Applications of Pascal's Principle in Everyday Living

• Hydraulic systems can be used to obtain a large force by the application of a much smaller force.

A) Hydraulic Jack

Hydraulic jack

1) The pressure produced by the force applied is transmitted through the oil to the large piston. Thus the large piston is pushed up by a large force.

2) To lower the large piston, the release valve has to be opened to allow the oil to flow back into the reservoir.

B) Hydraulic Lift

Hydraulic lift

1) This pressure is transmitted through the oil to the large cylinder. Thus a force F2 which is strong enough to lift a heavy load such ad a car, is produced.

C) Hydraulic Brakes

Hydraulic brakes

1) Hydraulic brakes are used in vehicles to produce a breaking force on all the wheels simultaneously at the instant the break pedal is applied.

2) There are two types of brakes used in a car:-

• Disc brakes at the front wheels.
• Drum brakes at the back wheels.

3) At the front wheels, the small piston A exerts a force to push the brake shoes against two pieces of steel discs. Thus, the car is slowed down or stopped by the frictional force between the brake shoes and the steel discs.

Applications of Archimedes' Principle in Everyday Life

1) Ship

The ship

(a) The ship would sink to a certain level until its weight is equal to the buoyant force.

(b) To prevent this, a plimsoll line is marked on the hull of all ships to show the depths which are safe for them to navigate.

2) Submarine 

The submarine

(a) When afloat, water is driven out from the ballast tanks by compressed a larger buoyant force.

(b) The submarine can submerge to a depth where the buoyant to a depth where the buoyant force is equal to its weight.

3) Hot-air Balloons

(a) When the envelope of a balloon is filled with a gas of lower density than air such as hydrogen, helium or hot air, its weight decreases.

The total weight of the balloon = weight of the fabric + weight of the gas in the envelope.

(b) The balloon experiences a buoyant force = (volume of balloon) X (density of surrounding air) X g

The Hot-air balloons

(c) If the buoyant force is greater than the total weight of the balloon, it would be accelerated upwards by a net upwards force.

Hydrometer

Application of Bernoulli's Principle

A) An Aerofoil

1) An aerofoil is a curved wing used to produce a life (upwards force).

2) It is observed that the smoke lines are close together above the aerofoil where the air speed past the aerofoil is greather.

(a)

(b)

Aerofoil.

3) The pressure difference between the air below and above the aerofoil produces a resultant upwards force known as a lift.

4) When an airplane is moving horizontally, the weight of the airplane is balanced by the lift.

5) If the airplane is moving with constant speed, than

   (a) the lift = the weight

   (b) the thrust = the drag

Force on an airplane.

B) A Carburettor

A carburettor

1) Air flowing at a higher speed through the narrow section cause the air pressure there to become lower.

C) A Bunsen Burner

A Bunsen burner

1) When a Bunsen burner is connected to the gas supply, gas gusts out through the jet with high speed.

2) This creates a region where a low pressure exists around the jet.

D) An Insecticide Spray

1) When the piston is pushed into the cylinder, air gusts out at high speed through the narrow opening.

2) This produces a low pressure region around the opening.

An insecticide spray

3) The mixture of insecticide and air is then ejected as a spray of small droplets on insecticide.

Applications of Atmospheric Pressure

A) Drinking Straw

A drinking straw

1) When air is sucked out from a drinking straw, the air pressure inside become lower.
2) Then the higher atmospheric pressure acting an the surface of the drink pushes the drink into the drinking straw and enables it to be sucked into the mouth.


B) Syringe

A syringe

1) A syringe consists of a tight-fitting piston which moves in a cylinder, with a nozzle at one end.
2) When the nozzle is dipped into a liquid and the piston pulled up, the pressure below is reduced.
3) Then, the higher atmospheric pressure acting on the surface of the liquid pushes the liquid into the cylinder.

C) Siphon

Siphon

1) The rubber tube is filled with liquid and both ends of the tube are covered with the fingers.
2) When both ends of the tube are opened, liquid flowing out through Y creates a partial vacuum inside the tube.

