Simple Machine – JSS3 Basic Science Lesson Note (Third Term)

A simple machine is a device that makes work easier by using a small effort at one point to overcome a load at another point.

Behavioural objectives

By the end of the lesson, students should be able to:

1. define a simple machine and give examples;
2. list the six types of simple machine;
3. name the three parts of a lever;
4. describe the three orders of lever and give an example of each;
5. state the uses of the wheel and axle, pulley, wedge, screw and inclined plane.

What is a simple machine?

A machine is a tool or device that makes work easier by using a force (effort) at one point to overcome a resisting force (load) at another point.

• Effort: the force we apply to the machine.
• Load: the resisting force or weight the machine moves.
• Examples of machines: a plier, the human arm, a gear and a pulley.

How do machines make work easier?

• Smaller effort: a small force can move a large load.
• Change of direction: a pulley lets us pull down to lift a load up.
• Convenience: a ramp makes it easier to move a drum onto a truck.

What is mechanical advantage?

Mechanical advantage (MA) is the number of times a machine multiplies the effort applied to it.

• Formula: MA = load ÷ effort.
• Unit: none, because it is a ratio of two forces.
• Example: a load of 200 N lifted with an effort of 50 N gives MA = 200 ÷ 50 = 4.

What are the types of simple machine?

There are six types of simple machine: lever, wheel and axle, pulley, wedge, inclined plane and screw.

What is a lever?

A lever is a stiff bar that rests on a pivot (the fulcrum), with a load at one point and an effort applied at another.

What are the parts of a lever?

A lever has three parts: the load, the effort and the fulcrum.

• Load: the point of the resisting force.
• Effort: the point where force is applied.
• Fulcrum: the turning point (pivot) of the lever.

What are the types of lever?

There are three orders (classes) of lever: first order, second order and third order.

• First order lever: the fulcrum is between the load and the effort (L F E). Examples: scissors, claw hammer, seesaw.
• Second order lever: the load is between the fulcrum and the effort (F L E). Examples: wheelbarrow, nutcracker, bottle opener.
• Third order lever: the effort is between the fulcrum and the load (F E L). Examples: forearm, tweezers, fishing rod.

What is a wheel and axle?

A wheel and axle is a simple machine made of a large wheel fixed to a smaller axle, both turning on the same axis.

• Effort position: the effort is usually applied to the large wheel.
• Effect: the axle turns with a larger force than the effort applied.
• Examples: bicycle, wagon, steering wheel, door knob and the winch over a well.

What are the uses of the wheel and axle?

• Drawing loads: it draws out heavy loads from depths, such as a bucket of water from a well.
• Turning effect: it creates the turning effect in a bicycle.

What is a pulley?

A pulley is a wheel with a groove over which a rope or chain runs, used to lift loads.

• Direction: it changes the direction of the pull.
• Combination: two or more pulleys working together reduce the force needed to lift a load.

What are the uses of the pulley?

• Cranes: it lifts and moves loads on building sites.
• Lifts (elevators): it helps raise and lower the lift car.

What is a wedge?

A wedge is a triangular tool that works as a portable inclined plane.

• Separating: it separates two objects or parts of an object.
• Lifting: it can lift an object.
• Holding: it can hold an object in place, as a door stop does.
• Examples: axe, knife, chisel and nail.

What is the use of the wedge?

• Splitting: it splits objects open, especially wood.

Cross-section of a splitting wedge with its length oriented vertically. Wedges are used to split things.

What is a screw?

A screw is a fastener with a helical ridge, called a thread, that winds round a central shaft.

• Direction: most screws tighten when turned clockwise, and a few tighten when turned anticlockwise.
• Examples: wood screw, bolt, bottle cap and the screw jack.

What is the use of the screw?

• Fastening: it holds objects firmly together when turned into wood or other hard materials.
• Lifting: a screw jack uses it to raise heavy loads such as a car.

What is an inclined plane?

An inclined plane is a flat surface tilted at an angle, with one end higher than the other.

• Raising or lowering: it helps raise or lower a load.
• Obstacles: it is often used to move a load over a vertical obstacle.
• Examples: a ramp, a sloping plank onto a truck and a staircase.

Evaluation

1. What is a machine?
2. List the six types of simple machine.
3. Name the three parts of a lever.
4. Give one example each of a first order, second order and third order lever.
5. State one use of a wedge.

Assignment

Describe the three orders of lever. For each order, state where the fulcrum, load and effort are placed and give one example.