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| Blaise Pascal (1623-1662) |
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| Archimedes (267 BC to 212 BC) |
Pressure
Group
A
Pressure: Force applied perpendicular per unit area is called pressure. Its SI unit is N/m2 or Pascal.
1 Pascal: When 1 N force is applied perpendicular to 1m2
area, then the pressure is said to be 1 Pascal.
Liquid pressure: Force exerted by liquid per unit area of the
container is called liquid pressure.
Factors on which liquid
pressure depends:
a)
The depth of
the liquid column from the surface of liquid i.e. P α h
b)
The density of
the liquid i.e. P α d
c)
Acceleration
due to gravity i.e. P α g
Pascal's law of liquid
pressure: A pressure change at any point in a confined
liquid is transmitted throughout the liquid equally and perpendicularly in all
direction.
Application of Pascal's
law:
Hydraulic press: A hydraulic press is a machine press using a hydraulic cylinder to generate a
compressive force. It is used for forging, clinching, moulding, blanking, punching, deep drawing , and metal forming operations.
Hydraulic brake: It is a braking mechanism based on Pascal law to
control the speed of a machine. It is widely used in vehicles.
Hydraulic lift: A hydraulic lift is a type of machine
that uses a hydraulic apparatus to lift or move objects
using the force created when pressure is exerted on liquid in a piston.
Upthrust: The resultant upward force applied by a fluid to
the object partially or completely immersed in the fluid is called upthrust.
Archimedes' principle: When an object is partially or wholly immersed in a
fluid, it experiences an upthrust equal to the weight of the liquid displaced.
Law of floatation: A floating object displaces liquid equal to its own
weight.
Density: Mass per unit volume of a substance is called
density. Its SI unit is kg/m3.
Relative density: The ratio of the density of a substance to the
density of pure water at 00C.
|
Hydraulic press |
|
Hydraulic lift |
|
Hydraulic brake |
Hydrometer: A device based on law of floatation used to measure
the density of liquids.
Lactometer: A device used to measure the density or purity of
milk.
Atmospheric pressure: The pressure exerted by the atmospheric air per
unit area of the earth.
1 Atmospheric pressure = 760 mmHg = 1.013×105
Pa
Barometer: It is an instrument used to measure the atmospheric
pressure at any place.
Instruments based on atmospheric
pressure:
a) Syringe: It is a medical instrument used to inject
liquid medicine inside the body of patient through blood vessels.
b) Air pump: It is a device used to inflate tube of
vehicles, balls, balloons, etc.
c) Water pump: It is a pump used to lift underground
water.
Some important formulae:
Pressure(P) = F/A, where F = Force and A= Area
P=hdg
where, h=depth of liquid column, d=density of liquid
and g= acceleration due to gravity.
Where, F1 and F2 are the
forces on piston 1 and piston 2 while A1 and A2 are the
cross-sectional area of piston 1 and 2 respectively.
U=dgA(h2-h1)
Where, U= upthrust, d=density of liquid, A= area of
object, h2 = depth of liquid column upto the bottom of object while
h1 = depth of liquid column upto the top of the object.
Questions and Answers
1.
State law of floatation.
Law of floatation states that an
object floats on liquid medium only when it displaces the liquid equal to its
weight.
2.
What is upthrust or buoyancy?
When a body is partially or
wholly immersed in liquid, the liquid exerts an upward force to the body which
is called upthrust.
3.
State Archimedes principle.
Archimedes' Principle states that
when a body is partially or wholly immersed in liquid, the upthrust is equal to
weight of displaced liquid.
4.
Write two condition when a substance floats on liquid.
Two condition when a substance
floats on a liquid are:
i)
When the density of substance is lesser than the density of
liquid,
ii)
when the mass of the object is equal to the mass of liquid
displaced by it.
5.
Define pressure, write its formula and SI unit.
Ans: The perpendicular force per
unit area is pressure. Its formula is P =
and SI unit is pascal.
6.
Name two devices based on Pascal's law of liquid pressure.
Two devices based on Pascal's law
of liquid pressure are:
i) Hydraulic brake and ii)
Hydraulic lift
7.
What is lactometer?
Lactometer is a specially designed
hydrometer used to measure the density of milk.
