Question

There is some water in the beaker placed on the pan of a spring balance. If we dip our finger in the water without touching the bottom of the beaker, then what is the change in the reading of spring balance?

Answer 1

Hint: We are asked to state the change in the reading of the spring balance. We can answer this question based on the concept of Archimedes’ principle and Newton's third law of motion. We can start by stating Archimedes' principle and Newton's third law of motion. Once we have stated both the principles


Complete step by step solution:
We can answer this question by stating and explaining the concepts one by one. The two concepts involved in this solution are Archimedes' principle and Newton’s third law of motion. Let us state the same one by one.
Archimedes’ principle states that any body that is partially or fully immersed in a fluid experiences an upward force also known as buoyant force which is equivalent to the weight of the fluid displaced by the body.
Newton's third law of motion states that for every action, there is an equal and opposite reaction.
According to Archimedes' principle when the finger is dipped in water, it experiences an upward buoyant force. Now Newton's third law comes into play. When the upward force is present, there comes an equal and opposite force and this causes the reading to increase.
In conclusion, the reading on the spring balance increases.

Note:
The Archimedes’ principle has many applications. Some of its applications are lactometers which are used to check the purity of a certain amount of milk and the most easily observable application is the building of ships and submarines. Hydrometer is another important application which helps in estimating the density of a fluid sample.