an attempt to collect the Golden Idol, Indiana takes the idol and replaces it with a bag of sand the same size. That doesn't work, as the traps still activate, and Jones needs to escape quickly or meet his fate.