How Does the Temperature of Water Affect Its Density?

Directions: (print this page):

This activity explores how the temperature of water affects its density. You will need to gather the following materials: a pencil; a small paper cup; a small-mouthed, clear-glass jar (the cup should be able to sit inside the opening of the jar); three ice cubes; and food coloring.

1. With the pencil, poke holes in the side of the cup, near the bottom.
2. Fill the jar with warm water and set the cup inside the mouth of the jar.
3. Predict what will happen when you add cold, colored water to the cup. Draw your predictions.
4. Place the ice cubes in the cup and leave them to melt for two minutes. Then, place several drops of food coloring in the water in the cup.
5. Observe what happens as the colored water in the cup goes through the holes and into the warmer water in the jar. Which seems more dense, the cooler, colored water or the warm water? How can you tell? Draw your observations.

(From Science & Children, March 1996)