Walk This Way!

Would you believe that you carry around at least two second-class levers with you all the time? Your ankle is actually a lever, and it helps your little feet move your much larger body. The picture at right shows where the fulcrum, load and effort are located. Can you see how these match up with the picture from yesterday's post?

Stand up, and pay attention to how your weight feels on your feet (this will work best if you don't have shoes on). You probably feel the weight more or less equally below your toes (the ball of your foot) and on your heel. Now lift up your heel so that you're on tiptoes. Go up and down a few times. When your heel isn't on the ground, all of the weight rests on the ball of your foot. You make an effort (green arrow) to lift your body (blue arrow) up, and the ball of your foot (red arrow) is the fulcrum, the point that doesn't move. Now just walk around, and concentrate on how your ankle works as a second-class lever.

So, had you ever realized that parts of your body are made up of simple machines?!?

Second-Class Levers

Levers of the second class have the fulcrum at one end, the load in the middle, and the effort exerted (up) at the other end, like the picture shown here. A good example of a second-class lever is a wheelbarrow. The wheel in front is the fulcrum. The load (whatever you are carrying) goes in the middle, and you lift the load by pulling up on the handles.

Have you ever given a friend a ride in a wheelbarrow? You probably couldn't lift him or her and carry him all around the yard, but it's easy to do with the right equipment!

First-Class Levers

Levers of the first class are levers in which the fulcrum is located between the load and where the effort is placed. A familiar example is a playground seesaw. The bar that the board rests on is the fulcrum (shown by the red triangle). A child sitting on one side of the seesaw (the blue rectangle) would be the load, and the effort would be measured by how hard it is to push down on the other side to raise the child (at the green arrow). Can you see you the fulcrum is between the load and effort?

Levers are useful because they let us lift heavy objects. You might be able to pick up the child with your arms, if he or she is small enough, but it will be much easier to lift the kid using the seesaw as a lever. What would happen if an adult climbed onto the seesaw instead of the child? Would the effort needed to lift the adult be greater or less? Even though it would be harder to lift the adult than the child, it is still easier to lift the adult with the lever than it would be to lift him or her without!

Here are a couple of free computer games based on first-class levers. (You'll have to watch a short ad first). Give them a try!

Seesaw Logic
Seesaw Ninjas

Heavy Lifting

The ancient Greek scientist Archimedes was the first person to correctly describe a lever mathematically. He supposedly said, "Give me a place to stand, and I shall move the earth with a lever." Well, that's an exaggeration because it would have to be one pretty big lever!

However, levers can be used to move heavy objects or to make a distant object move faster or farther. Here are just a few devices that use the principle of the lever to work: scissors, seesaws, tweezers, wheelbarrows, nutcrackers, the human jaw, fishing rods, and catapults. These things may not seem to have much in common, but you'll learn that they do.

There are two main parts to a lever. First, there is a bar or a board. This rests on a turning point called the fulcrum. The object to be lifted or moved is the load, and the work that you (or something else) does is called the effort.

There are three classes of levers: first, second, and third (OK, the names aren't very original!). The differences among them are the positions of the fulcrum, load, and effort. We'll look at each of them in turn, and you'll see how each of them can make your life easier!