Push an empty can in water. You will feel an upward force and you will find it difficult to push the can further. Water exerts force on the can in the upward direction. When a body is immersed in a liquid, the liquid exerts an upward force on the body. This force is called the upthrust or buoyant force.
Why do you feel lighter when you are in a swimming pool? This is due to upthrust. The effect of upthrust is that weight of the body immersed in a liquid appears to be less than its actual weight. There are two factors on which upthrust depends - Volume of the body and Density of the Liquid. Larger the volume of body submerged in liquid, greater is the upthrust. More the density of liquid, greater is the upthrust.
Upthrust = Volume of body x density of liquid x acceleration due to gravity.
Learn why bodies with density greater than density of liquid sink while body with density less than density of liquid float.
You can find out the magnitude of the upthrust by Archimedes' Principle. Archimedes' Principle states that when a body is immersed partially or completely in a liquid, it experiences an upthrust, which is equal to the weight of the liquid displaced by it. This principle is applied to liquids as well as gases.
Upthrust in Fluids and Archimedes Principle
Learnhive Lesson on Upthrust n Fluids and Archimedes Principle
Archimedes' tale takes place some 2,200 years ago when King Hieron II of Syracuse in Sicily gave a jeweller a bar of gold and ordered him to make it into a crown. The king, however, suspected that the jeweller had substituted some of the gold for cheaper metal like silver, while pocketing the leftover gold. The king had no way of proving his suspicions, so he asked Archimedes – a Greek mathematician, engineer, inventor, and astronomer – to find a definitive answer. Archimedes had spent a long time trying to figure out the answer, which came to him when he noticed how water would splash out of his bath tub the moment he stepped into it, and the more he stepped into the tub, even more water got displaced. At the time, Archimedes had known that gold was denser than silver, so if a certain weight of silver had been substituted for the same weight of gold, the crown would occupy a larger space than an identical one of pure gold. So to find the crown’s volume, all Archimedes had to do was essentially immerse the crown and exact measurement of pure gold in a tub filled with water to the brim, measure the spillage, and compare the volume of spillages – if the jeweller had indeed made a crown of pure gold the volume should be the same. Archimedes was said to be so thrilled with this discovery that he immediately hopped out of the bath and ran onto the streets naked shouting 'Eureka!' 'Eureka!'.