Lesson 14.2: Six simple machines have many uses

Lesson Focus

This lesson introduces the six simple machines, the building blocks for all mechanical devices. You will explore how they make work easier by changing force and distance.

Learning Objectives

• Identify the six types of simple machines and provide a real-world example for each one.
• Explain how a lever changes the size and direction of the force needed to move an object.
• Learn to calculate a machine's mechanical advantage using its input and output forces.

All complex machines are combinations of six simple machines: the lever, wheel and axle, pulley, inclined plane, wedge, and screw. These tools make work easier by changing the direction or multiplying the size of a force. Think about how a shovel (a lever) helps you dig. Which simple machine is a doorknob?

A lever is a bar that pivots on a fixed point called a fulcrum. Applying an input force to the bar generates an output force to move a load. The positions of the fulcrum, input, and output create three lever classes, each changing force differently. Can you identify the fulcrum on a wheelbarrow?

A wheel and axle acts like a rotating lever; applying force to the larger wheel makes turning the smaller axle easier. A pulley, a grooved wheel with a rope, redirects force. A fixed pulley changes force direction, while a movable pulley multiplies force. How do both use rotation to help?

An inclined plane is a flat, sloping surface that reduces the force needed to lift an object by increasing the distance traveled. A wedge is a moving inclined plane for splitting, and a screw is an inclined plane wrapped around a cylinder for fastening. Why is a sharper knife (a thin wedge) better at cutting?

The Mechanical Advantage (MA) measures a machine's force-multiplying power, calculated with MA = Fout / Fin. For a perfect system without friction, the Ideal Mechanical Advantage (IMA) compares distances instead of forces. If a ramp's MA is 3, how many times does it multiply your force to lift an object?