How do drag, lift and spin affect the movement of bodies and objects in sport?
The factors affecting air and water resistance (drag), how lift is created by the Bernoulli principle, and the Magnus effect that makes a spinning ball swerve.
A focused answer to OCR A-Level PE on fluid mechanics: the factors affecting drag (velocity, frontal area, shape and surface), laminar and turbulent flow, how lift is created through the Bernoulli principle, and how the Magnus effect makes topspin, backspin and sidespin swerve a ball.
Reviewed by: AI editorial process; not yet individually human-reviewed
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What this dot point is asking
OCR wants you to explain the factors affecting drag, distinguish laminar and turbulent flow, explain how lift is created through the Bernoulli principle, and explain the Magnus effect for topspin, backspin and sidespin.
Drag and its factors
Athletes reduce drag by streamlining: a cyclist or skier crouches to cut frontal area, wears tight, smooth clothing and an aerodynamic helmet, and uses streamlined equipment; a swimmer wears a smooth suit and cap and holds a streamlined body line. Drafting (following close behind another competitor) reduces the drag on the trailing athlete.
Laminar and turbulent flow
Lift and the Bernoulli principle
The Magnus effect and spin
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 marksState the factors that affect the air resistance acting on a cyclist, and describe one way a cyclist reduces drag.Show worked answer →
A Component 01 Section C application question. Marks for the factors and a valid drag-reduction strategy.
Award marks for: air resistance (drag) increases with the velocity of the cyclist (rising sharply at higher speeds), the frontal cross-sectional area presented to the air, the shape (streamlining) of the body and bike, and the smoothness of the surface. A cyclist reduces drag by adopting a low, crouched, streamlined position to reduce the frontal area, wearing tight, smooth clothing and an aerodynamic helmet, and using a streamlined bike frame and wheels; drafting behind another rider also reduces drag.
Markers reward the named factors (velocity, frontal area, shape, surface) and a genuine streamlining strategy that reduces frontal area or smooths the surface.
OCR 20216 marksExplain, using the Magnus effect and the Bernoulli principle, why a football struck with topspin dips more steeply than one struck without spin.Show worked answer →
A Component 01 Section C extended-response question. Markers reward the pressure-difference mechanism and the correct direction of the force.
Award marks for: a ball with topspin rotates so that the top surface moves backward against the airflow and the bottom surface moves forward with it. By the Bernoulli principle, the air travels faster (and pressure is lower) on the side where the surface moves with the airflow, and slower (higher pressure) on the side where it moves against it. With topspin the air moves faster under the ball and slower over the top, so pressure is higher above and lower below, creating a downward Magnus force. This downward force adds to gravity, so the ball dips more steeply than a ball with no spin, which only follows the parabola set by gravity.
A top answer links the spin direction to the faster, lower-pressure airflow, then to a downward net force that steepens the dip.
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Sources & how we know this
- OCR A Level Physical Education (H555) specification — OCR (2016)