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

Options

A. Sea water is still while river water is running
B. Saltnity of sea water is more than that of river water
C. Density of sea water is more than that of river
D. none of the above

Explanation

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks why swimming is easier in the sea compared to a river. To answer this, we need to consider the properties of the water in both environments.

2. **Density of Water**: The density of seawater is greater than that of river water. This is primarily due to the presence of dissolved salts and minerals in seawater, which increase its overall density.

3. **Buoyant Force**: The buoyant force is the upward force exerted by a fluid on an object submerged in it. It is directly related to the density of the fluid. The greater the density of the fluid, the greater the buoyant force acting on an object.

4. **Effect of Density on Swimming**: When swimming, a person’s body experiences buoyant force. In seawater, because of its higher density, the buoyant force is greater. This means that a swimmer will feel lighter and will require less effort to stay afloat.

5. **Comparison with River Water**: In contrast, river water has a lower density. Therefore, the buoyant force acting on a swimmer in a river is less than that in the sea. This results in a greater effort required to stay afloat and swim effectively.

6. **Conclusion**: Since the buoyant force is greater in seawater due to its higher density, it is easier to swim in the sea than in a river.

### Final Answer:
It is easier to swim in the sea than in a river because the density of seawater is greater than that of river water, resulting in a higher buoyant force that helps swimmers stay afloat with less effort.

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