Anyone who has ever tried to carry another person on their shoulders in a pool, will have made an interesting discovery. Even if somebody is normally much to heavy for us, it is easy to carry that person in the water.

What is the reason for this? Do we become stronger or does the other person have less weight under water?

The correct answer: The person is seemingly lighter because he or she is pushed upwards by the water, and the water helps to carry, so to speak!

This phenomenon is called buoyancy. Every object that is submerged in the water is affected by an upward force, which is called buoyancy. It is generated by the pressure, which exists in every fluid due to the fluid’s own weight. The pressure increases the deeper you are submerged.

The extent of this buoyancy was discovered a long time ago (around 200 BC) by the Greek physicist Archimedes:

The buoyancy is as great as the weight of the liquid that was displaced by the submerged body.

This law is also called the Archimedes’ principle. According to the legend, Archimedes discovered this fact while he was sitting in the bathtub and noticed that his body appeared lighter than when he was outside. Out of joy he is said to have exclaimed, "Eureka!" ("I found it!")

The greater the volume of the submerged body, the more water it displaces and the greater is its buoyancy as a result. The mass is not relevant in this case.

Furthermore, the buoyancy is dependent on the density of the liquid, since the greater the density, the greater the weight of the displaced fluid’s volume. You can notice the difference between the buoyancy in pure water and salt water. Salt water is slightly more dense, so the buoyancy is stronger. That is the reason why it is so difficult to submerge in the Dead Sea, which is especially salty!

You can observe the difference between salt water and freshwater in an experiment:

You need two hard-boiled eggs and two glasses filled with water. Add two teaspoons of salt to one glass and stir well. Afterwards, place an egg into each glass. The egg in one glass will float; the egg in the other will sink to the bottom. Surely you already guessed, in which liquid this would happen?!