Ask one child to place 6 ounces of water in a glass cup.
Choose another child from the class and have her add 6 drops of food coloring to the glass and stir to combine. Let the children know that the food color is being used so that you can easily spot the oil.
Locate a third volunteer to pour 2 tablespoons of oil in the glass. Have the volunteer try to mix the oil in with the colored water. Allow a few minutes for observation.
Explain to the children that density is how much something weighs. When a liquid weighs less than another liquid, it floats. The heavier liquid remains at the bottom.
Ask students which liquid weighs less. They will respond with the word oil. Ask the opposite question of which liquid is heavier. The children will tell you the water is heavier.