8.
Mention any two factors which effect the upthrust.
Two factors that effect the
upthrust are: (i) density of liquid and (ii) acceleration due to gravity.
9.
State pascal's law.
It states that the liquid kept in
a container transmits equal pressure perpendicular to all direction.
10.
Write down the formula to find the relative density of an object.
The formula to find the relative
density of an object is:
Relative Density = mass of particular volume of a substance/Mass of same volume of water at 40C
or, Relative density =Density of a substance/Density of water at 40C
11.
What is one Pascal pressure.
When one Newton force is applied
perpendicularly in area 1m2 then pressure is called one Pascal
pressure.
12.
Name a device based on law of floatation. Also mention its one use.
Hydrometer is the device based on
the law of floatation. It is used to measure the density of liquid.
13.
On which principle does hydraulic brake based? State the principle also.
A hydraulic brake is based on the
Pascal's principle of liquid pressure. It states that the liquid kept in a
container transmits equal pressure perpendicular to all direction.
14.
By which two properties of liquid it is used in hydraulic brake?
Two properties of liquid by which
it is used in hydraulic brake are:
i)
Liquid cannot be compressed
ii)
liquid transmit pressure equally in all direction.
15.
What is hydrometer?
Ans: Hydrometer is a device which
is used to measure the density of liquids.
16.
What is the relationship between uptrhrust and the density of liquid?
The upthrust exerted by a liquid
is directly proportional to the density of liquid.
Upthrust α density of liquid
17.
What is hydraulic press?
Hydraulic press is a simple
machine based on Pascal's law of liquid pressure which converts small force
into large force and vice versa.
18.
Write the formula based on the Pascal's law.
The formula based on the Pascal's
law is: P1 = P2
or, F1/A1=F2/A2
Where P1 and P2
are pressure on small piston and large piston respectively of hydraulic
machine. F1 and F2 are the force applied on small and
large piston and A1 and A2 are the cross-sectional area
of small and large piston respectively.
19.
At what condition a body floats on liquid?
A body floats on liquid when it
displaces liquid equal to its own weight.
20.
What number will be shown by hydrometer if sunk in pure water?
Hydrometer will show 1 number if
it sunk in pure water.
21.
Which principle does hydraulic pressure obey? Write the principle.
Hydraulic pressure obey Pascal's
law of liquid pressure. It states that the liquid kept in a container transmits
equal pressure perpendicular to all direction.
22.
Define one torr pressure.
Ans: The unit of atmospheric
pressure equivalent to 1mm of Hg or 103.22 Pa. is one torr pressure.
23.
Define atmospheric pressure.
Ans: The pressure exerted by
atmospheric is called atmospheric pressure.
24.
Define normal atmospheric pressure, what is its value?
Ans: The pressure exerted by
atmosphere in one square meter area at sea level is called normal atmospheric
pressure. Its value is equal to 1.01 x 105 Pa or 760mm of Hg.
25.
What do you mean by 760mm of Hg?
Ans: It means that the height of
mercury column in barometer at sea level is 760mm while measuring atmospheric
pressure.
26. What is the relation between upthrust and
density of liquid.
Ans: The upthrust is directly
proportional to the density of liquid.
26.
Define density and relative density.
Ans: The mass per unit volume is
called density. The ration of density of a body to the density of water at 4°C
is called relative density.
Group B
27.
Write a condition in which the object having more density than liquid floats on
liquid.
When the object can displace
liquid equal to its own weight then the object having more density than liquid
floats on liquid.
28.
Why the ship can carry more load on the salty water than fresh water?
Ans: In salty water the density
is more so that upthrust becomes more as we know that upthrust is directly
proportional to the density of liquid as a result the ship can carry more load
on salty water.
29.
It is easier to swim in sea water than in fresh water. Why?
The sea water has more density
than the pure water. Due to this, when a man swims, the upthrust acting on him
due to sea water is greater than the upthrust acting on him by fresh water.
Because of this reason, it is easier to swim in sea water than in fresh water.
30.
Why it is easier to pull a bucket of water
from well until it is inside the water but difficult out of water?
