In this activity, students model a biceps curl using a lever system. The model measures the force1 in the biceps muscle2 when the forearm is carrying a mass3 held horizontally.
By the end of this activity, students should be able to:
- describe how the arm is an example of a lever4 (in which the elbow is a hinge)
- use a model of this hinged lever to measure the forces acting
- describe the size and direction of the forces acting on this hinged lever
- explain that the force produced by the biceps muscles pulling on the bone5 of the forearm is much greater than the load of the weight6 force at the hand.
Bent arm
Different classes of levers are identified by the way the joint and muscles attached to the bone are arranged.
For a Class 3 lever the load is further away from the pivot than the effort. There is no mechanical advantage because the effort is greater than the load. However this disadvantage is compensated with a larger movement. This type of lever system also gives us the advantage of a much greater speed of movement.
A bent arm is a Class 3 lever. The pivot is at the elbow and the forearm acts as the lever arm. The biceps muscle provides the effort (force) and bends the forearm against the weight of the forearm and any weight that the hand might be holding.
Download the Word file (see link below) for:
- introduction/background notes
- what you need
- what to do.
Nature of science
Scientists often use models to make and test predictions. For this reason, the New Zealand Curriculum’s Investigating in science achievement aim asks students to carry out science investigations using a variety of approaches, including the use of models.
- force: A push or a pull that causes an object to change its shape, direction and/or motion.
- muscle: The tissue that makes it possible for an animal to move and to maintain its posture. Muscles also make the heart beat, force blood to circulate and move food along the digestive system. The human body has more than 600 muscles.
- mass: The amount of matter an object has, measured in kilograms.
- lever : A simple machine consisting of a rigid bar (a bone) that rotates about a pivot and is used to transmit a force.
- bone: A specialised form of connective tissue. The presence of the mineral hydroxyapatite helps to give bone its strength and density.
- weight: Force due to gravity acting on an object, measured in newtons.
