MECHANICAL SYSTEMS

5.1 Introduction

When riding a bicycle, you apply some force to propel the bicycle. In practice, some systems have a set of physical components that convert input motion and force into a desired output motion and force. Such systems are called Mechanical systems or mechanisms.

These mechanisms are applied in machinery such as sewing machines, wheel chairs, wheelbarrows, etc. In this chapter, you will identify and model components/systems of simple machines.

5.2 Mechanisms

All mechanical devices and simple machines used today are made up o mechanisms. Mechanisms are made up of components.

Activity 5.1

Identifying common types of components used in mechanism

What you need: Photographs, exercise book and pens, school or home environment

What to do: Individually, carry out this activity.

Look at the photos in Figure 5.2, showing different types of components used in mechanical systems.

1. Identify them and tabulate their uses as shown below.
2. Which components are suitable for making a seesaw?
3. Which components can help you to draw water from a deep well?

Uses of Mechanisms

Activity 5.2 Identifying different components that make up mechanisms of a bicycle.

What you need: A bicycle, notebook, pen and pencil

What to do: In pairs, carry out this activity.

1. Identify the different parts and mechanisms used to assemble a bicycle.

2. Sketch the bicycle and label the parts.

5.3 Simple Machines

A simple machine is a device with few or no moving parts that are used to modify motion and force in order to perform work. Examples of simple machines include; inclined plane, lever, wedge, wheel and axle, pulley and screw.

Simple machines are assembled together using fastening devices.

5.4 Parts of Simple Machines

A simple machine is a mechanical system made up of different components. Each component plays a particular function in the machine.

Frames.

A frame is the main body to which all other components are fixed to make a system.

Activity 5.4 Exploring frames used in simple machines

What you need: A bicycle and a wheelbarrow, pen and notebook.

What to do: in pairs, carry out this activity.

1. Identify the two frames in Figure 5.6 and Figure 5.7. Relate them to the list of parts in the table below.
2. Examine the frames of a bicycle and a wheelbarrow. Relate them to the photographs/ illustrations below.
3. Identify the parts of the frames shown by arrows.
4. Copy and complete the following table. Indicate the uses of different parts of the frames of a bicycle and wheelbarrow respectively.
5. List the similarities between the frames.
6. Give at least three uses of each frame.

Shafts

Shafts play a big role in simple machines. They are responsible for the movements which eventually result in doing the required work.

A shaft is a cylindrical solid rod, where other parts or components like pulleys, gears, cranks and any other devices are fixed.

Axles

An axle is a rod passing through the centre of a wheel. A wheel or pulley rotates around it. Axles are used in simple moving machines or items. See examples application of an axle and their types in Figure 5.11 and Figure 5.12.

Activity 5.6 Identifying simple machines and items which use axles in your community

What you need: Home or school environment, pen and notebook

What to do: In groups, carry out this activity.

1. Using the drawing of axles above, illustrate the parts of the two axles.
2. Identify at least three simple machines and items in your community which use axles.
3. Sketch the items you have listed and state their uses in your environment.
4. Write a report and present to the class for comparison and getting feedback.

Conclusion: Axles are used in simple machines for doing work.

Pulleys

Pulleys play a big role in simple machines which solve our daily needs. They drive other machines through the belt mechanism. For instance, in pumping water, generating power, milling grains, etc. A pulley, therefore, is a wheel with a grooved rim used for transmitting rotary motion.

Uses of pulleys

Activity 5.7 Exploring uses of pulleys in your community

What you need: Home or school environment, notebook and pen

What to do: Individually, carry out this activity.

1. Identify the simple machines show in Figure 5.14.
2. Mention simple machines which use pulleys in your community.
3. State the functions of each of the machines.

Gears

Gears are used to transmit rotary motion and forces. They are efficient and can transmit great loads The most common type of gear is the spur gear. A gear is a toothed wheel Gears are also known as cogs. The main function of gears is to transmit rotary motion in moving machines such as a bicycle, a motorcycle, car, etc. Gears are also used for changing speed. There are several types of gears. Find out more about them.

Levers

A lever mechanism is used to simplify work. Levers can be used to do many of tasks, such as, lifting heavy loads, keeping doors open or closed. Have you ever pumped water from a bore hole? What do you think it uses? What about a knapsack sprayer? All those are examples of application of levers in your community.

Activity 5.8 Identifying different types of levers which are used in your environment

What you need: Home or school environment, notebook and pen

What to do: Individually, carry out this activity.

1. Identify three levers used at your home for opening or cutting different items/products Give two examples of each type

Wheels

A wheel is a component on a simple machine which enables the machine to move from one point to another effectively. Here are examples of simple machines using wheels.

Types of wheels

There are two main types of wheels, namely, solid wheels and inflatable wheels

Solid wheels :These are wheels with solid tyres made of plastic or rubber.

inflatable wheels: These have an inside tube but the exterior tyre is made of rubber and can be inflated or pumped.

Activity 5.9 Identifying types of wheels in your community

What you need: Home or school environment, pen and notebooks

What to do: In pairs, carry out this activity.

1. List the different simple machines which have wheels in your community.

2.Copy and complete the table below;

3. What type of tyres do you think:
4. a) an aeroplane uses?

b) a tractor uses?

Fastening devices

You will use fastening devices for holding or assembling components of simple machines together if you examine a simple machine like a bicycle you will see how they are used.

5.5 Modelling parts of a simple machine.

When modelling, select materials which look or behave like the real material

You can choose modelling materials from locally available materials and the specific material chosen will depend on the function of the model

Common modelling materials

These include:

plastic sheets, bags and form

• straws, rubber belts O cardboards of different thickness and colours
• manila paper O wood strips, plywood, dowels
• mouldable material like clay and plasticine
• joiners like adhesives, pins, clips, wires string, nails, cellotape and masking tape

Activity 5.10 Modelling components of a trolley for collecting vegetables from the school garden

What you need: Suitable modelling materials, cutting, measuring and marking-out tools and your school or home environment

What to do: In pairs, carry out this activity.

1. Select suitable modelling materials and use appropriate tools to maks components of a trolley. Model parts but do not assemble them. Belo is an example of a sketch of a trolley to guide you. Do not copy create your own design (Figure 5.20).
2. Your model trolley should have a provision of carrying vegetables