# Pressure in liquid

Question 1 what is meant by the term buoyancy?

Question 2 Why does a block of wood held under water rise to the surface when released?

Question 3 Define buoyant force?

Question 4 Name the factors on which buoyant force depends?

Question 5 In which direction does the  buoyant force on an object due to a liquid act?

Question 6 Name the factors which makes heavy object appear light when immersed in a liquid?

Question 7 What is the cause of  buoyant force?

Question 8 Why do we light on our feet while standing in a swimming pool with water up to our armpits?

Question 9 Why big boulders can move easily by flood?

Question 10 State Archimedes’s principle?

Question 11 When a boat is partially immersed in water,it displaces 600 kg of water.How much is the buoyant force acting on the boat in newtons?

Question 12 A mug of water appears light as long as it is under water in the bucket than when it is buoyant force acting on the boat in newtons?

Question 13 What are fluids.Give example?

Pressure in Liquids
Those substances which can flow easily are called as Fluids.
All liquids and gases are fluids.
A fluid exert pressure in all direction.

Buoyancy
When a piece of cork or bottle is held below the surface of water by applying the force of our thumb and then released,the cork or bottle immediately rises to the surface.it appears as if some upward force is exerted by water on cork or bottle which pushes it to the surface.
If we lift a stone lying at the bottom of a pond,it appears to be light as long as it is being lifted inside water.But as soon as stone is lifted out of water into air,the same stone feels to be much heavier.This means that some upward force acts on the stone when it is immersed in water and makes it feel lighter.

As long as the mug filled with water remains immersed in bucket full of water,it appears to be light and hence easy to lift.But as soon as the mug filled with water is lifted out of bucket of water,it feels much heavier.As long as the mug filled with water is inside the water surface,some upward force acts on it which reduces its effective weight and make it appear lighter.

The object appear to be less heavy in water because the water exerts upward force on them.

Every liquid exerts an upwards force on the object immersed in it.

The tendency of a liquid to exert an upward force on the object immersed in it is called buoyancy.
The upward force acting on an object immersed in a liquid is a called buoyant force.

It is due to upward buoyant force exerted by a liquid that the weight of an object appears to be less in liquid than its actual weight in air.

The upward force exerted by liquid is called upthrust.

It is due to buoyant force we are able to swim in water,ship floats in water.

Water exerts force on sides,top,bottom of mug.The sideways forces exerted by water being equal and opposite cancel out.There is a force of water acting on the top of mug and force of water acting on the bottom of mug.The pressure exerted by a liquid increases with depth and acts in all direction.
As the top of mug is at greater depth in water,so it experiences less force downwards.
As the bottom of mug is at greater depth in water,so it experiences more force on the mug in upward direction.
Thus there is net force on the mug in upward direction.This net upward force acting on the mug is buoyant force.

As we lower the object into a liquid,greater upward pressure on liquid underneath it provides an upward force.

The magnitude of buoyant force acting on an object immersed in a liquid depends on
1)Density of liquid
2)Volume of object immersed in liquid

As the volume or density of object immersed inside the liquid increases,buoyant force also increases.

mass
Density=————
Volume

If the buoyant force exerted by liquid is less than weight of object,the object will sink in liquid.
If the buoyant force exerted by liquid is equal to the weight of object,the object will float.An object will float in a liquid if upward buoyant force it receives from liquid is great enough to overcome the downward force of its weight.

Archimedes Principle

When a solid object is immersed or dipped in a liquid,an upward buoyant force acts on the object.The magnitude of buoyant force is given by Archimedes principle.

When an object is wholly or partially immersed in a liquid ,it experiences a buoyant force or upthrust which is equal to the weight of liquid displaced by the object.
Buoyant Force(or upthrust)acting on an object = Weight of liquid displaced by
that object

For Ex:If a stone,on being immersed in water,displaces 10 newtons weight of water,then according to archimedes principle,buoyant force will be equal to 10 newton.

Applications
1)It is used in determining the relative density of a substance.
2)The hydrometers used for determining the density of liquids are based on archimedes principle.
3)The lactometers used for determining the purity of milk.
4)It is used in designing ships and submarines.