Machines — Part 1: Mechanical advantage, efficiency and levers: visual lesson, ICSE Class 10 Physics (Science Paper 1)

Lesson

Doing more with less

Part 1 — a machine lets a small effort move a large load, or a slow movement become a fast one. Every machine follows the same rules of work and energy.

In this lesson you will

Define load, effort, mechanical advantage, velocity ratio and efficiency
Derive efficiency = MA / VR and explain why MA < VR in practice
Classify levers and predict whether MA is more or less than 1
Identify levers in the human body

Table of four simple machines and how each helps
Machine	What it helps with
Crowbar	Lifting a heavy stone with a small effort
Tongs	Gripping quickly at a distance
Pulley on a well	Pulling down instead of lifting up
Wheelbarrow	Carrying a heavy load

Concept

Load, effort, MA and VR

A machine is a device by which a force applied at one point (effort, $E$ ) overcomes a force at another point (load, $L$ ). Mechanical advantage $\text{MA} = \dfrac{L}{E}$ (no unit). Velocity ratio $\text{VR} = \dfrac{d_E}{d_L} = \dfrac{\text{distance moved by effort}}{\text{distance moved by load}}$ (no unit). A machine can be a force multiplier (MA > 1), a speed multiplier (MA < 1, load moves farther or faster), or simply change the direction of the force.

Table defining load, effort, mechanical advantage and velocity ratio
Term	Definition	Unit
Load L	Force overcome by the machine	N
Effort E	Force applied to the machine	N
MA	L / E	None
VR	dE / dL	None

Concept

Efficiency and η = MA / VR

Work input $= E \times d_E$ ; work output $= L \times d_L$ . Efficiency $\eta = \dfrac{\text{output}}{\text{input}} = \dfrac{L\,d_L}{E\,d_E} = \dfrac{L}{E} \times \dfrac{d_L}{d_E} = \dfrac{\text{MA}}{\text{VR}}$ . In an ideal machine (no friction, weightless parts) $\eta = 1$ and MA = VR. In a practical machine some input is wasted against friction and in lifting moving parts, so output < input: $\eta < 1$ and MA < VR. VR depends only on the design; MA depends on friction and the load.

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