Give It a Lift with a Lever
IntroductionHave you ever wondered how ancient people could lift very heavy objects, such as large stones, to build pyramids? A lever is a simple machine that can help people do just this. It can also help make other kinds of physical work easier by giving the user a mechanical advantage.
Common examples of levers you might see around you are seesaws, scissors, wheelbarrows and even the your own jaw. Although all of these levers have the same functional parts, they vary in where the different components are located. How much effort does it take to lift a heavy load using a common type of lever?
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BackgroundSeesaws and scissors belong to a certain class of levers, called class 1. Class 1 levers usually have a beam that is rigid, long and thin, like a ruler. Between the two ends of the beam is the fulcrum, or pivot point, which is the point at which the beam can balance and move freely up and down around. On one end, the user places the load to be moved. On the other end, the user can apply effort, or a force, to try and move the load.
The way levers work is by multiplying the effort exerted by the user. Specifically, to lift and balance an object, the effort force the user applies multiplied by its distance to the fulcrum must equal the load force multiplied by its distance to the fulcrum. Consequently, the greater the distance between the effort force and the fulcrum, the heavier a load can be lifted with the same effort force.
Extra: What is the graphical relationship between the amount of pennies needed to lift the soap when it is at different distances from the pencil? You can try this activity again but test different distances and then make a line graph of your results, putting the distance on the y (vertical) axis and the number of pennies on the x (horizontal) axis. What does the graphical relationship look like?
Extra: What happens if the load is doubled? You can test this by trying this activity again, but this time use two soap bars. Is twice the number of pennies needed to lift two soap bars? What if three or four soap bars are used?
Observations and ResultsWere less than half the pennies needed to lift the soap when the bag was 12 centimeters from the pencil compared with when the bag was six centimeters from the pencil? Was less than half this amount needed to lift the soap when the bag was 18 centimeters from the pencil?
As the distance between the bag and the pencil increases, the number of pennies or other objects needed to lift the soap decreases. However, when the distance is doubled, such as when going from six to 12 centimeters, the number of pennies needed to lift the soap does not simply become half. To balance objects using a lever, the effort force (the pennies) multiplied by its distance from the fulcrum (the pencil) must equal the load force (the soap) multiplied by its distance from the fulcrum. Consequently, the force exerted by the pennies needed to lift the soap is equal to the force the soap exerts multiplied by the distance between the soap and the fulcrum, all divided by the distance between the pennies and the fulcrum.
More to Explore"No Tipping," from Scientific American
"Levers," from V. Ryan at Technologystudent.com
"Escape from Merlin's Maze," from CYBERCHASE Thirteen/WNET, Educational Broadcasting Corporation, New York
"Levers," from Petervaldivia
Give It a Lift with a Lever," from Science Buddies
Teisha Rowland, PhD, Science Buddies
Science Buddies |
Physics, lever, force, tools, mass
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