Join Two Bones

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life sciences,
physical sciences






one class period


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Students will learn how ... hinge joints work by building a biomechanical [definition] model. How the backbone (vertebrae) work together by building a biomechanical model.

Background Information

Your students can see the principles behind the body's joints by making wooden models. The hingelike elbow joint connects the humerus [definition] of the upper arm and the paired radius and the ulna of the lower arm. The elbow joint can only move in one plane.

Your backbone (vertebrae [definition]) is a series of bones joined together. Each bone (vertebra) is separated by a pad of cartilage [definition] and held in place by strong muscles [definition] and ligaments [definition]. Each joint moves a small amount, but there are many joints so your spine can bend.

This activity gives your students a closer look at how joints (the area where bones meet) work.



For each team of students:

Procedure A:

  • Wood (2 equal length pieces of 1 inch by 2 inch board).
  • Hinge (choose a size that fits the pieces of wood).
  • Screws (for the hinge).
  • Screwdriver.
  • Rubber bands.
  • Dishwashing sponge.

Procedure B:

  • Wood (2 T-shaped pieces, see illustration).
  • Rubber bands.
  • Dishwashing sponge.


Bend your elbow. How does it work?

Stand up and bend at the waist.

How do you think your backbone (vertebrae) works?

Procedure A

  1. Take two pieces of wood of equal size.
  2. Use a hinge to join the two ends.
  3. You now have an elbow joint. The hinge at this joint can fully close to allow the mechanical arm to bend inward. The hinge can open up to 180 degrees but no farther, just like your elbow.

Procedure B

  1. Take two pieces of T-shaped wood. Place the Ts opposite one another (see diagram).
  2. Between the T's add a piece of sponge.
  3. Place a rubber band around the Ts to hold the sponge in place. The T's are vertebra. The sponge is cartilage and the rubber bands are ligaments.


Compare the movement in the mechanical elbow with the mechanical backbone (vertebrae). What are the similarities? What are the differences?

Compare the movement in the mechanical elbow and backbone (vertebrae) to your elbow and backbone. What are the similarities? What are the differences?

Are bones joined together differently? Why? How does creating a biomechanical model help you understand what¹s going on inside you?

Adapted from

Burnie, David. How Nature Works. Pleasantville, NY: Reader¹s Digest Association, Inc., 1991.

Additional Sources

Whitfield, Philip, ed. The Human Body Explained. First ed., New York: Henry Holt and Company, 1995.