Introduction:
Look at the see-saw at the top of the page. It is an example of a lever. A lever is a rigid rod or bar that pivots around a fixed point called a fulcrum. When you apply a force on one part of a lever, the lever pivots on the fulcrum and another part of the lever moves an object or person on the other part of the lever. In the picture above, see if you can locate the fulcrum.
In this activity you will make your own see-saw and experience the amount of force you will need to use to move a sack of potatoes up and and down as the distance from the fulcrum is changed.
There are three different types of levers.
- First class levers are ones in which the fulcrum is placed between the force and the object you want to move. Examples include pliers, scissors, shears, crowbars, etc.
- Second class levers are ones in which the object you want to move is placed between the force and the fulcrum. Examples include nutcrackers, screwdrivers, wheelbarrows, etc.
- Third class levers are ones in which the force is placed between the object you want to move and the fulcrum. Examples include your lower arm, tweezers, sugar tongs, etc.
Which type of lever is the teeter-totter shown above?
Materials:
- string (for tying a loop in the bag)
- long broom handle or wooden pole
- strong net bag
- potatoes or other objects for weights
- wooden rolling pin
- duct tape
- tall plastic waste paper basket
Classroom Management:
Students should build their own
levers in small groups or 3-5 students. If it is too difficult
to obtain the materials, one lever can be made for demonstration
to the entire class.
Activity Steps:
Design challenge : Making and Testing a First Class Lever.
- Tape the center of the broom handle (lever) to the rolling pin (fulcrum). Turn the waste paper basket upside down and place the rolling pin on it. Load one end of the broom handle with a bag of potatoes. Push down the other end to lift the potatoes. How does the amount of work you are applying compare to if you tried to lift the bag by itself? Draw a sketch of where the fulcrum, force, and object are on the lever.
- This time move your hands halfway toward the fulcrum. Leave the potatoes at the other end and push down. How does this compare to your first attempt to lift the potatoes with the lever? Can you notice a difference? Draw a sketch of where the pivot point, force, and object are on the lever.
- Finally, move the potatoes halfway toward the pivot point. Move your hands back to their original position at the end of the lever. Push down to lift the potatoes. How does this compare to your first two attempts to lift the potatoes? Draw a sketch of where the pivot point, force, and object are on the lever.
- Were there any levers in your neighborhood search for simple machines? How did they work? Were they all first class levers?
Extensions:
- Build and test different classes of levers with your waste paper basket and potatoes by moving the position of your rolling pin.
- Design challenge; build a boat with oars that get the greatest thrust.
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