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# Gravitation

## 11 Principle of Floatation

#### WHY OBJECTS FLOAT OR SINK IN A LIQUID?

Two forces act upon, when an object is put in a liquid.

• Weight put of the object acting downwards which tends to pull down the object and
• Buoyant force (or upthrust) acting upwards which tends to push up the object

Three cases arise when an object is dropped in a liquid:

• Object sinks in the liquid, if the buoyant force (or upthrust) exerted by the liquid is less than the weight of the object.
• Object floats in the liquid, if the buoyant force (or upthrust) exerted by the liquid is equal to the weight of the object, then the object will float in the liquid.
• Object rises and then float in the liquid, if the buoyant force (or upthrust) exerted by the liquid is more than the weight of the object.

#### THE PRINCIPLE OF FLOATATION

According to the principle of floatation, an object will float in a liquid if the weight of object is equal to the weight of liquid displaced by it.

weight of object = weight of liquid displayed by it

Density of Floating Objects:

• A body will sink a liquid if its density is greater than the density of the liquid.
• A body will float in a liquid if its density is less than the density of the liquid.
• A body will be in equilibrium at any submerged depth if the density of the body is equal to the density of the liquid.