What Are Simple Machines?

Making Work Easier (Not Less)

In science, work means using a force to move something over a distance. Pushing a heavy box across the floor is work. Lifting a backpack onto a shelf is work. A simple machine is a basic device that makes work easier by changing the direction or amount of force you need to apply. Simple machines don't reduce the total amount of work — they just let you trade force for distance, or change the direction of your push or pull.

Scientists have identified six types of simple machines. Every complex machine — from bicycles to cranes to can openers — is built from combinations of these six.

1. Lever

A lever is a rigid bar that rotates around a fixed point called a fulcrum. When you push down on one end, the other end goes up. Seesaws, crowbars, and scissors are all levers. The farther you sit from the fulcrum on a seesaw, the less effort you need to lift someone on the other side — that's why a small kid sitting far out can balance a bigger kid sitting close to the middle.

2. Wheel and Axle

A wheel and axle is a circular wheel attached to a rod (the axle) that turn together. Doorknobs, steering wheels, and bicycle wheels all use this principle. The wheel gives you a larger surface to apply force to, which means you need less effort to turn the axle. Try opening a door by gripping the tiny axle instead of the knob — it's nearly impossible.

3. Pulley

A pulley is a wheel with a groove that holds a rope or cable. A single pulley changes the direction of force — you pull down on the rope, and the object goes up. Add more pulleys together in a block and tackle system, and you can multiply your force. Construction cranes use multiple pulleys to lift thousands of kilograms with relatively small motors.

4. Inclined Plane

An inclined plane is a flat surface tilted at an angle — a ramp. Instead of lifting a heavy box straight up onto a truck, you can push it up a ramp using less force over a longer distance. Wheelchair ramps, slides, and mountain roads are all inclined planes. The gentler the slope, the less force you need, but the longer the distance you travel.

5. Wedge

A wedge is really two inclined planes stuck together to form a sharp edge. Wedges are used to split things apart or hold things in place. Axes, knives, your front teeth, and even the bow of a ship are all wedges. When you push a wedge forward, it converts that forward force into a sideways force that pushes materials apart.

6. Screw

A screw is an inclined plane wrapped around a cylinder. Look at a screw closely — those spiral threads are just a ramp going around and around. Each turn of the screw moves it forward only a tiny amount, which means you can push something with enormous force using relatively little effort. Jar lids, spiral staircases, and drill bits are all screws.

Compound Machines

Most real-world tools combine multiple simple machines. A pair of scissors uses two levers joined at a fulcrum, with wedge-shaped blades. A bicycle combines wheels and axles, levers (the brake handles and pedals), pulleys (the chain system), and screws (the bolts holding it together). Once you learn to spot simple machines, you'll start seeing them everywhere.

Why This Matters

Simple machines are the building blocks of every mechanical device humans have ever created. The six simple machines — lever, wheel and axle, pulley, inclined plane, wedge, and screw — are combined in various ways to create everything from scissors (lever + wedge) to bicycles (wheel and axle + lever + pulley) to cars, cranes, and spacecraft. Understanding simple machines helps children see that even the most complex technology is built from basic principles of force and motion.

Simple machines also teach the fundamental physics concept that machines don't create energy — they redirect it. A ramp makes lifting easier not by reducing the work, but by spreading the same amount of work over a longer distance. This trade-off between force and distance is one of the most important ideas in physics and engineering.

Where Kids Get Stuck

The most common misconception is that simple machines reduce the amount of work. Children hear that a ramp "makes it easier" to lift a heavy box and assume less total work is being done. In reality, the same amount of work is performed — it just requires less force applied over a greater distance. This trade-off is the core principle of mechanical advantage, and it needs explicit demonstration.

Another difficulty is identifying simple machines in complex devices. Children can label a see-saw as a lever in a textbook, but they don't recognize the lever in a pair of scissors, a wheelbarrow, or a bottle opener. Hunting for hidden simple machines in everyday objects builds this recognition skill.

Students also confuse wedges with inclined planes. Both are triangular, but they function differently: an inclined plane stays still while an object moves along it (a ramp), while a wedge moves through a material (an axe splitting wood). The direction of motion relative to the triangular surface is the key distinction.

Try This at Home

• Simple machine hunt — Search your house for examples of each type: levers (door handles, light switches), wedges (knives, doorstops), screws (jar lids, bolts), pulleys (blinds, flagpoles), inclined planes (ramps, slides), wheels and axles (doorknobs, rolling pins).
• Ramp experiment — Use a board and a scale to measure the force needed to lift a heavy book straight up versus rolling it up a ramp. Same work, different force!
• Pulley play — Thread a rope over a broom handle balanced between two chairs. Attach a bucket and lift things. Compare the effort with and without the pulley.
• Build a Rube Goldberg machine — Chain together multiple simple machines so one action triggers the next. The crazier the chain, the better!

For more ideas, see our guide: Making Science Fair Projects Educational.

⚙️ Explore the Simple Machines Tool

Last reviewed: May 2026