Mechanisms and motion

Technology

Grade 9

Mechanisms and motion

Module 1

Mechanisms and motion

Introduction

What is a mechanism?

• In our everyday life we are surrounded by mechanisms. They help make our life easier in many ways. Most of the mechanisms you use are so familiar that you never think about them. Simple things like door handles, light switches, parts of a bicycle and a car are only a few examples. In the past, in old machines such as steam engines, the mechanisms were easy to see. Today they are hidden behind panels and covers. Mechanisms allow us to do simple things like switching on lights, running a bath and peddling up the hill easily on a bicycle. You will discover the uses of different mechanisms, as we look at them closer in this module.

Activity 1

• Make a list of items that you think are examples of mechanisms? Sketches and pictures of these items can also be included.

Mechanisms and Motion

• Mechanisms can be used to change the speed, direction or force required to do something. Mechanisms may be able to help you but they cannot do it on their own. They need energy and someone or something to operate them. The energy that is used by a machine is called the input. The result of this energy input is called the output. A mechanism such as a bicycle can be explained with the diagram below.

Activity 2

• Explain the advantages of sprockets and chains used in bicycles.

• Mechanisms are concerned with motion. There are four main types of motion. These can be illustrated by means of human body movements.

Activity 3

• Name the type of motion illustrated by the products. Use arrows to indicate the direction of the motion.Product

  

  Type of motion _________________Product

  

  Type of motion ___________________Product

  

  Type of motion ______________________Product

  

  Type of motion ________________

Types of mechanisms

Mechanisms are used in machinery. There are five types of mechanism:

1. Levers enable forces to be applied at precise points.
2. Pulleys change the direction and speed of a movement, and allow the transmission of power.
3. Gears transmit rotary motion and force.
4. Cams and cranks convert uniform input motion to non-uniform output motion.
5. Screws allow rotary motion to transmit a linear force.

Activity 4

• Answer the following questions based on the pictures A – F.

1. Name the mechanism in each of A - F.
2. Suggest a use for mechanism A.

1. In B, Axle 1 rotates at 10 rpm. How fast will axle 2 rotate?

1. To what use may mechanism C be put?

1. In D, if W rotates clockwise, how can you make V rotate anticlockwise?

1. Sketch a toy that could use mechanism F.

Assessment

Memorandum

ACTIVITY 1

• Learners could list any product that they regard as a mechanism. The aim of the activity is to help the learners to become aware of how many products actually are mechanisms. Discuss their examples in the classroom.

ACTIVITY 2

2.1 Greater forces can be transferred

2.2 Chains do not slip/slide

2.3 Chains can be unlinked to facilitate removal

ACTIVITY 3

• Door handle Oscillating (handle) and backwards and forwards-movement (reciprocating)
• Tap Rotating movement
• Air pump Oscillating
• Pair of scissors Oscillating

ACTIVITY 4

1. A – Crank(-handle)

B – Gears

C – Propeller/screw

D – Pulley

E – Linkage/linking

F – Cam

1. Tricycle
2. Three times slower (15/5 = 3)
3. Store air-tight/Keep things tightly stored
4. Twist the rubber ring to form an 8.
5. Any cam-driven toy