Eggs Float or Sink?
Sink or float? That’s a common question when it comes to placing objects in water. And for eggs, we expect them to sink – after all, they are denser than plain old tap water. But eggs can actually float or even be suspended in the middle of a liquid.
How is this possible? Density holds the key!
In this experiment, we’ll be exploring the effect different saltwater densities have on eggs. By layering regular tap water carefully over very dense salty water, we can create a cool density column right in a bottle! When gently placing a raw egg in this unusual water layering, its movements through the liquid showcase some neat science principles related to densities between fluids.
Let’s crack open this egg-citing science!
Materials:
- 3 transparent plastic bottles
- 3 fresh eggs
- Salt
- Water
- Scissors
- Spoon
What to do?
- Cut the top part of each bottle.
- Fill the first bottle with water.
- In the second bottle, add 3 spoonfuls of salt, top up with water and stir thoroughly until all the salt dissolves.
- In the third bottle, add 2 spoonfuls of salt and fill with water up to a little more than half the height, stir thoroughly until the salt dissolves.
- Now, slowly and using the spoon to minimize turbulence, gently pour tap water over the saltwater layer.
- Gently, place an egg in each bottle and observe what happens.
How does this happen?
In this experiment we see three containers with water. When an egg is placed in the first container it sinks, in the second it floats, and in the third it hovers in the middle. How can this be?
First let’s understand what makes objects float or sink.
For an object to float on water it needs to be less dense than the water.
The more dense a material, the heavier it is and therefore the more likely it is to sink.
An egg is denser than water and therefore sinks in it. So what is the difference between the water in the different containers?
The first container has regular water. The second container has saltwater – salt dissolved in water. When salt dissolves in water, the salt particles fit between the water particles, effectively filling the spaces between them, making the water more dense.
In this new denser state, the egg is now comparably less dense than the saltwater and therefore floats.
How then can we explain the egg suspended in mid water? Here a small trick was utilized – the container is half-filled with saltwater, and gently layered over the saltwater was regular tap water, taking care not to mix the liquids. Since regular tap water is less dense than the saltwater, it floats over it. (This is also why oil floats on water – it is less dense). When we place the egg in the water, it starts sinking through the regular tap water which is less dense than itself. When it reaches the dense saltwater layer below and floats!
If we were to mix the liquids thoroughly, we would end up with a solution of intermediate salt concentration in which the egg may either float or sink, depending on precise densities.
This experiment can also be useful to distinguish fresh eggs from older eggs. As an egg ages, water inside evaporates and air takes its place. Since air is far less dense, older eggs will float while fresh ones sink.
We’d love to showcase your creativity!
Share pictures of your experiments with us, and together, we can inspire young scientists everywhere!
