Activity 3A: Levers in the Body: They Are Not What You Might Think!

Students will be surprised to learn that the levers in their arm don’t behave as expected! They will use a model of the human arm, including an artistically modified scapula, humerus, radius and ulna. After measuring the weight of the forearm on their model with a spring scale, they will assemble the bones so that the elbow joint is movable. Once students have assembled the model, they will attach string “biceps and triceps muscles” to the model at origin points labeled on the model. An approximation of the actual insertion point will be labeled on the model and the other end of the string “muscle” attached to that location. The student will then investigate how the biceps muscle operates the joint as a lever system, exploring angles and the resistance and effort forces. Next, students will move the insertion point of the string muscle to examine how the lever system changes. Both the triceps and biceps will be studied in this part of the activity. Finally, using body segment weight percentages, students will relate their findings to their own bodies.