Simple Machines: Making Work Easier

Learning Objectives

Define work in the scientific sense.

Identify the six types of simple machines.

Explain how simple machines make work easier by changing the direction or magnitude of a force.

Provide real-world examples of each simple machine.

What is Work?

In science, work has a very specific meaning. Work is done only when a force (a push or a pull) causes an object to move a distance. If you push on a wall as hard as you can, but the wall doesn't move, you haven't done any scientific work!

Simple machines are devices that make work easier. They don't reduce the total amount of work you have to do, but they can change how you do it. They can:

1.Multiply your input force: This means you can apply a small force to move a heavy object.

2.Change the direction of the force: This means you can pull down to lift something up.

There are six classic simple machines, which are the building blocks for all more complicated machines.

1. Lever

A lever is a stiff bar that pivots around a fixed point called a fulcrum. By pushing down on one end of the lever (the effort), you can lift a load at the other end.

Examples: A see-saw, a crowbar, a bottle opener. The location of the fulcrum, effort, and load determines the class of the lever.

2. Wheel and Axle

This simple machine consists of a large wheel rigidly attached to a smaller rod, or axle. When you turn the wheel, the axle turns with it. It multiplies force: a small force applied to the large wheel creates a much larger force at the axle.

Examples: A doorknob, a steering wheel, the pedal crank on a bicycle.

3. Pulley

A pulley is a wheel on an axle or shaft that is designed to support movement and change of direction of a rope or cable.

A single fixed pulley changes the direction of the force (you pull down to lift the load up), but doesn't multiply the force.

A movable pulley or a system of multiple pulleys (a block and tackle) can multiply the force, making it much easier to lift heavy objects.

Examples: Flagpoles, window blinds, cranes.

4. Inclined Plane

An inclined plane is a flat, sloping surface. It's a ramp! It allows you to move an object to a higher elevation with less force than lifting it straight up, but you have to move it over a longer distance.

Examples: A wheelchair ramp, a slide, a sloping road.

5. Wedge

A wedge is a triangular-shaped tool that is a portable inclined plane. Instead of moving an object up a ramp, you force the ramp into an object to split, cut, or hold it.

Examples: An axe, a knife, a doorstop.

6. Screw

A screw is an inclined plane wrapped around a cylinder. It converts a rotational force (a torque) into a linear force. It can be used to hold things together or to lift objects.

Examples: A jar lid, a drill bit, a light bulb base.

Key Terms

**Work: The transfer of energy that occurs when a force is applied to an object and the object moves in the direction of the force.
**Simple Machine: A mechanical device that changes the direction or magnitude of a force. The six simple machines are the lever, wheel and axle, pulley, inclined plane, wedge, and screw.
**Lever: A rigid bar that pivots on a fixed point called a fulcrum.
**Pulley: A wheel with a groove that a rope or cable can run over to change the direction of a force or to lift a heavy object.
**Inclined Plane: A flat, sloping surface, or ramp, that reduces the amount of force needed to lift an object.