This is the PowerPoint presentation for students of grade 10. Here you will get a chance to know about the Laws of pressure, liquid pressure, Upthrust, Archimede's Principle, Density and Thermometer. Everything is briefly explained as notes with proper experimental verification, examples, and some other interesting facts about this lesson.

1. CHAPTER 2
PRESSURE

2. Blaise Pascal ( 1623 AD )

3. Pressure
• Force per unit area is called pressure. Its SI unit is
called Pascal.
• Pressure (P)= Force (F)/Area (A)
• Also Liquid Pressure (P)= hdg
• where, h=Height of liquid
column
• d=density of liquid
• g=Acceleration due to
gravity

4. Laws of Liquid Pressure
• Liquid cannot be compressed.
• Liquid pressure can be transmitted equally to all the
direct.

5. Pascal’s law
• When pressure is applied on a liquid enclosed in a
vessel, it is transmitted equally and perpendicularly
to all the direction.

7. Experimenta
l Verification
of Pascal’s
law

8. • Consider a vessel filled with water and fitted with
pistons A,B,C and D as shown in the figure. If a
pressure is applied to piston A, other pistons B, C
and D move equally outward. This, proves that liquid
pressure is transmitted equally to all direction.

9. Application of Pascal’s Law
1. Hydraulic press
2. Hydraulic lift/Jack
3. Hydraulic Brake

10. Hydraulic press
• Hydraulic press is machine based on pascal’s law
which multiply force and helps to press jute, cotton
etc in industries.
• Uses:
• 1. it is used to produce sugarcane juice from
sugarcane.
• 2. it is used make bales of cotton.
• 3. it is used to press jute, cotton etc.

11. Hydraulic Press

12. Let, F1 = Force applied in small piston
A1= Area of cross- section of small piston
F2 = Force exerted in large piston
A2 = Area of cross – section of large piston

13. In small piston, P1 = F1/ A1 …………….i
In large piston, P2 =F2 / A2 …………….ii
From pascal’s law, P1 =P2
F1/A1 = F2 / A2
F2 = F1 / A1 × A2 …………….iii
Here, F2 is directly proportional to A2
so, greater the surface area of large piston, greater
will be the force multiplied.so hydraulic press is also
called force multiplier.

14. Hydraulic lift / Jack
• It is machine based on pascals law that multiplies
force and helps to lift heavy vehicles and heavy
loads.
• Uses:
• 1. it is used to lift heavy loads in industries, factories.
• 2. it is used to lift heavy vehicles in garage.
• 3. it is used to lift heavy loads in construction sides.

16. Hydraulic Brake
• It is a machine based on pascals law that multiplies
force and helps to stop the running automobiles.
• Uses:
1. It is used to stop running vehicles, aeroplanes,
motorbike etc.
2. It is used to stop running automobile.

18. Principle of Hydraulic
Machine
• It states, “A large force is developed on a larger
piston when a small effort is applied on the smaller
piston”.

19. Upthrust/ Buoyancy Force
• The resultant upward force exerted by a fluid or
liquid on an object immersed in the liquid is called
upthrust. It is denoted by “U”. Its SI unit is Newton
“N”.
• Upthrust(U)=vdg , where, v= volume of object
• d= density of liquid
• g=Acceleration due to gravity
•

20. Upthrust
• Upthrust=Weight in
air-weight in water

21. • Let, w1 = weight in air
• w2 = weight in water
• Therefore, loss in weight = w1 – w2
• Loss of weight = upthrust = w1 – w2
• So, U = W1 – W2

22. Factors Affecting Upthrust
1. Volume of immersed body. ( U α V )
2. Density of liquid ( U α d )
3. Acceleration due to gravity ( U α g )

23. Archimedes’ principle
• It states that, “When a body is partially or wholly
immersed in a liquid, it experiences an upthrust
which is equal to the weight of liquid displaced by
it”.
• Upthrust= weight of displaced liquid.

24. Experimenta
l Verification
of
Archimedes
Principle

25. • Let w1 = weight in air
• w2 = weight in liquid
• Upthrust ( U ) = w1 – w2
• Let, weight of beaker = w3
• weight of beaker + displaced liquid = w4
• Therefore, weight of displaced liquid = w4 – w3

26. • Experimentally it was found that
• W1 – w2 = w4 – w3
• Therefore, upthrust = weight if displaced liquid.

27. Law of Floatation
• When a body is floating in the liquid it displaces the
liquid equal to its weight.
• Therefore, weight of floating body = weight of
displaced liquid

29. Applications of Archemides
Principle
• It is used for finding volume of irregular substance.
• It is used for finding weight of unknown substance.
• It is used in ship and hot air ballon.

30. Conditions of Floating and
Sinking
• When a body floats or sinks, two forces act upon it.
They are : a) weight of body ( downward )
b) upthrust ( upward )
There are 3 conditions of floating and sinking. They are:
1. When the weight of body is greater than the
upthrust, the body sinks. ( W > U ). It means if density
of object is more than liquid, the object sinks in the
liquid.

31. 2. When the weight of body is equal to the upthrust,
the body floats inside the liquid. ( W = U ). It means if
density of object is equal to liquid, the object floats
inside the liquid.
3. When the weight of body is less than the upthrust,
the body floats. ( W < U ). It means if density of object
is less than liquid, the object floats in the liquid.

33. Application of Law of
Floatation
• It is used for floatation of submarine.
• It is used in floatation of iceberg, ship.

34. Density
Mass per unit volume of a substance is called density.
Its SI unit is kg/m3 .
Density ( d ) = mass( m )/ volume ( v )
Note:
1. Density of water is maximum at 4o C.
2. Density of water is 1000 kg/m3 . What do you mean
by it?
- It means 1m3 volume of water has mass 1000 kg.