D) Rubber Sucker

A rubber sucker

1) The rubber cup is made air tight by wetting its rim before pressing it against the wall to create a partial vacuum by driving the air out.
2) Then the higher atmospheric pressure acting in the outer surface of the cup presses it in position against the wall.

E) Vacuum Cleaner

A vacuum cleaner

1) When it is switched on, a fan sucks out a stream of air from the space X to create a partial vacuum.
2) The dust particles are trapped in a dust bag at X while the fast moving air is allowed to flow out from the back of the vacuum cleaner.

F) Lift Pump (Common Pump)

Lift pump

1) During the upstroke V1 closes and the pressure inside the barrel is reduced due to the increase in volume of the air inside it (Boyle's law)
2) The limitation of the lift pump is that it can to raise water up to a height of 10 m only since the atmospheric pressure cannot support a water column of height more than 10 m.

Applications of Atmospheric Pressure

A) Drinking Straw

A drinking straw

1) When air is sucked out from a drinking straw, the air pressure inside become lower.
2) Then the higher atmospheric pressure acting an the surface of the drink pushes the drink into the drinking straw and enables it to be sucked into the mouth.


B) Syringe

A syringe

1) A syringe consists of a tight-fitting piston which moves in a cylinder, with a nozzle at one end.
2) When the nozzle is dipped into a liquid and the piston pulled up, the pressure below is reduced.
3) Then, the higher atmospheric pressure acting on the surface of the liquid pushes the liquid into the cylinder.

C) Siphon

Siphon

1) The rubber tube is filled with liquid and both ends of the tube are covered with the fingers.
2) When both ends of the tube are opened, liquid flowing out through Y creates a partial vacuum inside the tube.

D) Rubber Sucker

A rubber sucker

1) The rubber cup is made air tight by wetting its rim before pressing it against the wall to create a partial vacuum by driving the air out.
2) Then the higher atmospheric pressure acting in the outer surface of the cup presses it in position against the wall.

E) Vacuum Cleaner

A vacuum cleaner

1) When it is switched on, a fan sucks out a stream of air from the space X to create a partial vacuum.
2) The dust particles are trapped in a dust bag at X while the fast moving air is allowed to flow out from the back of the vacuum cleaner.

F) Lift Pump (Common Pump)

Lift pump

1) During the upstroke V1 closes and the pressure inside the barrel is reduced due to the increase in volume of the air inside it (Boyle's law)
2) The limitation of the lift pump is that it can to raise water up to a height of 10 m only since the atmospheric pressure cannot support a water column of height more than 10 m.

Instruments for Measuring Atmospheric Pressure

A) Simple Mercury Barometer

Simple mercury barometer

1) It is completely filled with mercury. Any air bubbles inside are removed by inverting the tube several times and filling it again with mercury.
2) The tube is inverted into a dish of mercury with its open end well below the mercury level.
3) The space above the mercury column in the tube is a vacuum known as Torricellian vacuum.

B) Fortin Barometer 

Fortin Barometer

1) A Fortin barometer is an improved version of a simple mercury barometer. Its tube is enclosed in a metal case with glass windows at the upper part of the tube for viewing the mercury column.

C) Aneroid Barometer

Aneroid Barometer

1) An aneroid barometer is used more often than a mercury barometer because it contains on liquid and can be carried about conveniently.

2) Change in air pressure make the box contract or expand. The movements of the box are magnified by a system of levers which causes a pointer to move over a calibrated scale.

Instruments for Measuring Gas Pressure

A) Manometer

The Manometer

1) A manometer consists of a U-tube containing a liquid such as mercury or water. It is usually used for measuring differences in gas or liquid pressure.

2) A sphymomanometer is a mercury manometer designed for doctors to measure the blood pressure of patients. 

B) Bourdon Gauge

Bourdon Gauge

1) A Bourdon gauge is used for measuring very high pressure such as the pressure of steam in a boiler or the pressure of compressed gases.

2) This movement is magnified by the lever arrangement which turns the cog-wheel that moves the pointer over a scale to indicate the pressure reading.

Applying Bernoulli's Principle

Bernoulli's Principle.

(Bernoulli's principle story)

1) Bernoulli's Principle states that the pressure of a fluid (liquid or gas) decreases at the region where the speed of fluid flow increases.

