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Exploring how a rigid bar and a pivot point can lift heavy loads.
Could you lift a 2,000-pound car with just your own strength? With a long enough bar and the right pivot point, the laws of physics say yes!
A lever is a simple machine consisting of a rigid bar that rotates around a fixed point. This fixed point is called the fulcrum. To make the lever work, you apply a force called the effort to move an object known as the load. Imagine a seesaw at the park: the heavy board is the bar, the metal support in the middle is the fulcrum, you are the effort, and your friend on the other side is the load. By using these three parts together, humans have been able to move massive stones and build monuments for thousands of years.
Let's identify the parts in a simple desk experiment: 1. Place a marker on your desk to act as the fulcrum. 2. Lay a ruler across the marker so it balances. 3. Place a heavy eraser on one end of the ruler (the load). 4. Push down on the opposite end of the ruler (the effort). 5. Notice how the eraser moves upward as you push downward.
Quick Check
What is the name of the fixed point that a lever pivots or turns on?
Answer
The fulcrum.
Imagine a student sitting from the fulcrum. To lift them using only of effort force: 1. Identify the load () and its distance (). 2. Calculate the required distance for the effort: . 3. Solve for : . 4. By sitting away, the lighter student can lift the heavier one easily!
Quick Check
If you want to make it easier to lift a heavy rock, should you move the fulcrum closer to the rock or closer to your hands?
Answer
Closer to the rock (the load).
One of the most useful features of a First-Class Lever (where the fulcrum is in the middle) is that it changes the direction of the force. Usually, to lift something up, you have to pull up. But with a lever, you can push down to make the load go up. This allows you to use your own body weight to help do the work. Gravity pulls down on you, and the lever converts that downward pull into an upward lift on the other side. This is why a crowbar is so effective at pulling nails out of wood!
Suppose you need to lift a (Newton) crate using a long lever. 1. You place the fulcrum away from the crate. 2. This leaves for the effort arm. 3. Using the formula , we find the Effort needed is only . 4. You have traded of movement to lift a heavy weight with of the force usually required!
In a first-class lever, where is the fulcrum located?
If you use a lever to lift a heavy box and you push down with of force to lift a box, what has the lever done?
A lever allows you to move a load a further distance than the distance you move the effort arm.
Review Tomorrow
Tomorrow morning, try to name the three parts of a lever and draw a simple diagram of a seesaw labeling each part.
Practice Activity
Find a pair of scissors at home. Identify where the fulcrum is, where you apply the effort, and where the load (the paper) goes. Is it a first-class lever?