AIR FLOW JSS 3 (BASIC 9) BASIC TECHNOLOGY SECOND TERM WEEK 5

SECOND TERM: E-LEARNING NOTES

JS 3 (BASIC 9)

SUBJECT: BASIC TECHNOLOGY

WEEK: 5

TOPIC: AIR FLOW

CONTENT

• Air flow
• Bernoulli’s principle
• Aerodynamics

Air flow

This refers to air molecules in motion. Flow is an exclusive property of all fluids (liquids and gases). However unlike liquids, air does not necessarily need a channel or container for it to flow. Breeze/wind is formed when molecules of air are set in motion.Molecules of air can be set in motion by any of the following processes:

1. Blowing air
2. Using the bellows (often used by blacksmith)
3. Using pumps
4. Using fan

When liquids flow through channels, agents such as gravity or a mechanical device is necessary to sustain the flow. Liquid (water) flow could either be laminar (streamline) or turbulent.

In laminar flow, all the portions of the water move gently in a path parallel to the confining channel.

Turbulent flow is a force flow; water particles do not move in a straight line. An example of this is the water flow in drainage during a heavy downpour.

Moving air molecules possess energy. This energy can be applied in the following processes;

• Action of the wind mill

• Movement offlag attached to flag pole.
• Destructive action of the hurricane

When air moves over the surface of an object at high speed, the pressure on the surface is greatly reduced (i.e the faster air molecules move over a surface the lesser the pressure acting on the surface). This principle is called the Bernoulli’s principle. This principle is used for explaining the lift force experienced by helicopters and aeroplanes when they are in air. To demonstrate this principle, you may try blowing air between two papers; you’ll observe that the papers move toward each other instead of going apart. This is because increase in the speed of air between the papers result in decrease in the pressure between the papers.

A science that studies the force on object moving through air is called Aerodynamics.

Aeroplanes’ wings are designed to have a streamline shape which allows the air above it to move faster than the air under it. The pressure under the aeroplane is therefore greater than that above the aeroplane thereby resulting in net pressure acting under the aeroplane as well as a lift force on the plane. The streamline shape of the aircraft also minimises the frictional drag force opposing the motion of the plane.

[mediator_tech]

Aerofoil with a streamline shape

The drag force acts on the aeroplane in a direction perpendicular to the lift force. Summarily, four forces act on a body moving through air: L

1. The weight(W) of the body which act downward
2. The lift force(L) which act upwardTD
3. The drag force(D) which opposes the motion of the bodies
4. The thrust(T) of body itself moving it forwardW

Other applications of the Bernoulli’s principle include;

1. Balloon
2. Kite

Evaluation

1. state the Bernoulli’s principle
2. List the types of water flow.

SUB TOPIC 2: PNEUMATIC DEVICES

CONTENTS:

• Water wheel
• Turbines
• Air compressor
• Hydraulic lift
• Water sprinkler

Pneumatic devices.

These are devices that use compressed air to do useful work. Some of these devices also use liquids to transmit energy. They include:

1. Pumps and turbines
2. Air hammer
3. Compression pump
4. Garden sprinkler
5. Water wheel
6. Hydraulic jack
7. Paint sprayer

Water wheel

This is a simple mechanical device which converts water power into rotary motion. It is sometimes also called gravity wheel. Falling water is used to turn the axle of the water wheel.

water wheel

Turbines

This is a rotary machine which converts the energy of moving water, steam or hot gas into mechanical energy.

turbines

Air Compressor

Paint sprayer

Hydraulic lift

This applies the Pascal’s principle of transmissibility of pressure to generate a huge force by applying a small effort.

A small force can be used to lift a heavy car using the hydraulic lift. Many other hydraulic systems (e.g hydraulic press, hydraulic water pump, hydraulic jack…) also apply this principle.

Garden sprinkler

This applies the Newton’s third law of motion which states that for every action there is an equal but opposing reaction. When water is ejected from the nozzle of the sprinkler, the forward thrust of the water result in a backward push on the nozzle thereby making the sprinkler turn about it axis watering several portion of the garden and not just on a single spot.

Water sprinkler

EVALUATION

1. What are pneumatic devices?
2. Mention five types of pneumatic device.

Assignment

Students should consult their textbooks and make abrief note on the air hammer.