Students use wood, wax paper and oil to investigate the importance of lubrication between materials and to understand the concept of friction. Using wax paper and oil placed between pieces of wood, the function of lubricants between materials is illustrated. Students extend their understanding of friction to bones and joints in the skeletal system and become aware of what engineers can do to help reduce friction in the human body as well as in machines.
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- Colorado: Science
- International Technology and Engineering Educators Association: Technology
- Next Generation Science Standards: Science
- Plan and conduct an investigation to provide evidence of the effects of balanced and unbalanced forces on the motion of an object. (Grade 3)  ...show
- Define and describe friction in everyday life.
- Relate friction to bones and joints in the human body.
- Explain what the human body and engineers do to reduce friction.
- Describe how the astronauts learn to work without friction in outer space.
- 1 wood block (small size)
- 1 wood board (at least longer than the wood block)
- 2-3 paper towels
- 1 square of waxed paper (enough to cover each of the wooden block and board)
- 2 copies of the Joint Worksheet
- Pictures of human joints
- Vegetable cooking oil
- Cellophane tape
|Ball and Socket:||A joint in which a ball moves within a socket (such as in the hip).|
|Cartilage:||A usually translucent somewhat elastic tissue.|
|Friction:||The force that resists relative motion between two bodies in contact.|
|Hinge joint:||A joint that only allows motion in one plane.|
|Synovial fluid:||A lubricating fluid secreted by your body.|
|Sliding joint:||A joint where the opposing surfaces are nearly planes; one that allows sliding or gliding motion.|
|Osteoarthritis:||A condition where the cartilage in joints wears away and allows bone to rub against bone, causing friction and, oftentimes, pain.|
|PABF (Precision Air-Bearing Facility):||A special floor that NASA uses to help astronauts learn how to work without friction; similar concept as an air hockey table.|
Before the Activity
- Gather all necessary materials.
- Obtain pictures of human joints from the library or internet (http://ovrt.nist.gov/projects/vrml/h-anim/jointInfo.html).
With the Students
- Discuss the following different kinds of joints and location in the body.
- Ball and socket joint: located in the hip and shoulder; connection between ball-shaped and cup-shaped bones. The ball can twist in many directions and is very flexible.
- Hinge joint: found in the elbow and knee; bones fit together so that movement in only one plane is possible. This is the least flexible joint.
- Sliding joint: located in the feet and hands; flat surfaces of bones slide over each other rather than rotating about an axis.
- Examine pictures of joints from library or internet resources. Have students draw an example of each joint on their Joint Worksheet.
- Have students rank the joints in terms of flexibility. Use " < " to show increasing flexibility (i.e., Hinge < Sliding < Ball and socket) or " > " to show decreasing flexibility (i.e., Ball and socket > Sliding > Hinge).
- Students should rub the wood block along the wood board. The students will feel friction. Define friction to the students as a force that resists motion.
- Ask students to give different examples of friction and list their responses on the board. (Possible answers: socks against carpet, brakes on the car, skateboard on pavement/concrete, tires on the road, etc.) Explain that joints would have friction if they rubbed against each other. Ask the students if they know what osteoarthritis is, and then explain how a person develops osteoarthritis. (Answer: Their cartilage wears away, and bone rubs against bone.)
- So how is friction reduced? Engineers use oil to create a barrier between two surfaces to reduce friction. The body uses cartilage and a fluid, called synovial fluid, to reduce friction in joints.
- Have the students wrap both wood surfaces with waxed paper and tape it down. Then have the students rub the surfaces together. What happens? (Answer: The wood slides more easily, friction is reduced.) The waxed paper acts like cartilage.
- Now add a little cooking oil to the waxed paper on the wood board (remind students to be careful, as the paper is slick and the oil will run very easily). Have the students rub the block along the board again. What happened? (Answer: Friction is reduced even further.) This represents the synovial fluid.
- Discuss with students how friction can wear down bones and joints over time. What could engineers do to help reduce friction in artificial limbs? (Answer: Engineers could develop fluids and surfaces to help reduce the friction in artificial bones and joints.)
- Engineers who work for NASA are figuring out the best ways to help the astronauts have healthy bones and joints while they travel in space. Have the students brainstorm ways to help astronauts move around in a frictionless environment.
- Have students push on a heavy object (such as the teacher's desk). Ask students what is balancing the force they exert on the desk. (Answer: Friction force balances the force they put on the desk.)
- Ask students what will happen if the force they exert on the desk becomes unbalanced with the friction force between the desk and the floor. (Answer: The desk will start moving.)
- Ask students to try to define friction. (Answer: The force that resists relative motion between two bodies in contact.) Have them give words that would describe friction. Write these words on the board. Work through the discussion with them until the class comes up with a good definition.
- Ask students if friction is a good thing or a bad thing; discuss as a class. (Answer: It is both good and bad! It is great for slowing things down, but it can also cause wear and tear in our bodies and in machines.)
- As a class, brainstorm ideas to reduce friction between the desk and the floor. Have students plan a way to reduce this friction. (One possible solution: Pour cooking oil on the floor beneath the desk.)
Activity Embedded Assessment
- Vocabulary terms to use: friction, synovial fluid, hinge joint, ball and socket joint, sliding joint, cartilage, osteoarthritis, PABF, lubrication.
- Ask students to predict what would happen if the force they exert on the desk and the friction forces become unbalanced by reducing the friction. (Answer: The desk will begin to slide.)
- For older students, discuss how friction over time affects the maintenance costs associated with a machine. (For example, friction on car tires wears down their treads, and they eventually need to be replaced.)
- For younger students, discuss friction as the rubbing of two objects. Have them complete the activity and discuss how friction in bones could be bad for the skeletal system.
Canright, Shelly. National Aeronautics and Space Administration, For Students (Grades 5-8), Features and News, "Astronauts in Training," May 27, 2004.
Jones, J.R. National Aeronautics and Space Administration, Langley Research Center, "NASA Space Vehicle Design Criteria: Lubrication, Friction, and Wear," NASA SP-8063, June 1971.
National Aeronautics and Space Administration, Space Operations Missions Directorate, NASAExplores, Express Lessons and Online Resources, "Two-Ton Hockey Pucks," November 12, 2003. http://ms.spacegrant.org/uploads/images/Education/Conferences/NASA%20s%20Toy%20Box/2.ton.hockey.pucks.pdf
Parker, Steve. How the Body Works, London: Dorling Kindersley Limited, 1994.
Ressler, Sandy. National Institute of Standards and Technology, Visualization and Usability Group, OVRT Resources for the Humanoid Animation Working Group.
University of British Columbia, Department of Zoology, "Al's Website," http://www.zoology.ubc.ca/~biomania/tutorial/bonejt/anc07.htm
U.S. Department of Health and Human Services, National Institutes of Health, National Institute on Aging, Health Information, Publications, "Age Page: Arthritis Advice," May 2005.
Jessica Todd, Sara Born, Abigail Watrous, Denali Lander, Beth Myers, Malinda Schaefer Zarske, Janet Yowell
© 2006 by Regents of the University of Colorado.
Integrated Teaching and Learning Program, College of Engineering, University of Colorado Boulder
Last modified: November 25, 2015