JS 3 (BASIC 9) BASIC TECHNOLOGY SECOND TERM WEEK 4

SECOND TERM: E-LEARNING NOTES

JS 3 (BASIC 9)

SUBJECT: BASIC TECHNOLOGY

WEEK 4

TOPIC MOTION

CONTENT:

• Motion
• Linear motion
• Rotary motion

MOTION

This can be defined as the change in position of objects. This is a common phenomenon in nature. The moon moves, we human move from one place to another… . It is also a common practice for various component of a mechanical system to move relatively to one another; examples include: the needle of a sewing machine at work, the tyre of a moving car etc

Mechanical systems are commonly engaged in basically TWO types of motion.

1. Linear motion
2. Rotary motion

Linear motion:

This can be defined as change in position in a straight line. Like the motion of the needle of the sewing machine or motion of a crane being hauled up using a pulley. There are different types/parts of a mechanical system that exhibit this type of motion. They include;

1. Lever: It helps us to do work easily. Examples are the crowbar, the door knob etc. It often has a pivot (or a point of support) about which the lever turns. This point is called fulcrum.An example is a crowbar.
2. Linkages; this is an assembly of metallic bars in which each bar is connected to at least two other bars in an elbow/sliding joint. They are often used for converting linear motion to rotary motion and vice versa or for converting a linear motion to another linear motion but in the opposite direction.Application of linkage include, bicycle brake, crank and slide

Bicycle brake

Linkages

Rotary motion:

This can be defined as change in position around fixed axis.Like the motion of the blade of a ceiling fan or the tyre of a moving car. There are two types of rotary motion:

1. One way rotary motion: This allows continuous rotation and can only be brought to rest by the application of a brake.Examples include the clock mechanism, the circular mechanical saws for cutting wood, shaft of cars… .

Note that in some of these motions, reversibility may be required ( e.g shaft of a moving car, trains or crane) while for others reversibility may be dangerous and need to be prohibited (e.g circular saw for cutting wood, clock mechanism) and their motions can be controlled by the ratchet wheel

ratchet wheel

N

1. Non return rotary motion: This allows intermittent rotation but only in one direction. i.e the motion can stop and continue at intervals in the same direction.

EVALUATION

1. State one difference between the one-way rotary motion and the non-return rotary motion.
2. Mention three mechanical systems in linear motion.
3. List some applications of the linkage system.

Sub topic 2

• Control of rotary motion
• Conversion of rotary to linear motion

Control of rotary motion

[mediator_tech]

Thisinvolves the use of devices for initiating and arresting the flow of motion. These devices include;

1. Brakes
2. Clutch
3. Ratchet

Brakes; These are devices used to slow down or bring to a complete stop a moving body. Brakes are used for removing kinetic energy form moving bodies. There are different types of brakes

1. Disc brake; used for light vehicles
2. Drum brakes; used for heavy vehicles
3. External block brakes; used for cranes and winches
4. Internal shoe brake; used for motorcycles and other small automobiles.

Disc brake

bicycle brake

Clutches;these are devices used for connecting and disconnecting two moving parts. Types of clutches include;

1. Friction clutch
2. Dog clutch

Disengaged shafts

Engaged shaft

Conversion of rotary to linear motion.

The following devices are used in the conversion of rotary motion to linear motion and vice versa;

1. Rack and pinion (e.g kerosene stove, kerosene lantern)
2. Crank and slider
3. Bench vice
4. G-clamp
5. Screw jack
6. Connecting rod and piston (motorcycles)
7. Reverse linkage and the push – pull linkage

Ratchet

These are devices that transmit motion intermittently or allow motion only in one direction.

ratchet wheel

N

Evaluation

1. Which of these devices is used for removing the kinetic energy in moving bodies? (a) clutch (b) brake (c) linkage (d) ratchet
2. — is a type of motion along a straight line. (a) linear motion (b) rotary motion (c) random motion (d) relative motion
3. Which of these brakes is suitable for heavy vehicles? (a) internal shoe brake (b) disc brakes (c) drum brake system (d) external shoe brake.
4. — is applied in raising the oil wick of kerosene stove. (a) rack and pinion (b) cranks and piston (c) cranks and connecting rods (d) screw

ASSIGNMENT

[mediator_tech]

1. Making a list of three mechanism that applies the following
2. Rack and pinion
3. Crank and connecting rod (piston)

WEEKEND READING ASSIGNMENT

Read your Basic Technology textbook written by Olawehinmi and answer the following questions:

1. Write a short note on each of the following
2. Aerodynamics
3. Streamline bodies
4. Pneumatic