Relationship between speed of fluid flow and cross-sectional area.

Volume of fluid                       = A1v1

entering per second

Volume of fluid                       = A2v2

leaving per second              

The fluid is incompressible, so

A2v2 = A1v1

v2 = A1

v1    A2

2) To increase the kinetic energy, force is required to do work while flowing through the narrow section of the pipe.

Applying Archimedes's Principle

Archimedes's Principle.

(The Story of Archimedes' Palimpsest 2000)

Idea on Buoyant Force.

A less dense object floats in water.

1) The density of a object is less than that water since it contains air, thus is floats. 

2) Similarly, a large iron ship that has large space filled with air floats due to its lower density while a small solid iron sinks in water due to its higher density.

Idea of buoyant force.

3) For the object to float, its weight is balanced by the buoyant force (upthrust) acting upwards. If the buoyant force is larger than its weight, it bobs up to maintain the force equilibrium.

Applications of Archimedes' Principle in Everyday Life.

1) Ship

The ship

(a) The ship would sink to a certain level until its weight is equal to the buoyant force.

(b) To prevent this, a plimsoll line is marked on the hull of all ships to show the depths which are safe for them to navigate.

2) Submarine 

The submarine

(a) When afloat, water is driven out from the ballast tanks by compressed a larger buoyant force.

(b) The submarine can submerge to a depth where the buoyant to a depth where the buoyant force is equal to its weight.

3) Hot-air Balloons

(a) When the envelope of a balloon is filled with a gas of lower density than air such as hydrogen, helium or hot air, its weight decreases.

The total weight of the balloon = weight of the fabric + weight of the gas in the envelope.

(b) The balloon experiences a buoyant force = (volume of balloon) X (density of surrounding air) X g

The Hot-air balloons

(c) If the buoyant force is greater than the total weight of the balloon, it would be accelerated upwards by a net upwards force.

Hydrometer

Applying Pascal's Principle

Pascal's Principle.

Idea of Transmission of Pressure in a Liquid.

1) Hydraulic systems work by using liquids which are under pressure.

2) The principle of transmission of pressure in liquid can be illustrated by using a piece of apparatus.

Pressure is transmitted uniformly through water.

(a) The bulb is immersed in water and the piston is raised slowly to draw in water.

(b) The bulb is removed from the water tank.

(c) Then the piston is pushed hard enough to apply sufficient pressure to the water.

(d) It will be observed that water squirts with equal force from all the holes on the bulb.

(e) The shows that pressure applied to a liquid will be transmitted uniformly throughout the liquid.

3) Since the volume of a liquid is constant, the pressure applied is transmitted equally in all directions throughout the liquid. This idea of the transmission of pressure in a liquid is stated clearly in the Pascal's principle.

Applications of Pressure in Liquids

A) Public Water Supply System.

Public water supply system

1) In a public water supply system, water from a river or a dam is pumped to a water treatment plant.

2) Due to gravitational pull, water in the storage tank is maintained at a high pressure and this enables water to flow to the houses of the consumers which are lower.

B) The Walls of a Dam

The side view of a dam

1) The walls of a dam increase in thickness downwards.

2) A thicker wall is required to withstand greater pressure since water pressure increases with depth.

C) Fire Hose Used by a Fire-fighter 

Fire-fighter using a fire hose

1) A fire-fighter requires a fire hose for directing a water jet of very high  pressure to put out fire in a high-rise building.

2) To produce a pressurised water jet, the water is accelerated by an electric pump before flowing through the fire hose.

D) Sphygmomanometer for Measuring Blood Pressure

A doctor taking a patient's blood pressure

1) A doctor using a special mercury-filled manometer called a sphygmomanometer to measure the blood pressure of a patient.

2) On releasing the air in the cuff slowly, the doctor taken the maximum blood pressure (systolic) reading at the instant he/she hears the first sound of a spurt of blood.

Liquid Pressure Increases with Density

Liquid pressure increases with depth.

1) Holes are made at different heights on the side of a tall vessel. These holes are fitted with side tubes which are plugged up and the vessel is filled with water.

2) This shows that liquid pressure increases with depth.