35. Relative density ( R.d )
• The ratio of density of a substance to the density of
water at 4o C is called relative density.
• Relative density ( Rd ) = density of substance
• density of water at 4oC
• Note:
1. Relative density of silver is 10.5. what do you mean
by it?
- It means silver is 10.5 times heavier than water.

36. 2. Relative density of ice is 0.9. What do you mean by
it?
- It means ice is 0.9 times lighter than water.

37. Notes
• 1. an egg
sinks in fresh
water but
floats in the
concentrated
solution of
salt and
water. Why?

38. • It is because fresh water has less density than
concentrated salt solution. So, concentrated salt
solution gives more upthrust than fresh water, ( u α
d ).so, egg floats in concentrated salt solution.

39. • 2. an iron nail sinks in water but ship made by same
iron floats in water carrying heavy loads. Why?

40. • - It is because ship covers large space and it has
hollow space. So, entire density of ship lowers and
becomes less than water. So, ship can displace water
equal to its weight and floats.

41. • 3. weight of body decreases in water. why?
- It is because water gives maximum upthrust than air.
So, weight of body decreases inside water.
• 4. it becomes easy to swim in seawater. Why?
-It is because sea water contains maximum salt. So,
density of sea water is more. Sea water gives more
upthrust ( u α d ) and hence it becomes easy to swim in
sea water.

42. Atmospheric Pressure
• Pressure exerted by atmospheric air is called
atmospheric pressure. The pressure exerted by
atmospheric air at sea level is called standard
atmospheric pressure. It is about 760mmHg. It is also
1×105 pa.
• Since, p=hdg
• =0.76×13600×9.8
• = 1.01×105 pa

43. Experiment
• To demonstrate that atmospheric air exerts pressure.
• Let us consider a tin can and put a little water in the
tin can. Boil the water in the tin without closing its
mouth. Vapour is released outside from the can.
Close the mouth of tin can which lead tightly.
Remove the tin can from the fire and cool it by
pouring cold water over it. The tin can gets crushed.
It gets shrinking inward. This proves that,
atmospheric pressure exerts.

44. Air exerts
pressure

46. Measurement of Atmospheric
Pressure
• The atmospheric pressure can be measured with the
help of device called barometer. It was invented by
Italian physicist Evangelista Torricelli in 1643.

47. Mercury Barometer
• Construction: it consists of glass tube of 100cm long
inverted over a trough containing mercury ( Hg ). Pure
mercury is filled in it completely. Air bubbles if present,
are removed by closing the open end of the tube by a
thumb and inverting and shaking several times. Above
the mercury surface in the tube, a vacuum is created
which is called Torricellian vacuum.
• Working: when mercury barometer is taken to a certain
place the atmospheric pressure pushes the mercury in
the trough downward and the level of mercury increases.
The level of mercury increases or decreases according to
the height and atmospheric pressure.

48. Mercury
Barometer

50. Advantage of mercury
1. The mecury doesnot stick on the wall of glass tube.
2. Its density is high so the length of the glass tube in
barometer will be short.
3. It is shiny and read easily.

51. Disadvantage
• It is not portable size.
• It is to be kept always vertically to take the reading.

52. Use of Mercury Barometer
1. It is used to determined pressure in laboratories.
2. It is used in weather station to read atmospheric
pressure.

53. Practical application of
atmospheric pressure
• Syringe
• Water pump
• Air pump

54. Syringe
• It is an instrument which is used by doctors or nurses
in hospitals to give injection to their patients. It
works on the principle of atmospheric pressure.
• Construction:
It consists of a piston , a barrel and a narrow method
tube in the form of a needle.

55. Working
When piston is pulled outside, volume inside
the barrel increases but pressure inside it decreases .
so, large atmospheric pressure pushes the medicine
into the syringe. This is called upstroke.
When piston is pushed inside , volume inside
the barrel decreases but pressure inside it increases. So
it helps to push the medicine into the patient’s body.
This is called down stroke.

56. Syringe

57. Water Pump / Hand Pump
• It is an instrument which is used in rising water from
underground. It is based on the principle of
atmospheric pressure.
• CONSTRUCTION:
• It consists of a piston with a handle, a barrel, and a
metal pipe. There are two valves. One valve ( V1 )
lies in the piston which moves up and down.
Another valve ( V2 ) lies in the base of barrel which
goes well into the water reservoir.

58. Working
• When handle of hand pump is pushed down, the piston
moves up. So,volume of barrel in between two valves
increases and pressure in it decreases. So , valve v1 of
piston gets closed and valve v2 of base of barrel gets
opened. So, water from underground comes up in the
barrel due to large atmospheric pressure and water
comes out from nozzle. This is called upstroke.
• When handle of hand pump is pulled up, the piston
moves down. So,volume of barrel in between two valves
decreases and pressure in it increases. So , valve v1 of
piston gets opened and valve v2 of base of barrel gets
closed. So,water comes up to cylinder through valve v1.
This is called downstroke.

59. Working

60. Handpum
p

61. Air pump
• A bicycle pump or air pump is a type of positive
displacement pump specifically designed for inflating
bicycle tyres.
• CONSTRUCTION.
• it consists of three main parts . They are the piston,
cylinder and nozzle.

62. Working
• A bicycle pump functions via a hand operated piston.
During the upstroke,volume inside cylinder increases
and pressure in it decreases. So, this piston draws air
through a one way valve into the pump from the
outside. During the down stroke, volume inside the
cylinder decreases and pressure in it increases. So,
the piston then displaces the air from the pump into
the bicycle tyre.

63. Air pump