# Pressure Class 10| SEE Physics Notes

## Pressure Class 10| SEE Physics Notes

### Pressure:

Definition: The pressure is the force applied on a per unit area.

• Formula of Pressure (P)= Force(F)/Area(A)
P= F/A
• Unit of Pressure= Force(F)/Area(A)= F/m²= pascal(pa).

Pascal(P): P=  F/A= 1N/1m²= 1/1 = 1pascal

• The 1 pascal is the pressure when 1N force is applied at 1m².

### Atmospheric Pressure:

Definition: The pressure exerted by the atmosphere on the surface of the earth is called Atmospheric Pressure.

• Diagram:

•  1 atmosphere= 760mm of Hg = 105 pascal.
• Atmospheric pressure is measured by a barometer. ### Liquid Pressure:

Definition: The pressure exerted on the bottom of the liquid container by the liquid is called Liquid pressure.

• P= d.g.h
P= density × g × height of the liquid column.
• Diagram:

Prove: p= d.g.h

• Statement: The liquid of density= ‘d’ is placed in a cylinder up to height ‘h’. The area of the bottom is ‘A’.
• Diagram: • Proof:
P= F/A
=m.g/A
=dvg/A  (∴m=dv)
=d.A.h.g/A  (∴v=A.h)
=dgh
Proved.

### Factor on which liquid pressure depends:

• P∝d: The liquid pressure is directly proportional to the density of the liquid.
• P∝h: The liquid pressure is directly proportional to the liquid column.
• P∝g: The liquid pressure is directly proportional to acceleration due to gravity. The value of pressure is more at the sea level than at the top of Mi. Everest level, etc.

Pascal’s Law: Pascal’s law states when pressure is applied at a point on the liquid enclosed in a vessel, a pressure is distributed in all direction.

• Diagram: • Diagram: ## Hydraulic Press or Hydraulic lift or Hydraulic brake:

• Principle: Pascal’s law
• Construction: ### Thrust:

Definition: The total perpendicular force exerted by a body on the surface is called thrust.

• Unit: Newton
• It is a vector quantity.
• Diagram: ### Uphrust:

Definition: The upthrust is the perpendicular upward force exerted by a fluid on the surface of an object.

• Diagram: ### Archimedes’ Principle:

Definition: According to this principle, when an object is immersed wholly or partially in liquid, it experiences upthrust. Equal to the weight of liquid displaced by an object.

• Demonstration: a) We take a weight of an object in air using spring balance.
b) We immersed the object in a liquid of eureka pot and take it weight.
c) The Displaced liquid is stored in a beaker of top balance, etc.
• Conclusion :
W= w1-W2
where,
W= upthrust
= loss in weight
= Weight of displaced liquid.
W1= Weight of an object in the air.
W2= Weight of an object in the water.

### Law of floatation or Principle of flotation.

• When upthrust is more than wright of the object, the object floats in liquid.
Diagram: • WHen upthrust is less than the weight of an object, object sinks in liquid.
Diagram: • When weight if an object is equal to the upthrust, the object sinks and floats below the upper for the surface of a liquid.
Diagram: ### Syringe:

• Principle: Atmospheric pressure
• Components: Needle, Storage cylinder, and piston, etc.
• Diagram: • Working Mechanism:
a) When we pull piston the vacuum is created between a piston and nozzle where the medicine or blood is filled in a storage cylinder.
b) When we push the piston, the pressure between the piston and nozzle is increased and medicine is pushed in our body.

### Water Pump:

• Principle: Atmospheric pressure
• Diagram: • Working Mechanism:
a) When Vacuum is created between valve-1 and valve-2, water is rushed up by opening the valve-2. (Piston down, hand up)
b) When pressure between valve-1 and valve-2  is increased valve-2 is opened and water is rushed up (Piston-up, handle down).

