Final answer:
Objects that are less dense than water float, while objects that are denser than water sink. Temperature can also affect whether a substance floats or sinks in water. Ice floats in water because it is less dense than liquid water.
Step-by-step explanation:
Objects that are less dense than water float, while objects that are denser than water sink. For example, oil is less dense than water and floats on it, while metals are denser than water and sink. The density of a substance determines whether it will float or sink in water. If a substance's relative density is less than one, it is less dense than water and will float on it. If the relative density is greater than one, the substance is denser than water and will sink.
Temperature can also affect whether a substance floats or sinks in water. Most materials expand as temperature increases, which usually decreases their density. In the case of water, its density decreases as it gets warmer. This is why ice floats in water, even though it is a solid and usually solids sink in liquids. Ice has a lower density than liquid water because the water molecules are spaced farther apart in ice, due to the hydrogen bonding between them. This expansion of water molecules in ice makes it less dense than liquid water, allowing it to float.