The Digital Bits Science Labs are fun science experiments for young children. Kids, make sure you have an adult's permission before trying any of these science experiments.
Digital Bits Science Lab
Science Experiments for Kids, Parents and Teachers
Learn about buoyancy. This lab answers the question: Why is it easier to swim in the ocean than in a lake?
An egg (it can be either raw or hard-boiled. It needs to be fresh.)
A tall, wide glass
A long-handled spoon for stirring in the glass
Salt (you’ll need a lot of salt, more than what’s contained in a salt shaker. If you’re purchasing for a group or class, shop for salt in bulk.)
The Digital Bits Science Lab Experiment:
Carefully place your egg in the empty glass. Then fill the glass with water, leaving an inch or so of space at the top. You’ll see that the egg sinks, and rests happily at the bottom of the glass. (If your egg floats in the fresh water, that’s an indicator of an old egg. Use a fresh egg instead.)
Now that we’ve seen the egg sink, use the spoon to carefully lift the egg out of the glass.
Next, pour salt into the water.
And pour a little more.
The goal is to get so much salt in the water, that you can’t dissolve any more. Stir the mixture for a while. If you lift the spoon out after stirring, and still see a few salt grains clinging to it, your salt-water mixture is ready.
Using the spoon, carefully lower the egg into the water. If you’ve mixed enough salt in the water, the egg will now float!
The egg floats in the salt water because it has more buoyancy in salt water than in fresh water. Buoyancy is determined by the density of the water. Fresh water is not very dense. Things will sink easier in fresh water. Salt water consists of water mixed with a LOT of salt. That salt adds density to the water. So when you put the egg in salt water, the heavier density of the water causes the egg to float.
This is why it’s easier to swim in the ocean than in a lake: the ocean is salt water, a freshwater lake is not. Your body is more buoyant in the higher-density salt water, and you can more easily float.