Simple Machines: Lever, Inclined Plane & Pulley

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  • 0:08 Simple Machines
  • 1:35 The Lever
  • 4:12 The Inclined Plane
  • 7:07 The Pulley
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Lesson Transcript
Instructor: Damien Howard

Damien has a master's degree in physics and has taught physics lab to college students.

Discover what a simple machine is and how it operates. Then learn about the mechanical advantages various simple machines such as levers, inclined planes and pulleys give us.

Simple Machines

People are always looking for ways to make work easier and more efficient. Often we do this by inventing tools and machines to assist us with our work. Some of the earliest of these inventions are known as simple machines. A simple machine is defined as a basic device that alters the magnitude and/or direction of a force.

Some examples of simple machines are levers, inclined planes and pulleys. These three simple machines all alter force in such a way that it makes it easier to move an object. You might not have noticed, but we use these simple machines all the time. Every time you sweep the floor with a broom you're using a type of lever. If you've ever had to load anything heavy into a truck, the loading ramp is an inclined plane. An elevator uses a pulley system to move up and down between floors. These are just a few examples of the simple machines that appear all over the place.

When we want to know exactly how effective a simple machine is we look at something called mechanical advantage. Mechanical advantage tells us the advantage gained by using the machine to transmit force. We can find mechanical advantage by looking at the ratio of the load force resisting movement to the effort force the operator puts into the simple machine.

  • MA = mechanical advantage
  • F = force

Exactly how we find the mechanical advantage depends on the type of simple machine being used. In this lesson, we'll look at how to find mechanical advantage for levers, inclined planes and pulleys.

The Lever

Levers are one of the most common types of simple machines we use. They are used everywhere, from door handles to dinner utensils, scissors, see-saws, crowbars and more. However, not every lever is created equally. There are three different classes of lever. To determine the class of lever we need to know where the effort force, load force and fulcrum are located on the lever. The fulcrum being the point at which the lever pivots.

In a first class lever the effort force and load force are on opposite ends of the lever, and the fulcrum is somewhere between them. Our example of a see-saw is a first class lever. It has a fulcrum in the center, and the child on the ground creates an effort force with his weight while the child at the other end in the air acts as the load force.

A second class lever instead has the fulcrum and effort force on opposite ends of the lever and the load force somewhere between them. A wheelbarrow would be a second class lever as the wheel is the fulcrum on one end, and you supply an effort force on the opposite end. The load force is in the center with what you are carrying in the wheelbarrow.

Similarly to a second class lever, a third class lever has the fulcrum and load force at opposite ends, and the effort force somewhere between them. Our broom is an example of a third class lever with the load force at the brush end and the fulcrum at the handle end. You apply the force to the broom somewhere in between the two ends depending on how you are holding it.

Even though there are three different kinds of levers, the formula for mechanical advantage is the same for each. We can find the mechanical advantage for a lever by looking at the work the lever does. The work the user inputs on the lever is equal to the work outputted by the lever, where work is a force multiplied by a displacement. The displacements in this case being the distance between the effort or load force and the fulcrum.

simple machine work equation

lever work equation expanded

lever work equation rearranged

  • d = distance

Remember, mechanical advantage is the load force divided by the effort force. So, this formula lets us write mechanical advantage out in terms of distance alone.

mechanical advantage of levers

As long as you know what type of lever you are using, measuring the distances proves to be a simple way to find the mechanical advantage.

The Inclined Plane

The inclined plane is one of the most basic of the simple machines. Whether you're looking at a loading ramp, a wheelchair access ramp or a traditional playground slide it can all be boiled down to right angle triangles.

Just like with the lever, we use work to find our formula for mechanical advantage of an inclined plane. The only difference is what distances we use. For the work input, we are looking at the slope of the ramp, and for the work output, we are looking at the height of the ramp.

simple machine work equation

inclined plane work equation expanded

inclined plane work equation rearranged

inclined plane mechanical advantage

  • s = slope
  • h = height

In terms of geometry we can also write this as MA = hypotenuse / opposite.

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