Levers, like all machines, can help us do work in three basic ways: 1) ... A lever is
a machine made up of a solid or rigid bar and a pivot point called a fulcrum.
LEVERS Introduction: Every day we see and use many kinds of levers. Today you may have used a pair of scissors to cut paper, or a broom to sweep the floor. Perhaps you pried open a can with a screwdriver, or took the cap off a bottle with a bottle opener. In each case you would have used a lever to help you do work. Levers, like all machines, can help us do work in three basic ways: 1) reducing the force you need to apply (multiplying your effort force), 2) reducing the distance and speed with which you need to move (multiplying your speed and distance), or 3) changing the direction of your force. For example: A car bumper jack reduces the force we need to apply (think of lifting the car by yourself!) and changes the direction of your force (as you push down the car goes up). A fishing rod multiplies your speed and distance. However a machine will never multiply force and multiply distance at the same time. It is possible that a machine will change direction of a force while doing one of these other two. A lever is a machine made up of a solid or rigid bar and a pivot point called a fulcrum. Although there are many different examples of levers in and around your home and school, they can be grouped into one of three types. The type or CLASS of lever depends on the location of the fulcrum, effort force, and the resistance force. The diagrams below illustrate the three classes of levers. In locating the fulcrum, effort force, and resistance force, the following symbols are commonly used: F = Fulcrum E = Effort force R = Resistance force E
R F
R F
First Class
R E
F
Second Class
E
Third Class
One method of remembering the lever class is to answer the question “WHAT’S IN THE MIDDLE?” The answer is 1-2-3 FRE. In other words, a 1st class lever has the Fulcrum in the middle, a 2nd class lever has the Resistance force in the middle, and a 3rd class lever has the Effort force in the middle. Knowing what lever class the lever is may also tell you what the lever will do for you (change direction, multiply force, or multiply speed & distance). Levers Lab PURPOSE: In this investigation you will: locate the resistance, effort, and fulcrum of various common levers. group levers into classes. After completing this investigation, you will be able to: list the three main purposes of a lever. identify the purpose or function of a specific lever.
PROCEDURES: PROCEDURE Part 1: Common Levers 1. Study the examples of levers shown on this page of this investigation. For each one, find and label on the appropriate line the following: the fulcrum (F), where you apply the effort force (E), and where the resistance is placed (R). 2. After locating the fulcrum, effort, and resistance for each lever pictured, identify each lever as either 1st, 2nd, or 3rd class on the line above the lever. The important point to remember is to determine which lever part is in the middle (1-2-3 FRE). Scissors = _____________class Board & Roller = _____________class
Nutcracker = _____________class
Paper cutter = _____________class
Baseball bat = _____________class
Bottle opener = ___________class
Ice Tongs = ___________class
PROCEDURES: PROCEDURE Part 2: Identifying le & lr 1. Study the examples of levers shown on this page of this investigation. For each one, find and label the braces representing the effort arm length (le) and the resistance arm length (lr). Remember … le is the distance between the fulcrum and the effort force lr is the distance between the fulcrum and the resistance force 2. On the line provided indicate whether the mechanical advantage of the lever is greater than (>), less than ( 1
MA ____ 1
lr MA ____ 1 MA ____ 1
MA ____ 1
MA ____ 1 MA ____ 1
Calculating Mechanical Advantage of a Lever Introduction: The distances de & dr with a lever are difficult. However, there is something else we can measure with exactly the same proportion – le (effort arm length) and lr (resistance arm length). These distances are measured from the fulcrum to where each of the respective forces are located – le = distance from fulcrum to effort force, lr = distance from fulcrum to resistance force. PROCEDURE Part 2: Calculating Mechanical Advantage of a Lever 1. Using a ruler measure the effort arm length (le) and resistance arm length (lr) of each of the levers listed in Data Table 1 and record them. 2. Calculate the mechanical advantage of each of these levers using the formula: MA = le/lr. This is the same formula as MA = de/dr. DATA TABLE 1 : Calculating MA of a lever Item
Effort arm length (le)
Resistance arm length (lr)
Mechanical Advantage (MA)
Bottle Opener Baseball Bat Tongs Scissors
QUESTIONS: 1. Which lever class has the fulcrum between the effort and resistance? 2. Which lever class has the effort between the fulcrum and resistance? 3. Would a hammer pulling a nail be in the same class as a hammer pounding a nail? Explain your answer.
4. Give an example of a lever other than the ones already so designated in this investigation that would be in different classes, depending on its use. 5. True or False: A lever that provides an easier effort force cannot, at the same time, also shorten your distance. 6. True or False: A lever that provides an easier effort force cannot, at the same time, also change direction. 7. True or False: A lever that shortens your distance can also change direction. 8. For the levers which you found provided an easier effort force, was the fulcrum closer to the effort or to the resistance, or were the distances equal? 9. For the levers which you found shortened your distance, was the fulcrum closer to the effort or to the resistance, or were the distances equal? 10. What is the relationship between lever class and mechanical advantage
