Simple Machines
A simple machine is a device that changes the direction or magnitude of a force. Simple machines are everywhere — in scissors, ramps, wheels, and doorknobs.
What is Work?
In science, work = force × distance. Work is done only when a force moves an object. Simple machines make work easier by allowing you to use less force over a greater distance.
The six simple machines are: Lever, Pulley, Wheel & Axle, Inclined Plane, Wedge, Screw.
Lever, Pulley, Wheel & Axle
| Machine | How it works | Examples |
|---|---|---|
| Lever | Rigid bar on a fulcrum; changes force direction | Seesaw, crowbar, scissors, baseball bat |
| Pulley | Rope over a wheel; changes force direction or reduces effort | Flagpole, window blinds, crane |
| Wheel & Axle | Large wheel turns a small axle; multiplies force | Doorknob, steering wheel, bicycle wheel |
Lever Classes
Class 1: fulcrum between effort and load (seesaw). Class 2: load between fulcrum and effort (wheelbarrow). Class 3: effort between fulcrum and load (tweezers).
Inclined Plane, Wedge, and Screw
| Machine | How it works | Examples |
|---|---|---|
| Inclined Plane | Flat sloping surface; reduces force needed to lift | Ramp, highway on-ramp, slide |
| Wedge | Two inclined planes back-to-back; splits or holds objects | Axe, knife, doorstop, chisel |
| Screw | Inclined plane wrapped around a cylinder; holds or lifts | Screw, jar lid, drill bit, bolt |
Compound machines combine two or more simple machines. A bicycle uses a wheel & axle, pulleys (gears), and a lever (brakes).
Quick Quiz
Test what you just learned. Choose the best answer for each question.