FORM 4: 3.8 FORMULA

PRESSURE

PRESSURE IN LIQUID

PASCAL’S PRINCIPLE

ARCHIMEDES’ PRINCIPLE

FORM 4: 3.7 MEANINGS

ITEM	MEANING
PRESSURE	Pressure is defined as normal force per unit surface area.
GAS PRESSURE	Gas pressure is the force exerted on a surface by gas molecules per unit area of the surface.
ATMOSPHERIC PRESSURE	The atmospheric pressure is the pressure exerted by the atmosphere on the surface of the Earth as well as all objects on the Earth.
PASCAL’S PRINCIPLE	Pascal’s principle states that pressure applied to an enclosed liquid is transmitted equally to every part of the liquid.
BUOYANT FORCE	The buoyant force is the upward force resulting from an object being wholly or partially immersed in a fluid.
ARCHIMEDES’ PRINCIPLE	Archimedes’ Principle states that when an object is wholly or partially immersed in a fluid, it experiences a buoyant force equal to the weight of the fluid displaced.
BERNOULLI’S PRINCIPLE	Bernoulli’s Principle states that when the speed of a fluid increases, the pressure of the fluid decreases and vice versa.

FORM 4: 3.6 UNDERSTANDING BERNOULLI'S PRINCIPLE

BERNOULLI’S PRINCIPLE

Bernoulli’s Principle states that when the speed of a fluid increases, the pressure of the fluid decreases and vice versa.

ACTIVITIES SHOWING BERNOULLI’S PRINCIPLE

APPLICATIONS OF BERNOULLI’S PRINCIPLE

FORM 4: 3.5 APPLYING ARCHIMEDES' PRINCIPLE

THE MEANING OF BUOYANT FORCE

The buoyant force is the upward force resulting from an object being wholly or partially immersed in a fluid.

RELATIONSHIP BETWEEN BUOYANT FORCE AND WEIGHT OF FLUID DISPLACED

Buoyant force = W₁ – W₂

Weight of fluid displaced = W₃

It is found that, buoyant force = weight of fluid displaced

ARCHIMEDES’ PRINCIPLE

Archimedes’ Principle states that when an object is wholly or partially immersed in a fluid, it experiences a buoyant force equal to the weight of the fluid displaced.

APPLICATIONS OF ARCHIMEDES’ PRINCIPLE

§          When a submarine is diving into the sea, the valves of the ballast tank open to allow water to enter.

§          Thus, its overall weight is bigger than the buoyant force, allowing it to dive.

§          When a submarine rises to the surface of the sea, the ballast tank is pumped with compressed air and water is forced out of the tank through the open valves.

§         Thus, its overall weight is smaller than the buoyant force, allowing it to rise to the surface. 

§         Hydrometer is used to determine the relative density of liquids.

§         The upthrust of the liquid causes the hydrometer to float.

§         The higher the density of the liquid, the bigger the upthrust will be. Thus, the scale of the hydrometer increases in a downward direction.

§         Big bulb enables hydrometer to float.

§         Small bulb filled with lead enables the hydrometer to float vertically.

§        Thin stem of hydrometer increases the sensitivity.

§         Prior to departure, the air inside the balloon is heated by the gas flame to a temperature above 00 ^oC.

§         The air inside the balloon expands and part of it out of balloon through the hole below it.

§         Thus, the total weight of the balloon decreases.

§         If the total weight of the balloon is smaller than the buoyant force, it would be accelerated upwards.

§         Ships are marked with the Plimsoll line for safety purposes.

§         Due to different temperatures and salinity concentrations, the density of sea water at different parts of the world varies.

§         The Plimsoll line will help navigators to determine the safety level that ships can lie in the water and still be safely loaded under different conditions.

FORM 4: 3.4 APPLYING PASCAL'S PRINCIPLE

PASCAL’S PRINCIPLE

Pascal’s principle states that pressure applied to an enclosed liquid is transmitted equally to every part of the liquid.

HYDRAULIC SYSTEMS

Pressure is transmitted uniformly throughout an enclosed liquid.

APPLICATIONS OF PASCAL’S PRINCIPLE

HYDRAULIC JACK

1.     When a small piston is pushed, valve A closes and valve B opens.

2.     Hydraulic oil is forced through valve B and raises the big piston.

3.     When the small piston is pulled up, valve B closes and valve A opens.

4.     Hydraulic oil is drawn from the reservoir into the space under the small piston.

5.     Continuous up and down movements of the small piston will cause the big piston to move up to lift the car.

6.     When the release valve is opened, the weight of the car will force the big piston downward, pushing the hydraulic oil into the reservoir. The car will be lowered to its original position.

HYDRAULIC BRAKE

1.     When the driver’s foot presses the brake pedal, the piston in the master cylinder exerts pressure on the brake fluid.

2.     This pressure is transmitted to the wheel cylinder of all wheels.

3.     The pressure causes the pistons to press the brake shoes against the wheels to slow down the car.

FORM 4: 3.3 UNDERSTANDING GAS PRESSURE AND ATMOSPHERIC PRESSURE

THE MEANING OF GAS PRESSURE

Gas pressure is the force exerted on a surface by gas molecules per unit area of the surface.

INSTRUMENTS FOR MEASURING GAS PRESSURE

THE MEANING OF ATMOSPHERIC PRESSURE

The atmospheric pressure is the pressure exerted by the atmosphere on the surface of the Earth as well as all objects on the Earth.

INSTRUMENTS FOR MEASURING GAS PRESSURE

APPLICATIONS OF ATMOSPHERIC PRESSURE

FORM 4: 3.2 UNDERSTANDING PRESSURE IN LIQUIDS

RELATIONSHIP BETWEEN DEPTH AND PRESSURE IN LIQUID

The pressure in liquid increases with depth.

RELATIONSHIP BETWEEN DENSITY AND PRESSURE IN LIQUID

A liquid with a higher density exerts a higher pressure.

RELATIONSHIP BETWEEN GRAVITATIONAL ACCELERATION AND PRESSURE IN LIQUID

Liquid pressure increases as the gravitational field strength increases.

PRESSURE IN LIQUIDS

APPLICATIONS OF PRESSURE IN LIQUIDS