WATER MAGIC - WATER EXPERIMENTS FOR KIDS

Watermagic

Experiment #10 - Making an Egg Float

The objective of this activity is to learn how salt affects the buoyancy of water.

Materials:
raw egg, hard-boiled egg, glass of water, salt, tablespoon

  1. Put the raw egg in the glass of water. Watch what happens. Take the raw egg out of the glass.
  2. Put the hard-boiled egg in the glass of water.
  3. Add salt, one tablespoon at a time, until something happens to the egg.
  4. Once you have finished with step 3, take out the hard-boiled egg and put the raw egg into the glass. What happens?

Salt makes the water heavier. As the salt water becomes heavier, the egg is able to float. The key to floating is that the object (the egg) has to weigh less than the water it displaces (takes the place of). Adding salt makes the water heavier, so eventually the egg weighs less than the salt water it displaces. The raw egg weighs less than the hard-boiled egg, so it can float in both the tap water and the salt water.

Experiment #11 - The Water Bulge

This experiment will demonstrate how water creates a "skin" that allows leaves and insects to float on it.

Materials:
plastic 8 oz. glass, 8 oz. of water, two drops of food coloring, 10 pennies or dimes, one piece of cardboard, tape

  1. Put two drops of food coloring into the water. Pour the water into the glass.
  2. Fit the cardboard around the top of the glass, forming a collar. Tape it in place. Hold the coins on the end of the cardboard and gently slip them into the water.
  3. Notice how the top of the water bulges out above the glass and toward the cardboard.
  4. Count the number of coins that you can add to the glass before the water overflows.

Water molecules are attracted to each other, creating a tight bond. This is called surface tension. Water molecules that are surrounded by other molecules are attracted in all directions. But the molecules at the surface do not have any water above them. They are strongly attracted downward to the molecules below. This prevents the molecules from spilling, even when the water level rises above the rim of the glass. Eventually, the volume of water above the rim of the glass becomes too great for the surface tension to hold, and the water spills.