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# Theory - To establish the relationship between Tap water & Strong salty water, Physics, Science Class 9 Notes | EduRev

## Class 9 : Theory - To establish the relationship between Tap water & Strong salty water, Physics, Science Class 9 Notes | EduRev

The document Theory - To establish the relationship between Tap water & Strong salty water, Physics, Science Class 9 Notes | EduRev is a part of the Class 9 Course Science Class 9.
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Our Objective

To establish the relationship between the loss in weight of a solid and weight of water displaced when the solid is fully immersed in the following solutions:

• Tap water

• Strong salty water

This can be done by using at least two different solids in the experiment.

The Theory

When a metallic block is immersed in water (or any other liquid), four vertical forces act upon the block below the surface of water. These forces can be grouped into two types of forces.

• Downward forces

• The weight of the block.

• The downward thrust due to pressure of the liquid on the upper surface of the block.

• Upward forces

• The tension of the spring, which measures the apparent weight.

• The upward thrust due to liquid present below the lower surface of the block.  This upward thrust is known as Buoyancy

What happens to the weight of a body when immersed in water?

The more a body is immersed in water, the more the weight of the body decreases. The weight of the body is least when it is completely immersed in water. This means that loss in weight of the body increases as it is completely immersed in water.

When a body is partly or completely immersed in water (or any other liquid), then:

Loss in weight of body = Weight of water (liquid) displaced by the body = Buoyant force or upthrust exerted by water (any liquid) on the body.

It was Archimedes who first observed that bodies lose their weight when immersed in water. He proposed a principle based on his observation that is now known as the Archimedes' Principle.

What does Archimedes' Principle state?

The Principle states that: “A body immersed in a liquid loses weight by an amount equal to the weight of the liquid displaced.”

Archimedes principle also states that: “When a body is immersed in a liquid, an upward thrust, equal to the weight of the liquid displaced, acts on it.

Thus, when a solid is fully immersed in a liquid, it loses weight which is equal to the weight of the liquid it displaces.

The more the density of liquid in which the solid is immersed, the less is the weight of the liquid displaced on immersing the solid.

Does a body float?

Some bodies, if dropped in water, sink, such as a  stone or a metallic needle. On the other hand, some bodies, even of the same weight as that of those that sink, float on water.  This can be proved through the Laws of Flotation.

What does the Law of Flotation state?

A body will float if the weight of the body is equal to the weight of the liquid displaced.
If the weight of the immersed body is more than the weight of the water displaced, the body will sink.

Learning outcomes

The results obtained confirm Archimedes' Principle. They prove that:

1. When a body is partly or completely immersed in water, it loses weight.

2. A body loses its maximum weight when it is completely immersed in water.

3. When a body is partly or completely in water then:

• Loss in weight of the body = Weight of water displaced by the body = Buoyant Force or up-thrust exerted by water on the body.

• Volume of the water displaced = Volume of the body immersed in water.

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## Science Class 9

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