1. What is pressure? What are the factors upon which pressure depends? How do they affect?
Ans: The force acting pre-unit area is called Pressure.
Factor on which force depends are:
P∝d: The liquid pressure is directly proportional to the density of the liquid.
P∝h: The liquid pressure is directly proportional to the liquid column.
P∝g: The liquid pressure is directly proportional to acceleration due to gravity. The value of pressure is more at the sea level than at the top of Mi. Everest level, etc.
2. What is one pascal?
Ans: The One pascal is the pressure when 1N force is applied at 1m².
3. What is liquid pressure? What is the formula for liquid pressure?
Ans: The pressure exerted on the bottom of the liquid container by the liquid is called Liquid pressure.
The formula for liquid pressure is p= d.g.h.
Liquid pressure = density×g×height of the liquid column.
4. Prove p=d.g.h where p,d,g, and h have their respective meaning in liquid pressure.
Solution,
P= PRessure
d= Density
g= acceleration due to gravity
h= height if liquid column
Statement: The liquid of density= ‘d’ is placed in a cylinder up to height ‘h’. The area of the bottom is ‘A’.
Diagram: Proof:
P= F/A
=m.g/A
=dvg/A  (∴m=dv)
=d.A.h.g/A  (∴v=A.h)
=dgh
Proved.
5. Mention properties of liquid pressure.
Ans: The properties of liquid pressure are given below:
a) A liquid determines its own level.
b) Liquid pressure increases with density.
c) The liquid pressure is directly proportional to the depth from the free surface of the liquid.
d) Pressure applied to an enclosed fluid transmits equally in all directions, etc.
6. State pascals law.
Ans:  Pascal’s law states when pressure is applied at a point on the liquid enclosed in a vessel, a pressure is distributed in all direction.
7. What is a Hydraulic lift? On which principle does it work.
Ans: Hydraulic lift is a device which is used to lift light vehicles in the garage during their maintenance or services.
It works on a principle of Pascal’s law.
8. Where is a Hydraulic press used?
Ans: the Hydraulic press is used in a garage during their maintenance or service.
9. What is upthrust? What are the factors which affect upthrust?
Ans: The upthrust is the perpendicular upward force exerted by a fluid on the surface of an object.
The factors that affect upthrust are given below:
a) A density of a liquid.
b) Acceleration due to gravity.
c) A volume of an object, etc.
10. States pascal’s law. Write down any two application of this law.
Ans: Pascal’s law states when pressure is applied at a point on the liquid enclosed in a vessel, a pressure is distributed in all direction.
Two application of Pascal’s law is given below:
a) Hydraulic press,
b) Hydraulic break, etc.
11. Name the instruments that are constructed on the basis of Pascal’s law.
Ans: The instruments that are constructed on the basis of Pascal’s law are given below:
a) Hydraulic press,
b) Hydraulic break, etc.
12. Name the instruments which work on the basis of the principle of floatation. Also, write its uses.
Ans: The instruments which work on the basis of the principle of floatation with their uses are given below:
a) Hydrometer: It is used for the density of a liquid.
b) Lactometer: It is used to measure the density of milk.
c) Ship: It carries loads through water
d) Boat: It is also used to carry load through water, etc.
13. What will be the weight if displaced water if the load is added into the ship floating in the ocean?
Ans: The weight of the displaced water will be 2N if the load is added into the ship floating in the ocean is 5N.
14. If an object is immersed in water, at what condition it can float in water and at what condition it can sink in water?
Ans: If an object is immersed in water, it can float if the perpendicular upward force exerted by fluid in the surface of an object and it can sink in water if the perpendicular force exerted by a body on the surface.
15. A ship coming from sea enters the river, will it hull sink more or less in river water? Give reason.
Ans: A ship coming from sea enters the river, will it hull sink more or less in river water because the density of ship is more than river, therefore, the amount of water displaced by a ship is less than its weight and the upthrust applied by the water is not sufficient to make the ship float.

## Give reason:

1. Deep sea divers wear diving suits.
Ans: Deep sea divers wear diving suits because in the life jacket air is compressed to that it has very little weight but volume increases which the upthrust is more.
2. The foundation of a building is wider than the walls.
Ans: The foundation of a building is wider than the walls because the foundation has to withstand the whole load exerted by the wall and roofs of the building.
3. Camels can run faster than a horse in deserts.
Ans: Camels can run faster than a horse in deserts because camels have flat hoof which helps to decrease pressure in the desert but a horse hasn’t flat hoofs.
4. Why nail is made pointed?
Ans: A nail is made pointed because when a force is applied at the flat-end, the more pressure can be created by the pointed end on the wood.
5. It is easier to swim in ocean water.
Ans: It is easier to swim in ocean water because the density of our body is less than the water.

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