Density refers to the amount of stuff there is in a given space. Different things have different densities. For example, a cup of water has more stuff in it than a cup of oil. The water is denser. A marble and a ball of the exact same size are made of different amounts of stuff – they have different densities. Do you think the less dense oil will sink in or float on the denser water? Which is denser, the marble or the ball? How can you tell?
How do liquids of various densities interact with each other?
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