Lifting with a Lever

Background Information for Teachers

A force is a push or a pull on an object. We exert forces every day, whether we are pulling open a door, pushing a child on a swing, or picking up a book. Sometimes we use machines to help us exert bigger forces. This is called mechanical advantage.

A lever is a type of simple machine that can be used to increase a force. A lever consists of a beam attached to a pivot (called the fulcrum). A lever allows you to take an input force (the effort) and amplify the output force (the load). A seesaw at the playground is a simple example of a lever. Imagine that you have three children who are all exactly the same weight. One of the children can lift the other two children on the seesaw by sitting twice as far away from the fulcrum (Figure 1).

Image Credit: Ben Finio, Science Buddies / Science Buddies

A seesaw is balanced on a fulcrum so that 2 meters of the board hang off each side. Three people of equal weight are able to balance on the seesaw if a person on one side of the seesaw stands at the furthest end and the other 2 people stand together 1 meter away from the end on the opposite side. Two people weigh twice as much as the single person but they are twice as close to the fulcrum so the forces exerted on both sides of the seesaw are the same.

Figure 1. A seesaw is an example of a lever.

You can make a miniature version of a seesaw using a pencil and a ruler. Place a pencil flat on a desk and put a ruler on top of it at the halfway point (the 6 inch mark). Place an object like a box of crayons on one end of the ruler, as shown in Figure 2. Then press down on the on the ruler just on the other side of the pencil (the 5 inch mark). How hard is it to lift the box? Try pressing down all the way at the end of the ruler instead (the 0 inch mark). It should be easier to lift the box. Now try moving the pencil closer to the box of crayons, and press down on the other end of the ruler again. It should be even easier to lift the box, because the effort (your finger pressing down on the ruler) is relatively much farther away from the fulcrum (the pencil) than the load (the box of crayons). In this lesson plan, your students will experiment with a similar setup to see if they can lift a heavy object off the floor with just one finger.

Image Credit: Ben Finio, Science Buddies / Science Buddies
Figure 2. A simple lever made from a ruler and pencil. The ruler is the beam and the pencil is the fulcrum. By pushing down on the far end of the ruler, you can lift the box of crayons.

There are other examples of levers all around us that might not be as obvious. Grab a pair of scissors— they are also a type of lever! Is it easier to cut through a piece of cardboard using the tip, or the part of the blade closer to the handle? If you cut with the part of the blade closer to the handle, the mechanical advantage is bigger (the force of you squeezing the handles is amplified more), so it is easier to cut. Now go try to open (or close) a door, first by pushing near the doorknob, and next by pushing near the hinges. You should notice that it is much harder to open (or close) the door by pushing close to the hinges.

Additional Background Links

• Simple Machines, Ducksters
• The Lever, eSchoolToday
• The Lever, Math and Science Activity Center

Prep Work (10 minutes)

• Gather supplies for each student.
• Print out copies of the student worksheet.
• Make sure your meter stick is stiff enough to lift a heavy object as described in the Explore section. If the meter stick bends significantly, you will need to use a lighter object as a weight or get a stiffer meter stick.

Engage (5 minutes)

1. Place book or other heavy object on the floor of the classroom.

   Does anyone think it is possible to lift this book off the floor with just one finger? Any ideas how?

   Students may express a range of ideas, including that they simply have enough strength to do it. Accept a few volunteers to try out their ideas.

2. Explain that today, their challenge will be to figure out how to use a simple machine to lift the object off the floor.

Explore (20 minutes)

1. Give each student a ruler, pencil, and box of crayons (or other object).
2. Ask the students to try to figure out how to use the items you have given them to lift the box of crayons with just one finger. Give them a few minutes to experiment.
3. After a few minutes, ask if anyone has found a solution to lift the box of crayons.
   1. If so, have them demonstrate their solution to the class.
   2. If not, prompt your students by asking them to think about a piece of playground equipment where one person can lift another (a seesaw). How could they make a seesaw with their ruler and pencil? Provide guidance or do a demonstration if your students cannot figure it out on their own.
   3. Explain that they have just built a lever, a type of simple machine. The seesaw on the playground is also a lever.
   Note: students are creative; they might think up some out-of-the-box solutions to lift the crayons! If so, congratulate them on their idea, and keep asking for more ideas until someone thinks of a lever.
4. Tell students to put the pencil down on their desk, place the ruler on top of it at the six-inch mark, and put the box of crayons on the end of the ruler toward the 12-inch mark (as shown in science background Figure 2).
5. Ask them to press down at the five-inch mark with one finger.

