Suspended Egg

Will the egg sink or float? Try this activity and ‘eggsperience’ the suspense!

Australian Curriculum links

  • Science > Chemical Sciences > Year 4 > ACSSU074

You'll need

  • glass jar or tall drinking glass
  • water
  • raw egg
  • teaspoon
  • salt

Try this

  1. Half fill the glass jar with water.
  2. Use the teaspoon to gently lower the egg into the water.
  3. Observe whether the egg floats or sinks.
  4. Use the teaspoon to remove the egg from the water.
  5. Add 3 teaspoons of salt to the water, stirring thoroughly until the water becomes less cloudy.
  6. Use the teaspoon to gently lower the egg into the salty water and the egg should now float. If the egg doesn't float, remove the egg, add more salt to the water and try floating the egg again.
  7. Now the egg is floating, very carefully add fresh water to the glass by pouring water over the back of the teaspoon and down the side of the glass. Don’t allow the fresh water and salt water to mix.

Further investigation

Test which other liquids float on water (eg. fizzy drink, vinegar, vegetable oil, milk, baby oil etc).

What's happening?

The egg sinks in fresh water because the egg has a higher density than the water. Salt water has a higher density than fresh water. The egg floats in the salt water because it is less dense than the salt water.

Density is a measure of how much mass is in a given volume. Density affects buoyancy. Buoyancy is the upward force a fluid exerts on an object that is less dense than the fluid. An object will sink if its weight is more than the buoyant force, and an object will float if its weight is less than the buoyant force.

The egg has a higher density than the fresh water and the egg’s weight is greater than the buoyant force. Therefore the egg sinks in the fresh water. When salt is added to the water, it increases the density of the water. If enough salt is added, the egg becomes less dense than the salt water and its weight becomes less than the buoyant force. Therefore the egg floats in salt water.

Because fresh water is less dense than salt water, the fresh water floats on top of the salt water. The egg floats between the fresh water and the salt water because the egg’s density is between the densities of fresh water and salt water.

Real world links

Dissolved salts make up 4-6% of water in the ocean. Because ocean water has a higher density than fresh water, it is easier for humans to float in the ocean. The Dead Sea however, contains approximately 25-30% salts by weight/mass. Therefore, humans can float with ease on the surface of the Dead Sea without any effort at all!