Levers

INTRODUCTION

Archimedes once said, "Give me a place to stand and I can move the world." What he meant was that if he could stand far enough away from the earth he could use a lever to move it. Levers use distance to make heavy objects easier to move. The goal of this experiment is to demonstrate how a lever reduces the amount of force needed to move objects.

Lever

MATERIALS

VOCABULARY

Fulcrum: Point about which a lever turns or pivots
Effort arm: Distance from fulcrum to point where force is applied
Load arm: Distance from fulcrum to point where load is applied

WHAT TO DO

  1. Use the pencil as the fulcrum and the ½ yardstick as the lever. Use double sided tape to secure the pencil to a table.
  2. Use 5 washers as the load. Weigh the total number of washers that are used as the load. Place the load at the very end of the piece of wood. Place the dowel rod under the plank of wood at the center point (9" from one end). Measure the distance between the fulcrum and the load (i.e. How long is the load arm?).
  3. Place washers one by one on the opposite end of the lever. How many washers must be added to exactly balance or begin to tip the load washers on the other end? Weigh the washers that just balance the load.
  4. Remove the washers and move the fulcrum to 4 ½ inches from the load end of the lever.
  5. Place a five washer load on the lever and place washers one by one on the opposite end of the lever until the load is balanced or begins to tip. How many washers were used to balance the load? How much did they weigh?
  6. Remove the washers and move the fulcrum to 13 ½ inches from the load end of the lever.
  7. Place a five washer load on the lever and place washers one by one on the opposite end of the lever until the load is balanced or begins to tip. How many washers were used? How much did they weigh?

QUESTIONS

  1. Which position of the dowel rod required the least number of added washers to tip the load?
  2. Make a plot number of washers or total weight of washers used to balance the load versus distance between the fulcrum and the load for each measurement. Can you predict using this graph what weight of washers is required to lift the load washers if the fulcrum is placed 15" away from the load?

SUMMARY

Levers lift objects easiest when the fulcrum is as close to the load end as possible. There are four components of a lever system: 1) the lever (a bar or rod), 2) the fulcrum, 3) the load, and 4) the force used to balance the load.
There are three possible ways of ordering the load, fulcrum and the force, which corresponds to the three different classes of levers.
A first class lever has the fulcrum placed between the load and the balancing force. The balance that was studied in this experiment is a first class lever.
A second class lever has the load located in the middle and the fulcrum and the balancing force on opposite ends. Examples of second class levers: a wheelbarrow, hand truck, wrench, nutcracker, and the handle to a pencil sharpener.
A third class lever has the balancing force in the middle with the load and fulcrum on opposite ends. Commonly used third class levers include arms, legs, cranes, catapults, and fishing poles.

EXTENSION

  1. What class levers are: a hammer, a crowbar, a seesaw, and a ring pull top on a soda can?
  2. Draw a diagram of a lever system and label the four components.
  3. Design a toy using a lever in some part of the toy.

SOURCES

"Making Science Work: Forces and Machines." Terry Jennings, Raintree Steck-Vaughn Company, Austin, 1996. ISBN: 0-8172-3961-8.
"Investigate and Discover Forces and Machines." Robert Gardner, Julian Messner Press, Englewood Cliffs, 1991. ISBN: 0-671-69046-9.
"Starting with Science: Simple Machines." Deborah Hodge, Kids Can Press, Buffalo, 1998. ISBN: 1-55074-399-6.
"Simple Machines Made Simple." Ralph St. Andre, Teachers Ideas Press, 1993. ISBN: 1-56308-104-7.

Grade Level: This experiment is expected to be appropriate for grades 3 and above.

© S. Olesik, WOW Project, Ohio State University, 2001.

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