All About Levers

Experiment & Video

Levers, being simple machines, have only three simple parts. The load, the effort, and the fulcrum. Let’s start with the load. The load is basically what it is you’re trying to lift. The books in the last experiment where the load. Now for the effort. That’s you. In the last experiment, you were putting the force on the lever to lift the load. You were the effort. The effort is any kind of force used to lift the load. Last for the fulcrum. It is the pivot that the lever turns on. The fulcrum, as we’ll play with a bit more later, is the key to the effectiveness of the lever.

There are three types of levers. Their names are first-class, second-class and third-class. I love it when it’s that simple. Kind of like Dr. Seuss’s Thing One and Thing Two. The only difference between the three different levers is where the effort, load and fulcrum are.

A first-class lever is a lever in which the fulcrum is located in between the effort and the load. This is the lever that you think of whenever you think of levers. The lever you made in Experiment 1 is a first-class lever. Examples of first-class levers are the see-saw, a hammer (when it’s used to pull nails), scissors (take a look, it’s really a double lever!), and pliers (same as the scissors, a double lever).

The second-class lever is a little strange. In a second-class lever, the load is between the fulcrum and the effort. A good example of this, is a wheel-barrow. The wheel is the fulcrum, the load sits in the wheel-barrow bucket and the effort is you. Some more examples would be a door (the hinge is the fulcrum), a stapler, and a nut-cracker.

This fellow is the oddest of all. The third-class lever has the effort between the load and the fulcrum. Imagine the first-class lever, but this time the fulcrum is at one end of the board, the books are on the other end and you’re in the middle. Kind of a strange way to lift books huh? A few examples of this are tweezers, fishing rods (your elbow or wrist is the fulcrum), your jaw (the teeth crush the load which would be your hamburger), and your arm (the muscle connects between your elbow (fulcrum) and your load ( the rest of your arm or whatever you’re lifting)). Your skeletal and muscular system are, in fact, a series of levers!

What's Going On?

We’ve had a lot of fun levering this and levering that but now we have to get to the point of all this simple machine stuff. Work equals force times distance, right? Well, what have you been doing all this time with these levers? You’ve been moving something (the load) a distance against a force (gravity). You’ve been doing work. You’ve been exerting energy. See how it all ties in nicely?

In the experiment video, I wanted you to notice how much force you exerted and how much the load moved. You may have noticed that when the force was small (it was very easy to lift) the load moved a very small distance. On the other hand, when the force was large (hard to lift), the load moved a greater distance. Let me point your attention to one more thing and then we’ll play with this.

When the force used to lift the load was small, you moved the lever a large distance. When the force used to lift the load was great you moved the lever a small distance. Remember, work=force x distance. There is work done on both sides of the lever. The effort (you in this case) pushes the lever a distance against a force...work is done. The load also moves a distance against a force so there too...work is done.
Now it's your turn – go have fun!

Keep experimenting on your own. See you soon in the next issue!

Warmly,
Aurora