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Categorizing levers based on the arrangement of the fulcrum, load, and effort.
How could a small 6th grader lift a heavy car? It sounds like a superhero power, but with the right lever, it's actually simple physics!
Every lever in the world, from a tiny pair of tweezers to a giant crane, is made of the same three parts. First, there is the Fulcrum (), which is the pivot point where the lever rotates. Second, there is the Load (), which is the object you are trying to move. Finally, there is the Effort (), which is the force you apply to the lever. The way we categorize levers depends entirely on which of these three parts is sitting in the middle! To remember this, we use the FLE 1-2-3 rule: if the Fulcrum is in the middle, it is 1st class; if the Load is in the middle, it is 2nd class; and if the Effort is in the middle, it is 3rd class.
Quick Check
If you are using a tool and the object you are moving (the Load) is in the very middle, what class of lever are you using?
Answer
A second-class lever.
Imagine two friends on a seesaw. 1. The center pivot point is the Fulcrum. 2. Friend A (the Load) weighs . 3. Friend B (the Effort) pushes down on the other side. 4. Because the Fulcrum is in the middle, Friend B only needs to apply a force equal to to balance the seesaw.
In a second-class lever, the Load is in the middle (like a wheelbarrow). This design is the 'Powerhouse' because it always makes the load feel lighter. In a third-class lever, the Effort is in the middle (like a fishing rod or your own arm). While these actually require more effort to move a load, they are 'Speedsters.' They allow the load to move a much greater distance and at a higher speed than your hand moves. You use third-class levers whenever you need to reach far or move something quickly, like swinging a baseball bat!
You are moving of dirt in a wheelbarrow. 1. The wheel at the front is the Fulcrum. 2. The dirt in the bucket is the Load (in the middle). 3. You lift the handles at the back (Effort). 4. Because the Load is closer to the Fulcrum than your hands are, the load might only feel like to your muscles!
Quick Check
Why would anyone use a third-class lever if it requires more effort to lift the load?
Answer
Because third-class levers provide increased speed and distance for the load.
Your arm is a complex third-class lever! 1. Your elbow is the Fulcrum. 2. Your biceps muscle attaches just past the elbow to provide the Effort (in the middle). 3. The ball in your hand is the Load. 4. Even though your muscle pulls very hard over a short distance, the ball in your hand travels a huge distance very quickly!
Which part is in the middle of a first-class lever?
A nutcracker and a wheelbarrow are both examples of which class?
Third-class levers make it easier to lift heavy objects by reducing the force needed.
Review Tomorrow
Tomorrow morning, look at your arm while you pick up a toothbrush. Can you identify where the Fulcrum, Effort, and Load are?
Practice Activity
Go on a 'Lever Hunt' in your kitchen. Find one example of a pair of scissors (1st class), a bottle opener (2nd class), and a pair of tongs (3rd class).