When a bucket of water is in
water, its weight is reduced due to the action of upthrust of water. But, when
it is pulled out of water, its weight is increased due to the absence of
upthrust of water and becomes heavy. Hence, it is easire to pull a bucket of
water from well until it is inside the water but difficult when it is out of
water due to the upthrust of water.
31.
What difference is observed if an egg is immersed in pure water and in
concentrated solution of salt? Write with reason.
An
egg sinks in pure water but floats on the concentrated salt solution. This is
because the density of salty water is more than the fresh water, as we know that
the upthrust is directly proportional to the density. so being more upthrust
due to salty water, an egg floats on it but sinks in fresh water.
32. It is easier to lift a heavy
stone inside water than air, why?
When a stone is inside water, its
weight is reduced due to the upthrust exerted by water. But, when it is in air,
its weight is increased due to the absence of upthrust of water and becomes
heavy. Hence, it is easier to lift a stone in water but difficult to lift in
air.
33. An iron nail sinks in water but
floats on mercury, why?
An
iron nail sinks in water because the density of iron nail is more than water
but it floats on mercury because the density of iron is lesser than mercury.
34.
What is the difference between an empty sheep and loading ship moving in sea
water?
A loaded ship has larger mass and
it displaces more water to float on water but an empty ship has less mass and
it displaces less amount of water. Thus the hull of an empty ship sinks less
than the hull of a loaded ship.
35. Studs are made on the sole of
football player's boot, why?
The
area of the studs of the football player's boot is less, we have pressure is
inversely proportional to the area. Hence, more pressure is created on the
ground by the studs. Due to high pressure the shoes properly get stuck with the
ground and does not allow the player to slip during the game.
36. Hydraulic press is called an
instrument for multiplication of force. Why?
Hydraulic
press is called an instrument for multiplication of force because the force
applied on smaller piston multiplies and a large force is exerted on large
piston. According to pascal's law;
Pressure
on large piston (P1) = Pressure on small pistion (P2)
or, Force on large piston (F1)/Area of large piston (A1) = Force on small piston (F2) /Area of small piston(A2)
From
the expression, we can say that the force exerted on large piston is given by
the product of pressure on small piston and area of large piston. Hence due to
this amplification, the applied force is multiplied in the hydraulic press.
37. Pressure applied on a liquid
enclosed in a vessel will be transmitted equally in all direction perpendicular
to the surface. Which law is explained by this statement? Name the instrument
which works on the basis of this law?
Pascal's
law of liquid pressure is explained by this statement. The instrument which
works on this principle is hydraulic press.
38. Write the difference in
floatation of lactometer in pure milk and sugar dissolved milk.
Sugar
dissolved salt has more density than that of pure milk. Sugar dissolved milk
exerts more upthrust of lactometer than pure milk. So, the stem remains more
above the milk in sugar dissolved milk than pure milk.
39. What is the difference between
the immersion of hydrometer in pure water and salty water?
Hydrometer
immerse more in pure water than in salty water because the density of salty
water is more than that of pure water, which implies upthrust due to salty
water is greater than pure water and hydrometer immerse more in pure water than
salty water.
40. "The weight of displaced
liquid is equal to the weight of floating objects." Which law does this
statement belong to?
This
statement belongs to law of floatation.
41. What difference will you get
from the flying of air filled balloon and the hydrogen filled balloon?
An
air filled balloon is heavier than that of hydrogen filled balloon since the
density of air is heavier than hydrogen. Hence, upthrust due to air on the
hydrogen filled balloon is more thus, it flies to the greater height than that
of air filled balloon.
42. What is the effect of density of
a liquid on floatation of an object?
Floatation
of an object increases with the increase in density of liquid.
43. Why does a stone sink in water?
A
stone sinks in water because its density is lesser than the density of water
and the upthrust exerted by water is lesser than the weight of stone.
44. Write the relation between
upthrust and volume of displaced liquid. Lifting a stone in water is felt to be
comparatively lighter, why?
Upthrust
is directly proportional to the volume of liquid displaced. Repeated.
45. The ship made by iron floats in
water, but an iron nail sinks, why?
The
shape and size of ship made by iron is so made that if can displace the liquid
equal to its weight. So a ship can float in water, but iron nail can't displace
the liquid equal to its weight so it sinks.
46. In given figure, which pressure
is greater, AB or CD, why?
