Simple Machines — Lever, Pulley, Inclined Plane, Wheel-Axle, Screw, Wedge

A simple machine is a device that changes the direction or magnitude of a force. There are six classical simple machines. PSC exams frequently ask about types of levers, mechanical advantage, and everyday examples.

Fundamental Concepts

Term	Formula	Meaning
Mechanical Advantage (MA)	MA = Load / Effort	How many times the machine multiplies force
Velocity Ratio (VR)	VR = Distance moved by effort / Distance moved by load	Ratio of distances moved
Efficiency	Efficiency = (MA / VR) x 100%	Percentage of useful work output
Ideal machine	MA = VR, Efficiency = 100%	No friction (theoretical)

1. Lever

A lever is a rigid bar that rotates around a fixed point called the fulcrum.

Three Classes of Levers

Class	Arrangement	MA	Examples
Class 1	Fulcrum between Load and Effort	Can be greater than, equal to, or less than 1	See-saw, scissors, pliers, crowbar, beam balance
Class 2	Load between Fulcrum and Effort	Always greater than 1	Wheelbarrow, nutcracker, bottle opener, door (hinged)
Class 3	Effort between Fulcrum and Load	Always less than 1	Tweezers, fishing rod, human forearm, broom, stapler

Lever Formula

MA = Effort Arm / Load Arm

Where:

• Effort Arm = Distance from fulcrum to point of effort
• Load Arm = Distance from fulcrum to point of load

Key Points

• Class 2 levers are force multipliers (MA is always more than 1)
• Class 3 levers are speed multipliers (load moves faster than effort)
• The human forearm is a Class 3 lever (elbow = fulcrum, bicep = effort, hand = load)

2. Pulley

A pulley is a wheel with a grooved rim through which a rope or chain passes.

Type	MA	How It Works
Single Fixed Pulley	1	Changes direction of force only; no force multiplication
Single Movable Pulley	2	Load attached to pulley itself; effort = half the load
Block and Tackle (n pulleys)	n	Multiple pulleys combine; MA = number of rope segments supporting load

Pulley Formulas

System	MA	VR
Single fixed	1	1
Single movable	2	2
Combination (n ropes supporting load)	n	n

Example: A block-and-tackle with 4 rope segments supporting the load has MA = 4, so a 400 N load needs only 100 N effort (ignoring friction).

3. Inclined Plane

A ramp or slope that reduces the force needed to raise an object.

Formula	Expression
MA	MA = Length of slope / Height
VR	VR = L / h
Force required	F = (W x h) / L (where W = weight, h = height, L = length)

Key Point: A longer, gentler slope has a higher MA (less effort needed).

Examples: Ramp, staircase, flyover approach road, loading dock ramp

4. Wheel and Axle

A larger wheel attached to a smaller axle; both rotate together.

Formula	Expression
MA	MA = Radius of wheel / Radius of axle
VR	VR = R / r

Examples: Steering wheel, door knob, screwdriver, bicycle pedal-and-gear, windlass (well-wheel)

Key Point: The larger the wheel relative to the axle, the greater the mechanical advantage.

5. Screw

A screw is essentially an inclined plane wrapped around a cylinder.

Formula	Expression
MA	MA = 2 x pi x R / Pitch
Pitch	Distance between consecutive threads
Lead	Distance screw advances in one full rotation

Examples: Screw jack, bolt and nut, corkscrew, drill bit, Archimedes screw (water lifting)

Key Point: Smaller pitch = greater MA = more turns needed but less effort per turn.

6. Wedge

A wedge is a double inclined plane that converts a force applied to its blunt end into forces perpendicular to its inclined surfaces.

Property	Detail
MA	MA = Length of slope / Width of wedge
Thinner wedge	Greater MA
Use	Splitting, cutting, holding

Examples: Axe, knife, chisel, nail, plough, teeth (incisors), doorstop, zipper

Comparison Table of All Six Simple Machines

Machine	Changes	Force Multiplied?	Direction Changed?	Common Example
Lever	Force magnitude and direction	Depends on class	Yes (Class 1)	See-saw
Pulley	Force direction (fixed) or magnitude (movable)	Movable: Yes	Fixed: Yes	Flagpole, crane
Inclined Plane	Force magnitude	Yes (always)	No	Ramp
Wheel and Axle	Force magnitude	Yes	No	Steering wheel
Screw	Force magnitude	Yes (greatly)	Rotary to linear	Jack, bolt
Wedge	Force direction	Yes	Yes (splits force)	Axe, knife

Efficiency in Real Machines

Machine	Typical Efficiency	Why Less Than 100%
Lever	90–98%	Friction at fulcrum
Pulley system	70–90%	Rope friction, pulley friction
Inclined plane	80–90%	Surface friction
Screw	25–50%	High thread friction (useful — self-locking)
Wedge	70–90%	Friction along surfaces

Frequently Asked PSC Questions

Q1. A pair of scissors is an example of which class of lever? Ans: Class 1 (fulcrum between load and effort)

Q2. The human forearm is an example of which class of lever? Ans: Class 3

Q3. What is the mechanical advantage of a single fixed pulley? Ans: 1 (it only changes direction, does not multiply force)

Q4. A screw is a modification of which simple machine? Ans: Inclined plane

Q5. If the effort arm of a lever is 60 cm and load arm is 20 cm, what is the MA? Ans: MA = 60/20 = 3

Q6. Which simple machine is a doorknob an example of? Ans: Wheel and axle

Q7. What is the formula for efficiency of a machine? Ans: Efficiency = (MA / VR) x 100%

Q8. A nutcracker is an example of which class of lever? Ans: Class 2 (load between fulcrum and effort)