Pascal's Law, Archimedes' principle, Law of floatation, Atmospheric pressure, Mercury barometer, Air pump, Syringe, Hand pump

1. Pressure
• Pressure on the surface can be defined as the force (weight) acting
perpendicularly on the unit area of that surface.
• The SI unit of pressure is newton/metre2 which is also called Pascal (Pa) to
honor the French scientist Blaise Pascal.
• If the force of one Newton acts on one square meter area, the pressure acting
on it is 1 pa.
• PRACTICALAPPLICATIONS OF PRESSURE:
• The base of the dams is made wide to reduce the pressure exerted by the dam
structure and also to withstand the enormous pressure of the stored water.
• The base of walls of buildings, bridges and temples is made wider to reduce
the pressure exerted by them.
• The tyres of buses and trucks have broad and double wheels so that the
pressure on the tyres is reduced
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2. Liquid Pressure
• The force per unit area exerted
by a gas or liquid over a
surface in a direction
perpendicular to that surface
• The force exerted per unit area
.i.e. pressure (P) = force (F)
/area(A) = ρAhg/A=ρgh
• i.e. P= ρgh
• Factors affecting the pressure
at a point in a liquid:
• Depth of the point below the
free surface (h)
• Density of the liquid (ρ)
• Acceleration due to gravity (g)
• Liquid Pressure
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3. Pascal’s Law
• Pascal’s law: Transmission of
pressure in liquids
• Pascal’s law states that the
pressure exerted at any point in a
liquid enclosed in a container is
transmitted equally in all directions
throughout the liquid. The
transmitted pressure, acts with
equal force, on every unit area of
the containing vessel in a direction
at right angles to the surface of the
vessel exposed to the liquid.
• Pascal’s Law is applicable to both
solids and liquids.
• The mathematical representation
of the law is as follows:
• F = PA; where F=applied force,
P=pressure transmitted, and
A=cross-sectional area.
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4. Application of Pascal’s Law
• A hydraulic lift is versatile in its utility. It has a hydraulic
apparatus which is used to lift heavy objects. In the case of
hydraulic lifts, force applied creates “lift” and “work.”
• Hydraulic jacks, which come under the category of a closed
container, follow the principle of Pascal’s Law. They are used
to lift heavy bodies.
• One of the most common examples of Pascal’s Law is the
hydraulic braking system present in the automobiles. Every
time you see a car come to a halt, the principle of Pascal’s Law
comes into action.
• Hydraulic pumps, which convert mechanical energy into
hydraulic energy, facilitate the movement of a fluid, and here,
yet again, Pascal’s Law comes into play.
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5. Hydraulic Lift
Hydraulic Brake
Hydraulic Jack
Hydraulic Pump
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6. Hydraulic Jack
Construction:
• As shown in the figure, it consists
of two cylindrical vessels C1 and
C2 connected to each other by a
tube T having a valve V. The
piston P1 in the narrow cylinder
C1 is attached to a lever and
piston P2 of the wider cylinder C2
has a platform for lifting the
vehicle. The vessels filled with a
liquid (like water).
• Principle: Based on the Pascal’s
law of liquid pressure.
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7. Pascal’s Formula
Working:
• When handle H of the lever is
pressed down by applying the effort,
valve V opens because of increase in
pressure in the cylinder C1.
• The liquid runs from the cylinder C1
to, the cylinder C2.. As a result, the
piston P2 rises up and it raises the
car placed on the platform.
• Then, the car reaches the desired
height, the handle H of the lever is
no longer pressed.
• The valve 'V gets closed (since the
pressure on either sides of the value
becomes same) so that the liquid
may not run back from the cylinder
C2 to the cylinder.
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8. Pascal’s formula
• Let, A1 is the cross
sectional area of piston
P1 and A2 is the cross
sectional area of the
piston P2. When an effort
F1 is applied on the
piston P1, the down ward
pressure in it is given by:
P1 = F1/ A1
• Then, the pressure
transmitted to Piston P2
is same as of piston P1.
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9. Buoyancy/Upthrust
• The term buoyant force refers to the upward perpendicular
force that a fluid exerts on an object that is partially or
completely immersed in the fluid.
• The buoyant force comes from the pressure exerted on the
object by the fluid. Because the pressure increases as the
depth increases, the pressure on the bottom of an object is
always larger than the force on the top - hence the net
upward force. The buoyant force is present whether the
object floats or sinks.
• Unit: newton (N)
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10. Measurement of Upthrust
U
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11. Factors affecting upthrust
• Depends upon:
• Directly proportional
to the density of the
liquid (p)
• Directly proportional
to the depth from the
surface (d)
• Directly proportional
to the acceleration
due to gravity of the
place (g)
=pdg
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12. Archimedes’ Principle
Statement:
It states that when a
body is immersed
fully or partially in a
fluid, it experiences
an upward thrust
equal to the weight
of the fluid displaced
by it.
i.e., upthrust = weight
of displaced fluid
Applications:
• Lactometer
• Hydrometer
• Ships and
submarines
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13. Measurement of Archimedes’ Principle
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14. Law of floatation
Law of floatation states that the weight of a floating body is equal to the
weight of the displaced liquid. A body floats on a liquid when the density
of the body is equal to the density of the liquid in which the body is kept.
i.e. the weight of floating body = weight of displaced liquid
It is a special condition of Archimedes' Principle.
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15. Applications
• Submarines: Ballast tanks in submarine is
filled with sea water so that it sinks.
• Floatation of Iron ship
• Icebergs floating on water
• Swimming/Floatation of man
• Hot air balloon
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16. Atmospheric Pressure
The air around you has weight, and it presses against everything it touches.
That pressure is called atmospheric pressure, or air pressure.
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17. Anjan Nepal