Pressure
on Face CD is greater than AB because the pressure is directly proportional to
the depth and the depth is more on face CD.
47. The weight of any object
decreases inside water. Give reason. How much will an object lose in water?
Upthrust
force exerted by water reduces the downward force on the object. When an object
sinks in water the weight of object is lost and becomes light. So weight of an
object decreases inside water. An object lose weight equal to the weight of
water displaced by it.
48. A ship coming from sea enters
the river, will its hull sink more or less in river water? Give reason.
A
ship coming from sea enters the river, its hull will sink more in river water.
This is because the density of river water is lesser than the density of sea
water and it exerts less upthrust than sea water. As a result, hull of ship
will sink more in river water.
49. When a ball is pressed in water,
why does it try to come up?
When
the ball is pressed in water, it tries to come up because it experiences an
upthrust more than its weight.
50. What is the relation of upthrust
of a liquid and its density?
Upthrust
is directly proportional to the density of liquid. It means Upthrust increases
with the increase in density of liquid and vice versa.
51. What will be the effect in the
weight of displaced water if load is added into the ship float in the ocean?
Write with reason.
The
weight of water displaced increases and the hull will sink more when load is
added into the ship float in the ocean. This is because floating object
displaces liquid equal to their own weight. Here, when load is added into the
ship weight of ship increases and in order to float on water, it has to
displace more water.
52.
If an object is immersed in water, at what condition can it float in
water, and at what condition does it sink in water?
If
an object is immersed in water, it floats on water when its density is lesser
than the density of water or upthrust of water is more than the weight of the
object. It will sink in water, when its density is more than the density of water or if the upthrust
exerted by water is lesser than the weight of the object.
53.
Constant
weight hydrometer contains heavy bulb and narrow stem, why?
The
weight of hydrometer contains heavy bulb to float in the liquid vertically and
the stem is made narrow for greater sensitivity.
54.
The ice made of water floats on water, why?
The density of ice is 0.9g/cm3
while the density of water is 1g/cm3. Thus the density of ice is
lesser than the density of water. So, it floats on water.
55.
Air is filled in the tyres of bicycle, motorcycle, car, bus, etc. why ? Give
reason.
Ans: The air inside the tyres
lifts up the vehicles on the ground so that pressure of vehicles to the ground
decreases so air is filled in the tyres of vehicles.
56.
Mention any three applications of Pascal's law.
Ans: Any three applications of
Pascal's law are given below:
(i) Hydraulic press
(ii) Hydraulic lift
(iii) Hydraulic brake.
57.
Define hydraulic press and hydraulic lift.
Ans: The device which is used to
press the metal, grains etc and works on the basis of Pascal's law is called
hydraulic press.
Hydraulic lift : The device which
is used to lift the heavy load with small effort and works an the basis of
Pascal's law is called hydraulic lift.
58.
Write the use of hydraulic press and hydraulic lift.
Ans: The hydraulic press is used
to obtain the oil from seeds and also uses to press metal in order to convert
metallic sheath.
Hydraulic lift is used to lift
the heavy load with small effort by cranes.
59.
What are the functions of hydrometer?
Ans: Followings are the functions
of hydrometer.
(i) It measures the density of
substance.
(ii) It measures the relative
density of substances.
60.
Food gets cooked faster in pressure cooker, why?
Ans: The water boils when the
vapour pressure becomes equal to atmospheric pressure, inside the pressure
cooker the pressure becomes more so that water boils at high temperature as a
result pressure cooker cooks food faster.
61.
What should be the weight of displaced liquid to float an object of 375 kg.
Ans: According to law of
floatation the weight of displaced liquid should be 375 kg to float on that
liquid.
62.
Above the certain height in the sky, the aeroplane can't fly, why?
Ans: The aeroplane flies due to the difference
of air pressure created by its fans, above the certain height in the sky there
is absence of air, so the aeroplane can't fly above the certain height.
63.
In given figure the tanks A and B both contain equal amount of water but the
height of water in tank A is more than tank B, on which bottom the water exerts
more pressure, why?
Ans: The bottom of tank A
experiences more liquid pressure. The liquid pressure is directly proportional
to the height or depth of liquid column when acceleration due to gravity and
density remain constant and the depth of liquid is more in tank A. So, the
bottom of tank A experiences more pressure.
