The human body contains a few different types of joints. One of them, the hinge joint, is found in the elbow and knee. A hinge joint allows a body part to move in only two directions, out and in, like a door hinge. As a student or a teacher, you can make a model of an elbow joint and demonstrate how the hinge works.
- Two craft sticks (tongue depressors)
- Two large and two small rubber bands
- Thin-tip permanent marker
Set the two craft sticks on top of one another at a 90-degree angle to form an "L" shape.
Wrap the small rubber bands around the two touching ends of the craft sticks in an "X" shape to hold the sticks together in the "L" position. Wrap the rubber bands tightly enough that the craft sticks do not slip out of position, but loose enough to bend together and apart from one another at the non-attached ends like a hinge.
Cut two notches in the vertical stick: one just under where the craft stick is rounded at the top on the left side of the vertical stick, and the other slightly lower than the first, on the right side of the vertical stick.
Cut two more notches in the horizontal stick. One notch goes on top of the horizontal stick, right next to where it meets the vertical stick and to the left of the vertical stick. The other notch goes on the end of the horizontal stick, to the right of the vertical stick, right in the middle of the curve on the end of the horizontal stick.
Wedge the ends of the large rubber bands into the notches on the craft sticks. The rubber bands run from the top of the "L" shape to the bottom on each side of the vertical stick. In other words, the rubber band runs from the top of the vertical stick to the bottom notch, one rubber band on the left of the vertical stick, and one on the right.
Using the marker, label the vertical stick "Humerus."
Draw a line running down the middle of the length of the horizontal stick with the marker. Label the area above the line "Radius," and label the area below the line "Ulna."
Move the sticks back and forth, allowing the rubber band "X" to demonstrate the hinge joint that is found in an elbow.