Did you know that the Red Sea is the saltiest body of water in the world? If you swim in it, you will float right on top! This activity will help make more sense of this phenomenon by exploring the principles of density and buoyancy!
Understanding Buoyancy and Density
Before we start our experiment, here are some terms that are helpful to understand.
What is Buoyancy?
Buoyancy is the upward force that a fluid has on an object. Buoyancy works opposite to the force of gravity and is the reason why objects are able to float!
What is Density?
Density is a measure of mass per unit volume. The equation for density is D = m/V, where D represents density, m is mass, and V is volume.
Materials
- 2 clear glasses
- 2 eggs
- Salt
- Spoon
How to Make Floating Eggs
Step 1
Fill each glass about halfway with water.
Step 2
In one of the glasses, pour in 10 teaspoons of salt and give it a good stir. The water should become cloudy.
Step 3
Make a prediction! What do you think will happen when you place an egg in the glass with plain water?
Go ahead and carefully put one egg in the glass without salt.
STEM Q For You! What happened to the egg? … The egg sunk to the bottom!
Step 4
Make a prediction! What do you think will happen when you place the egg in the glass with salty water?
Step 5
Repeat step 3, but this time, put the egg in the glass with salt.
STEM Q For You! What happened to the egg this time? Was it the same or different from the glass of water without salt? … The egg floats on top!
Try this! Try pushing the floating egg in the salt water down. What happens?
The egg still floats!
What influence does the salt have on the water in this experiment?
Adding salt to water increases the water’s density since salt adds mass to the water without changing the volume. Due to the increase in density salt water is able to support heavier objects.
Why Do Objects Float in Salt Water?
An object will float in a fluid when it is less dense than the fluid it is in. If the object is more dense than the fluid it is in, then it will sink.
The egg sinks in the plain water since the egg is more dense than water.
The egg floats in the salty water because the salty water becomes more dense than the egg.
