# Making Work Easier | Class 8 Science

#### CLASS 8 SCIENCE REVISION QUESTIONS

Last Updated: 01-03-2023

## Simple Machines

Everyday, we use simple machines to helps us carry out daily tasks. Can you name any simple machines you know? Here are examples:

A hammer is used to help drive nails into objects as well as remove them.

- A panga is used to cut objects such as trees.
- Others can be a pair of pliers, jembe, saw, wheelbarrow and more.

Tools should be properly maintained to:
• make them last longer
• prevent them from rusting
• avoid accidents
• enable them to work efficiently.
Some of the ways that tools can be maintained is by:
• repairing them when needed
• sharpening the cutting tools regularly
• cleaning them after use
• oiling them to prevent rust when storing them
• storing them properly

### Balancing Weights

When balancing (such as on a see-saw), the heavy load should move closer to the turning point or the lighter object should move farther away from the turning point. Look at the image below

## Movement, Motion and Force

- Movement is the change in position of an object caused by force.
- Force is defined as a push or a pull exerted on an object.
- Force is measured in newtons (N). It is named after Sir Isaac Newton.
- Force can:
1. start a stationary object
2. speed up a moving object
3. change direction of an object
4. slow down a moving object
5. stop a moving object
Please note: An object can be stopped or changed direction only if the force applied is more than the opposite force.

### Types of Forces

#### Gravitational Force (Gravity)

- It is a force that pulls objects towards the center of the earth such as a falling apple. It can also be defined as a force that pulls objects towards one another such as the sun and the earth.

#### Magnetic Force

- It exists in magnets.
- A magnet has both North (N) and South (S) poles
- Attracts magnetic materials such as iron (e.g iron nails, pangas and more).
- In magnetism, like poles repel while unlike poles attract. Consider the figure below:

#### Friction Force

- Friction is the force that opposes motion
- It acts on the opposite direction of a moving object.

- Enables us to Walk
- Enables vehicles to move
- Helps when lighting a match stick
- Makes writing easier

- Brings about ware and tear
- Makes work harder
- Produces unwanted heat

##### Ways to increase friction
- Friction can be increased by making the surface more rough e.g adding murram on road, adding treads on wheels, tires and shoes

##### Ways of reducing friction
• using a lubricant
• using rollers
• streamlining objects
• using ball bearings
• smoothing out surfaces

## Levers

- A lever is a simple machine used to life heavy objects.
- Any lever has three parts: load, effort and fulcrum/pivot/turning point
- All levers are classified as either: First class, second class or third class levers. This is determined by the arranged of the Load(L), Effort(E) and Fulcrum(F).

### First Class Levers

- Fulcrum is between the load and the effort e.g claw, hammer, pliers, see-saw

### Second Class Levers

- Load is between the fulcrum and the effort e.g wheelbarrow, nut cracker.

### Third Class Levers

- Effort is between the fulcrum and the effort e.g Fishing rod, human hand, spade.

## Inclined Planes

- An inclined plane is a slope
- It makes work easier by increasing the effort distance - The greater the effort distance, the lesser the effort.
- Examples of inclined planes are: Ladders, Staircase, Wedge, Screw, road winding up a hill, Ramp

- The picture above shows a staircase. This is an example of an inclined plane.
- The picture below shows another example of an inclined plane - a road winding up a hill.

The road above is found in South Central China, in the Zhangjiajie National Forest Park

## Single Fixed Pulley

- A pulley is characterized by a wheel with a rope.

- A pulley makes work easier by changing the direction of the force.The effort is applied towards gravity which is much easier.
- A flag is an example of a single fixed pulley.

### Characteristics of a Pulley

• Effort is applied towards gravity
• Effort applied is equal to the load
• Effort distance is equal to the load distance
• The pulley has no mechanical advantage

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Give more examples on levers

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I wish you could give more examples and detailed explanations