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.
Beakman explains density by weighing out different volumes of different items. He then shows how a balloon filled with helium is less dense than one filled with our own air so therefore it rises.
Hank explains why solid water is less dense than liquid water even though solids are typically more dense than liquids. He also discusses how the high heat capacity of water helps support life on Earth. He uses the bodily process of sweating to exemplify water's unique properties.