Question

A solid cube of ice floats in water. Which is more dense: ice or water?

Short answer

Water is denser than ice.

Step-by-step solution

Understanding the Problem

To determine whether ice or water is more dense, we need to consider how density affects floating. A substance will float if it is less dense than the medium it is in.

Density Formula

The density of a substance is calculated using the formula \( \text{density} = \frac{\text{mass}}{\text{volume}} \). To compare ice and water, we don't need exact values but rather need to understand their relative densities.

Ice Floats on Water

Since the cube of ice is floating, it implies that the ice is less dense than the water. If the ice were denser, it would sink instead of floating.

Conclusion

Because the ice cube floats, this indicates that the density of ice is less than the density of water. A substance that is less dense than the surrounding fluid will float.

Key concepts

Floating

Floating occurs when an object is buoyant in a fluid, such as water. For an object to float, its density must be less than the density of the fluid it is placed in.

• If the object's density is less than that of the fluid, it will rise to the surface and float.
• However, if its density is greater, the object will sink.

This principle is governed by Archimedes' principle, which states that a body submerged in a fluid experiences a buoyant force equal to the weight of the fluid displaced by the body. In simpler terms, when an object is submerged, the pressure from the fluid below pushes it upwards, helping it to float. The ability to float is crucial in understanding the behavior of objects in liquids and gases. In this exercise, the floating of ice in water is a clear indication that the ice cube is less dense than the water surrounding it.

Ice

Ice is the solid form of water and forms when water is frozen below 0°C (32°F).
The molecular structure of ice is such that it forms an open hexagonal lattice. This structure contributes to ice being less dense than liquid water.
Unlike most substances, water expands when it freezes. This is because the molecules arrange themselves in a way that occupies more space, resulting in ice having a lower density.

• This structural anomaly makes ice float on water.
• The lattice structure of ice is crucial to understanding many natural phenomena, such as the floating of icebergs and the ability of ponds to freeze over without harming aquatic life below.

The presence of air trapped in ice also contributes to its buoyancy. The combination of its crystalline structure and trapped air makes ice less dense, leading to its typical behavior of floating on water.

Water

Water is a versatile liquid known for its unique properties. It has a maximum density at about 4°C.
This unique property arises because water molecules are packed more closely together at this temperature.
When water is warmer or cooler than this temperature, the molecules are less tightly packed, resulting in a slight decrease in density.
The density of liquid water allows it to support objects that are less dense, such as ice, making it possible for ice to float.

• Water's density decreases when it freezes, allowing ice to float, equilibrating ecosystems.
• This property is vital for many environmental systems, such as ensuring that aquatic habitats can survive the winter under a protective layer of ice.

Understanding water's density and its phases is essential in fields ranging from environmental science to engineering, impacting everything from climate studies to the design of ships and submarines.