A moment is the turning effect of a force about a pivot. The moment equals the force multiplied by its perpendicular distance from the pivot.

State the principle of moments.

A body in equilibrium has its clockwise moments equal to its anticlockwise moments about any pivot. The body then does not rotate.

A 300 N load sits 0.4 m from a lever's fulcrum. What effort, applied 1.2 m from the fulcrum on the other side, will balance it?

An effort of 100 N balances the load. Effort = (300 × 0.4) ÷ 1.2 = 100 N.

Define mechanical advantage.

Mechanical advantage is the load divided by the effort. A value above 1 means a small effort moves a larger load.

Define velocity ratio.

Velocity ratio is the distance moved by the effort divided by the distance moved by the load. The value depends only on the geometry of the mechanism.

CCEA A-Level Technology and Design 8900

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Electronic Control SystemsOption A

Topic overview Control systems, feedback and electronics safety Resistors, Ohm's law and power ratings Capacitors and RC timing Potential dividers, sensors and comparators Switches, pull-up and pull-down resistors Output devices and LEDs Transistors, Darlington pairs and thyristors Logic gates, truth tables and flip-flops 555 monostable and astable timers

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Mechanical and Pneumatic ComponentsOption B

Topic overview Open and closed loop mechanical and pneumatic control Safe working with compressed air and mechanisms Levers, linkages and moments Gear types and gear trains Pulleys, belts, chains and shaft fixings Cams, cranks and converting motion Compressed air supply and pneumatic valves Cylinders, shuttle valves, restrictors and reservoirs Pneumatic circuits for logic, timing and speed control

Mechanical and Pneumatic SystemsOption B

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Mechanical and Pneumatic Components

Levers, linkages and moments

3 things to know
AS 1 Paper 2

Overview

Moments and the principle of moments, mechanical advantage, velocity ratio and efficiency with worked levers, the three classes of lever, bell cranks and parallel linkages.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Evaluation

Why does a third class lever have a mechanical advantage of less than 1?

Key term

What is a moment?

Numbers

A force of 200 N acts 0.6 m from a pivot. Calculate its moment.

Questions from this subtopic

Each one with the model answer underneath.

1
What is a moment?
Model answer
A moment is the turning effect of a force about a pivot. The moment equals the force multiplied by its perpendicular distance from the pivot.
2
A force of 200 N acts 0.6 m from a pivot. Calculate its moment.
Model answer
The moment is 120 N m. Moment = 200 N × 0.6 m = 120 N m.
3
State the principle of moments.
Model answer
A body in equilibrium has its clockwise moments equal to its anticlockwise moments about any pivot. The body then does not rotate.
4
A 300 N load sits 0.4 m from a lever's fulcrum. What effort, applied 1.2 m from the fulcrum on the other side, will balance it?
Model answer
An effort of 100 N balances the load. Effort = (300 × 0.4) ÷ 1.2 = 100 N.
5
Define mechanical advantage.
Model answer
Mechanical advantage is the load divided by the effort. A value above 1 means a small effort moves a larger load.
6
Define velocity ratio.
Model answer
Velocity ratio is the distance moved by the effort divided by the distance moved by the load. The value depends only on the geometry of the mechanism.

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