Question

Why is it easier to swim in sea water than in river water?

Answer 1

Hint: In this question use the concept that when a body floats in water it comes across two basic forces that is the gravitational force and the buoyant force. The net force acting upon a body is the difference of the buoyant force and the gravitational force. So the smaller this difference is, the easier it will be for the body to float. Think whether the buoyant force is higher in sea water or in river water. This will help approaching the problem.

Complete step-by-step answer:
As we all know that the quantity of salt present in the sea water is very high as compared to the river water.
Due to high salt in the sea water the density of the sea water is higher as compared to river water.
So as the density increases the buoyant force also increases.
When something is floating in the water they feel two forces on the body which is floating.
$\left( i \right)$ Gravitational force
Due to gravity the substance goes down and the body does not float.
$\left( {ii} \right)$ Buoyant Force
The volume of the water displaced by the body is determined by the buoyant force.
How much buoyant force the less the displaced water and the body gets easily floated.
The body has to weigh less than or equal to the displaced water in order to float or swim.
So buoyant force is a very necessary force for swimming.
So the resultant force acting on the body in upward direction is the subtraction of the buoyant force and the gravitational force.
So how much buoyant force the body will swim easily.
So the buoyant force is higher in the sea water as compared to river water.
So it is easier to swim in the sea water as compared to the river water.
So this is the required answer.

Note – Another great reason behind the easier floating in the sea water as compared to the river water is because the net weight of the body floating in case of any water body is real weight – Buoyant force. As the buoyant force is more in the sea as compared to the river the net weight of a body is less and thus it is easier to float.