18. Effects of Atmospheric Pressure
• Atmospheric pressure drops as altitude increases. As the pressure
decreases, the amount of oxygen available to breathe also decreases. At
very high altitudes, atmospheric pressure and available oxygen get so low
that people can become sick and even die.
• Mountain climbers use bottled oxygen when they ascend very high peaks.
They also take time to get used to the altitude because quickly moving
from higher pressure to lower pressure can cause decompression sickness.
Decompression sickness, also called "the bends", is also a problem
for scuba divers who come to the surface too quickly.
• Aircraft create artificial pressure in the cabin so passengers remain
comfortable while flying.
• Atmospheric pressure is an indicator of weather. When a low-pressure
system moves into an area, it usually leads to cloudiness, wind,
and precipitation. High-pressure systems usually lead to fair, calm weather.Anjan Nepal

19. Mercury Barometer
• The classic mercury barometer is
designed as a glass tube about
100 cm high with one end open
and the other end sealed.
• The tube is filled with mercury.
• This glass tube sits upside down
in a container, called the
reservoir, which also contains
mercury. No air should be
present.
• The mercury level in the glass
tube falls, creating a vacuum at
the top called Toricellian vacuum.
(The first barometer of this type
was devised by Italian physicist
and mathematician Evangelista
Torricelli in 1643).
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20. Mercury Barometer
• The barometer works
by balancing the weight of
mercury in the glass tube against
the atmospheric pressure, much
like a set of scales.
• Atmospheric pressure is basically
the weight of air in the
atmosphere above the reservoir,
so the level of mercury continues
to change until the weight of
mercury in the glass tube is
exactly equal to the weight of air
above the reservoir.
• Once the two have stopped
moving and are balanced, the
pressure is recorded by "reading"
the value at the mercury's height
in the vertical column.
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21. Advantages of Mercury Barometer
• It is the heaviest liquid with high density. Therefore it rises to a
height of only 76 cm to balance the atmospheric pressure. So
the length of glass tube required is not more than 1 meter.
• It gives more accurate reading as it does not stick to the glass.
• It is opaque and shiny and hence can be seen easily through
glass.
• Mercury forms very little or no vapor above mercury in the
glass tube.
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22. Disadvantages
• It is not of portable size. So,
it can’t be carried from
place to another.
• It is to kept always vertical
to take reading.
• It may be broken easily as it
is made by glass tube.
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23. Syringe
• The syringe works on the
existence of atmospheric
pressure.
• A syringe consists of a tight-
fitting piston which moves in a
cylinder, with a nozzle at one
end
• When the nozzle of
a syringe is dipped in a liquid
and its piston is withdrawn,
the pressure inside
the syringe is lower.
• The greater atmospheric
pressure acting on the surface
of the liquid pushes the liquid
up into the syringe.
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24. Water pump
• A lift pump is used to pump
water out of a well or to a
higher level. The greatest
height to which the water can
be pumped is 10 m. This is
equivalent to the atmospheric
pressure.
• Upstroke: When the plunger is
lifted, the upper valve closes
and the lower valve opens.
The atmospheric pressure,
acting on the surface of the
water, causes water to flow
past valve B into the cylinder.
• Downstroke: When the
plunger is pushed down, the
lower valve closes and the
upper valve opens. Water
flows above the plunger.
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25. Water Pump
• When the plunger is next
lifted, the upper valve closes
again and the lower valve
opens once more. the
atmospheric pressure, acting
on the surface of the water,
forces water past the lower
valve into the cylinder.
Simultaneously, the water
above the plunger is lifted and
flows out through the spout.
This process is repeated until
sufficient water is obtained.
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26. Air Pump
• In its most basic form, a bicycle
pump functions via a hand-
operated piston.
• During up-stroke, this piston
draws air through a one-way
valve into the pump from outside.
• During down-stroke, the piston
then displaces air from the pump
into the bicycle tire.
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