How do the basic mechanical quantities and lever systems describe movement in sport?
The mechanical quantities of mass, weight, inertia and centre of mass, the three classes of lever and their components, and mechanical advantage and its effect on force and range of movement.
A focused answer to OCR A-Level PE on biomechanical principles and levers: the quantities of mass, weight, inertia and centre of mass and how stability depends on them, the three classes of lever and their components, and the calculation and meaning of mechanical advantage.
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What this dot point is asking
OCR wants you to define the mechanical quantities (mass, weight, inertia, centre of mass), explain how stability depends on the centre of mass and base of support, identify the three classes of lever and their components, and calculate and interpret mechanical advantage.
Mechanical quantities
For example, a kg athlete has a weight of N. Mass stays the same anywhere, but weight depends on gravity.
Centre of mass and stability
The three classes of lever
The effort arm is the distance from the fulcrum to the effort, and the load arm is the distance from the fulcrum to the load. Their relative lengths decide whether the lever favours force or speed.
Mechanical advantage
This trade-off explains sporting movement: the long, fast third-class levers at the elbow and knee let a thrower or kicker move the hand or foot a great distance very quickly, generating high speed at the end of the limb even though the muscle must work hard.
Exam-style practice questions
Practice questions written in the style of OCR exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
OCR 20184 marksA performer rises onto the balls of their feet. Identify the class of lever at the ankle, label the fulcrum, effort and load, and state whether it has a mechanical advantage.Show worked answer →
A Component 01 Section C application question. One mark for the class, one for the components, one for the arrangement and one for the mechanical advantage.
Award marks for: this is a second-class lever. The fulcrum is at the ball of the foot (the metatarsophalangeal joint), the load (body weight) acts down through the middle at the ankle, and the effort comes from the calf muscles via the Achilles tendon at the heel. Because the load is in the middle, the effort arm is longer than the load arm, so it has a mechanical advantage greater than : a small effort moves a large load.
Markers reward the load being in the middle as the defining feature of a second-class lever, and the link to a mechanical advantage above 1.
OCR 20214 marksCalculate the mechanical advantage of a lever with an effort arm of 0.4 m and a load arm of 0.1 m, and explain what the value means for movement at that joint.Show worked answer →
A Component 01 Section C calculation (use of data). Marks for the equation, the value, the no-unit point and the interpretation.
Use . The mechanical advantage is , with no unit because it is a ratio.
A value above means the effort arm is longer than the load arm, so a relatively small effort can move a large load. This favours force production over speed and range of movement, which is typical of a second-class lever.
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Sources & how we know this
- OCR A Level Physical Education (H555) specification — OCR (2016)