OK, the title is click-bait. You don’t need to use chocolate chips in this lesson but they sure are fun. I have used pennies or even beans. You simply need small objects that are consistent in weight and don’t roll.
Age level: PreK – third grade
Science Standards: for space considerations, these are addressed at the end
Materials Needed: 12-inch or cm rulers, tape, chocolate chips (or lentils, pennies, metal nuts, beans)
Levers are simple machines. That means they use few or no moving parts and can be the basis of more complex machines. Levers have been used since antiquity to lift or balance objects. In this lesson we will study teeter-totters and their kin to understand how they can be used to lift heavy objects with little effort.
Identify the parts of the lever: lever arms and fulcrum. The position of the fulcrum is crucial. In the following drawing, the fulcrum is in the middle and two children of equal size balance each other. But what if one child is much larger than the other one? Or, a child wants to teeter-totter with her mother who weighs quite a bit more? In those cases, the small child might not be able to lift the larger person and the teeter-totter wouldn’t work. Think: How can this problem be solved? As students provide thoughts, ask them to draw their solutions on the board. Think about this question as you proceed through the lesson. Either the fulcrum must be moved, or the position of the people on the teeter arms must change (effectively changing the fulcrum) The teacher may or may not want to share the correct solution at this point.
Capturing student interest
Show photos of extraordinary levers at work, or levers that went awry. Or provide a discordant event (see “Fun with Students”, below)
In this lesson, we will create a teeter-totter from a ruler; then use it to lift objects of unequal weights.
Step 1: Tape a 6-sided pencil firmly to a table.
Step 2: Balance a ruler atop the pencil. You have created a potential lever. Where are the lever arms? Where is the fulcrum? The ruler is 12 inches long. Where should you place the ruler so it is balanced on the pencil?
Step 3: Only after the pencil is balanced (both ends off the table), give the students two chocolate chips. Place one chip on each end of the ruler-lever and rebalance it. Make sure the two ends are off the table. Ask students to note the length of each lever arm (6 inches and 6 inches)
Step 4: Only after the two chips are balanced, give the children an extra chip. Ask them how they can change things so that a single chip can balance (or lift) two chips. Tell them they must keep the chips on the end of the ruler (because you want to emphasize the position of the fulcrum and lengths of lever arms). The single chip should be on the “zero” end of the ruler for easier computation. Students should note the lengths of each lever arm.
Step 5: After students have discovered they can change the lengths of the lever arms, give them 3 more chips and ask them to balance a single chip against 5 chips. Remember to leave the single chip on the zero end and keep all chips as close as possible to the end of the rulers.
Assessment and Thinking
What did you do, to enable a single chip to lift 5 chips? (made that side longer). Point out that longer levers do more work than shorter levers. Another way of thinking: Pushing on the end of a lever provides more strength than pushing midway on the arm. Some manufactured levers are designed to remind you where to push.
Who can draw a teeter-totter correctly to enable Jane and her mom to use it?
How could you correct the situation of the poor donkey and his cart (above?) Lengthen the cart arms and put the donkey at the head.
Could an ant conceivably lift an elephant on a teeter-totter? How would you do it and why would it work?
Fun with students via a discordant event
Rigging the game. Before asking students to start the lesson, I make one of two rigged rulers:
- Use red and black poster paint to paint one ruler in two equal 6-inch segments. Paint a second ruler in the same colors but make one end longer – hopefully, not enough for students to notice on casual inspection. The line separating the two colors will be put on the fulcrum. Use the first ruler to demonstrate how to balance one chip against the other. Switch out the second ruler while distracting them. Then use a “super chip” from a special jar to lift more than one chip. Ask students to explain.
- Use a regular ruler to balance two chips. Then switch that ruler with an identical one that has a penny taped to the bottom. In one case, a chip balances another chip. In the second case, with everything apparently the same, one chip will simply not balance the other chip. Ask students to figure it out. Note that unscrupulous merchants have rigged scales this way in the past. With modern laws and computerized scales this normally wouldn’t be a problem today.
Etching of Assyrians and levers; Nineveh and Babylon – a narrative of a second expedition to Assyria during the years 1849, 1850, and 1851 by Sir Austen Henry Layard 1874
Donkey cart in Kabul; photographer known, google photos
Nail Clipper: Amazon.om
All other photos and drawings are owned and copyrighted by Camilla Barry, 2020
This lesson addresses many Next Generation core standards that carry through grade levels PreK – 12. Examples are (but not limited to):
Look for pattern and order in observations
Compare attributes of objects through measurement
Reason abstractly and quantitatively
Model with mathematics, Compare numbers
Use materials and tools to solve a specific problem
Plan and Conduct an Experiment
Recall and gather information to answer a question
A problem can be solved through engineering
Multiple solutions to a problem are possible and should be compared/analyzed