Balancing the Load: The See-Saw as a Simple Machine
AbstractHave you ever tried to pull out a nail out of wood with your bare hands? Or have you tried to shove a staple through a stack of papers without a stapler? A hammer's claw, a stapler, a pair of pliers and a shovel are each examples of everyday tools that use levers to make our work easier.
Edited by Andrew Olson, Science Buddies.
ObjectiveIn this experiment, you will use a playground see-saw to investigate how a simple machine works. The objective is to learn the relationship between mass and distance when the see-saw is balanced and unbalanced.
The see-saw is not just a playground toy, it is an example of a simple machine.
In physics, simple machines are tools that make it easier to do work. A lever is an example of a simple machine. A lever is a straight rod or board that pivots on a stationary point called a pivot point or a fulcrum. Levers are often used to lift heavy loads. A see-saw, a shovel, and a wheelbarrow are all examples of levers.
Terms and Concepts
- What are the three classes of levers? Give an example of each.
- What are some common tools or simple machines that are examples of levers?
- Levers: Simple Machines
- After you've finished your experiment, see if you can solve the puzzle on this page:
- Introduction to General Physics Concepts:
Hewitt, Paul G. 2002. "Conceptual Physics," Prentice Hall, IL.
- Simple Physics Concepts for Kids:
Keller, R.W. 2005. "Real Science for Kids: Physics, Level 1," Gravitas Publications, Inc., NM.
Materials and Equipment
- tape measure
- bathroom scale
- one adult
- two children of approximately the same weight
- Determine the mass of each of the people participating in the experiment using the scale. (If your scale is calibrated only in pounds, you can convert to kilograms by multiplying by 0.454 kg/lb.) Record the mass of each participant in lab notebook. (For this sample procedure, we will refer to the participants using the following code: Adult=A, First child=C1, Second child=C2.)
- Have C1 and C2 sit on the see-saw. Have C1 and C2 adjust their positions until the two masses are balanced. Measure the distance of each mass from the fulcrum. (Note: The distance should be measured along the side of the lever from the center line of the fulcrum to the center line of each mass. If your tape measure is calibrated only in inches, you can convert to meters by multiplying by 0.0254 m/in.) Record the data in your lab notebook (see the example data table).
- If one person moves closer to the fulcrum, what happens to the see-saw? Make a second data table like the example for the see-saw when it is unbalanced. (Be sure to note which side of the see-saw is up.)
- Have C1 and C2 get off the see-saw, and then repeat steps 2 and 3 four more times.
- Repeat the experiment (steps 2–4), but this time try to balance A and C1 or A and C2.
Sample Data Table: Level Balanced Mass on Left
Mass on Right
Fulcrum to Left Mass
Fulcrum to Right Mass
Average Distance: Left
Average Distance: Right
Distance × Mass:
Distance × Mass:
(Mass of C1) (Mass of C2) 1 2 3 4 5 (Mass of A) (Mass of C1) 1 2 3 4 5
Ask an Expert
- After filling out your data tables, can you predict where you could have C1 and C2 sit on one side of the see-saw in order to balance A on the other side?
- Build a lever that has a moveable pivot point. What are the results of this experiment if you move the pivot point instead of the masses?
- With a mass on one end of the see-saw, push down on the other end. Experiment with how this type of lever could be used to lift and move a large mass.
If you like this project, you might enjoy exploring these related careers: