Buoyancy is the force that causes some objects to float in water but allows other objects to sink. The density of the water and the size of the object combine to determine whether an object will float or sink. Gravity pulls down on all objects. Water pushes back against objects. An object that weighs less than the amount of water it displaces will float. The more water an object displaces the greater the buoyancy or upward push of the water. This is why a large, heavy ship will float, but a pebble will sink. Some objects that sink in fresh water will float in denser salt water because the amount of salt water displaced weighs more than the same amount of displaced fresh water. Buoyancy can be demonstrated using an egg, some water and table salt. An egg will sink to the bottom of a glass of fresh water, but will float in salt water. (See reference 2)
Things You'll Need
Labels
Black marker
1 raw egg
Tap Water
Salt
2 glass containers
Spoon
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Instructions
1
Write the words "fresh water" on one label. Write the words "salt water" on another label. Place a label on each glass container. Fill both glass containers 1/2 full with regular tap water.
2
Pour 10 tablespoons of table salt into the glass container labeled "salt water." Stir the water using a spoon until the salt is dissolved. Place the egg in the glass container labeled "fresh water." Observe the egg sink to the bottom of the container.
3
Salt water is denser than fresh water.
Remove the egg from the fresh-water container using the spoon. Place the egg in the salt-water container. Observe the egg float near the top of the salt water. Remove the egg from the container.
4
Pour the fresh water slowly into the salt water solution. Pour the water down the side of the salt water container by tilting the glass slightly. Place the egg carefully in the water solution. Observe the egg sink until it reaches the denser salt water.