   Can you lift the box of crayons? How hard do you have to press down?

6. Challenge them to make it easier to lift the box of crayons (the box of crayons must remain at the same place on the ruler). The questions below will help devise a procedure as a class that they can follow to test their predictions.

   What can you change about your lever (what are the variables if we do an experiment)?

   If we cannot move the box of crayons, then we can change two things about our lever: we can move the pencil, and we can change where we press on the ruler.

   How can we change these variables one at a time? How can we determine if a change makes it easier or harder to lift the crayons?

   First, we can keep the pencil in the same place and change where we press on the ruler (the five-inch mark, the four-inch mark, etc.). Then, we can press in the same place (e.g. the zero-inch mark) while we move the pencil to different locations. Each time we make a change, we can see if it gets harder or easier to lift the box.

7. Have your students follow the procedure you agreed upon as a class in step 6 to test their levers.

   What changes make it easier to lift the box of crayons?

   Moving the pencil closer to the box of crayons, and pressing down farther away from the pencil, should both make it easier to lift the box. So, we can make it as easy as possible to lift the box by putting the pencil very close to the box, and pressing down all the way at the other end of the ruler.

8. Bring the class back together and show them the meter stick and marker.

   Does anyone have an idea for how we can lift this book off the ground with just one finger, using these materials?

   We can create a bigger version of our lever using the meter stick and marker. Place the marker on the floor, put the meter stick on top of the marker, and place the textbook on top of one end of the meter stick.

9. Challenge students again to see if anyone can lift the textbook with one finger.

   What did we learn from our experiments with the pencil and ruler? How can we make it as easy as possible to lift the textbook?

   We learned that two things made it easier to lift the box of crayons: moving the pencil closer to the box, and pushing down on the ruler farther away from the pencil. So, we can make it easier to lift the book by putting the marker closer to the book, and pressing down on the opposite end of the meter stick.

Reflect (5 minutes)

Remind your students that they just built a type of simple machine called a lever. The lever is made up of smaller parts (the ruler/meter stick and pencil/marker) that could not accomplish the task on their own. Optionally, you can draw a diagram of a lever on the board (or show the students Figure 1 from the science background) and go over the terms beam, fulcrum, effort, and load.

What variables did we change in our experiment?

We changed the location of the pencil (the fulcrum) and where we pressed down on the ruler (the effort).

How did we make it easier to lift the box (the load)?

We moved the pencil (fulcrum) closer to the box and pressed down (effort) farther away from the pencil.

Can anyone point out other examples of levers the classroom?

Examples of other levers in your classroom include (but are not limited to) scissors and doors. See the variations section for some quick demonstrations you can do with other types of levers.

Assess

1. Online quiz, assignable in any LMS
2. Quiz (pdf) and answer key (pdf)

Make Career Connections

Discussing or reading about these careers can help students make important connections between the in-class lesson and STEM job opportunities in the real world.

Mechanical Engineer

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Career Profile

Mechanical engineers design and build devices like cars, bikes, and airplanes that contain levers and many other types of simple machines like gears and pulleys. Read more

Lesson Plan Variations

• Many real-world objects that we use every day are actually levers. Here are a few examples you can use in your classroom:
  • Cutting cardboard with scissors. Is it easier to cut through the cardboard with the tip of the scissors, or the part of the blade closer to the pivot?
  • Opening and closing a door. Is it easier to push/pull on the doorknob, or very close to the hinges?
  • A seesaw. Can one student lift two students (or the teacher) by adjusting the distances they sit from the pivot?
• Using such standardized objects as weights (e.g. pennies or rubber erasers) and Equation 1 from the background section, have your students do an experiment where they predict how much effort force will be required to balance a load at a certain distance from the fulcrum. For example, you could ask, "If you put four pennies two inches from the fulcrum, how many pennies would you need to place four inches from the fulcrum to balance the lever?" (answer: two pennies). Note that it may be difficult to get the ruler to balance perfectly on a pencil—try using your finger instead.