64. In given figure, tank A and tank B contain salty water and fresh water respectively. Both tanks contain the liquid upto equal height. Which bottom experiences more liquid pressure out of A and B? Why?
Ans: The bottom of tank A
experiences more liquid pressure. The liquid pressure is directly proportional
to the density of liquid when depth or height of liquid column and acceleration
due to gravity remain constant. In liquid of tank A the density is more than
the liquid of tank B. So. bottom of tank A experiences more liquid pressure.
65.
Two tanks A and B contain equal amount of water with equal height, but tank A
is placed at equator while tank B is placed at pole, which bottom experiences
more liquid pressure, why?
Ans: The bottom of tank B
experiences more liquid pressure because the liquid pressure is directly
proportional to the acceleration due to gravity when height and density remain
constant, and we know that the value of acceleration due to gravity is more at
poles than equator.
66.
Two tanks A and B contain equal amount of oil with equal height but the
temperature of tank A is 90°C and the temperature of tank B is 10°C, which
bottom experiences more liquid pressure, why?
bottom of tank B experiences more
liquid pressure. The liquid pressure is directly proportional to the density
when height of liquid column and acceleration due to gravity remain constant
and the oil of tank B has more density due to its less temperature than liquid
of tank A. So, the bottom of tank B experiences more liquid pressure.
67.
It is easier to cut with sharp knife than blunt one, why?
Ans: The area of sharp knife is
less than area of blunt one, we have pressure is inversely proportional to the
area i.e. Pα
68.
Back wheels of the tractors are made wider, why?
Ans: Tractors are used to plough
in field, as the wider wheels have more area, it exerts less pressure because
pressure is inversely proportional to the area i.e. Pα
69.
Dams are made wider at the bottom, why? Give reason.
Ans: Dams are made to hold the
water, at bottom the liquid pressure is more as we know that liquid pressure is
directly proportion to the depth of liquid i.e. Pαh when density and
acceleration due to gravity remain constant, to hold the more pressure at
depth, the bottoms are made wider.
70.
It takes less time to fill the bucket from the tap of lower floor than the tap
of upper floor, why ? Give reason.
Ans: At tap of lower floor the
depth or height of liquid column is more than the tap of upper floor. As we
know that liquid pressure is directly proportional to the depth of liquid i.e.
P α h when density and acceleration due to gravity remain constant, so water
comes with more pressure from the tap of lower floor, as a result it takes less
time to fill a bucket from the tap of lower floor than the tap of upper floor.
71.
Camel can walk on desert but horse can't, why? give reason.
Ans: The hoof of camel is boarder
than hoof of horse, so camel exerts less pressure while walking on desert, as
we know that pressure is inversely proportional to the area, i.e. Pα 1/A , So the camel can walk easily on the desert
but horse can't.
72.
The blood pressure of our body is more at feet than at brain, why? Give reason.
Ans: As we know that liquid
pressure is directly proportional to depth or height liquid column. When
acceleration due to gravity, and density remain constant at feet, the height of
liquid column or height is more so blood pressure at feet is more than blood
pressure at brain.
73. In tank given in figure, which bottom experiences more liquid pressure out of A and B.
Ans: Both bottoms experience
equal liquid pressure as the liquid pressure is directly proportional to the
depth or height of liquid when density and acceleration due to gravity remain
constant and both B bottoms experience
the pressure of liquid of same height.
74.
Why the dead body of human floats in water?
Ans: Where person gets drawned in
water, he/she sinks as the cavity present inside the body is filled with water.
After some time it starts to decompose by the decomposer and produces the gases
like CH4, N2 etc, These gases decreases the density of
the dead body. Hence the dead body floats in water.
75. Why does an egg float in salty
water?
Ans:
The density of salty water is more than the fresh water, as we know that the
upthrust is directly proportional to the density. so the egg floats in salty
water.
76. From Archimedes principle give
reason why a balloon filled with hydrogen gas flies up?
Ans: The balloon filled with hydrogen gas can easily displace the air more than its weight. The upthrust becomes more than the weight of balloon. So it flies up.
thanks a lot
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