Question

Give reasons as to why it is easier to swim in sea water than in river water.
A) The density of river water is greater
B) The density of seawater is greater
C) Both their densities are the same
D) None of these

Answer 1

Hint: Seawater is salty as it contains salt that increases the density of the sea water. According to Archimedes’ principle when a body is partially or fully immersed in a fluid it experiences an upward force known as buoyant force equal to the weight of the liquid displaced by it. As a result, the weight of the liquid displaced depends on the volume and density of the liquid displaced. Use this principle to answer the given problem.

Complete step-by-step solution:Archimedes’ principle states that when a body is partially or fully immersed in a fluid, it experiences an upward buoyant force which is equal to the weight of liquid displaced by it. The buoyant force offered by seawater to a body is also more than the river water. Now, weight of the fluid displaced by the body will be directly proportional to the density of the fluid and its volume.
Since seawater has salt in it, the density of seawater is more than the river water. Note that the river water is considered as fresh water.

Note:Another factor that comes into play when swimming is the viscosity of the fluid. The viscosity of the fluid offers resistance to the relative motion between the layers of the fluid. Based on Archimedes' principle, one may think that hypothetically it would be very easy to swim in honey since it has a higher density than water and would provide more buoyant force but in reality, honey is very viscous, so it would be very hard to swim in honey.