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Project Summary

Difficulty	2
Time required	Very Short (a day or less)
Prerequisites	Playground with a see-saw
Material Availability	Readily available
Cost	Very Low (under $20)
Safety	Be careful getting on and off the see-saw!

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Abstract

Objective

In 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.

Introduction

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, Concepts and Questions to Start Background Research

• lever
• fulcrum
• mass
• weight

Questions

• 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?

Bibliography

• Levers: Simple Machines
  http://www.enchantedlearning.com/physics/machines/Levers.shtml
• Classes of Levers:
  http://www.usoe.k12.ut.us/curr/science/sciber00/8th/machines/sciber/lever1.htm
• After you've finished your experiment, see if you can solve the puzzle on this page:
  http://www.fearofphysics.com/Seesaw/seesaw.html
• 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

• see-saw
• tape measure
• bathroom scale
• one adult
• two children of approximately the same weight

Experimental Procedure

1. 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.)
2. 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 below).
3. If one person moves closer to the fulcrum, what happens to the see-saw? Make a second data table like the example below for the see-saw when it is unbalanced. (Be sure to note which side of the see-saw is up.)
4. Have C1 and C2 get off the see-saw, and then repeat steps 2 and 3 four more times.
5. 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 (kg)	Mass on Right (kg)	Trial (#)	Distance: Fulcrum to Left Mass (m)	Distance: Fulcrum to Right Mass (m)	Average Distance: Left (m)	Average Distance: Right (m)	Distance × Mass: Left (kg×m)	Distance × Mass: Right (kg×m)
   (Mass of C1)	(Mass of C2)	1
   		2
   		3
   		4
   		5
   (Mass of A)	(Mass of C1)	1
   		2
   		3
   		4
   		5

Variations

• 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.

• For more science project ideas in this area of science, see Physics Project Ideas.

Credits

La Né Powers

Edited by Andrew Olson, Science Buddies.

Last edit date: 2006-01-12 16:54:14

Career Focus

If you like this project, you might enjoy exploring careers in Physics.

	Physicist Physicists have a big goal in mind—to understand the nature of the entire universe and everything in it! To reach that goal, they observe and measure natural events seen on Earth and in the universe, and then develop theories, using mathematics, to explain why those phenomena occur. Physicists take on the challenge of explaining events that happen on the grandest scale imaginable to those that happen at the level of the smallest atomic particles. Their theories are then applied to human-scale projects to bring people new technologies, like computers, lasers, and fusion energy.			Nuclear Monitoring Technician Nuclear technology is used to image the human body, destroy cancer cells, sterilize food and medical equipment, create pest or drought-resistant seeds, and to generate power for 1 in 5 U.S. homes and businesses. Nuclear monitoring technicians help to keep the people who work with nuclear technology and the environment safe from excessive radiation exposure. They use special instruments to measure and monitor the radiation levels of workers, work areas and equipment, and they are involved in decontaminating work areas to safe levels. They also educate workers on radiation safety.
	Nuclear Medicine Technologist Many traditional medical imaging methods, like X-rays, can take pictures of certain parts inside the body, but sometimes these methods are not sensitive enough to detect a problem, or a picture is not enough—the doctor needs to see how a part is functioning, not just how it looks. That’s where nuclear medicine comes in. It can be used to see, for example, if bone repair is going on in a certain area, how a kidney is functioning, how a stomach is emptying, or how blood is flowing into and out of a heart. It can also be used to treat certain diseases. Nuclear medicine technologists are the special healthcare workers who administer radioactive drugs, take images of the patient, and then process, analyze, and show the computer images to the doctor.			Forensic Science Technician Guilty or not guilty? The fate of the accused in court lies with the evidence gathered at the crime scene. The job of the forensic science technician is to gather evidence and use scientific principles and techniques to make sense of it. It can be a grueling and graphic job, but very rewarding. If you like the idea of using science to help deliver justice, then you should investigate this career.

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