A spinning cricket ball swings in flight because
Correct answer: C. air moves faster on one side of the ball, creating a pressure difference across it
- A. gravity acts sideways on a spinning body
- B. the spin makes the ball lighter
- C. air moves faster on one side of the ball, creating a pressure difference across it
- D. the ball changes shape in the air
Explanation
The spinning surface drags air round with it, so the airflow is faster on one side and slower on the other, and by Bernoulli's principle the resulting pressure difference pushes the ball sideways. This sideways force on a spinning body is the Magnus effect, and it is why a swing bowler polishes one side of the ball. The same physics curves a football and lifts a golf ball.
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About Bernoulli's Equation
Bernoulli’s equation applies conservation of energy to steady flow of an incompressible, non-viscous fluid along a streamline: pressure, kinetic and gravitational terms have a constant total. It explains pressure-speed changes in narrow pipes, Venturi meters and lift, and differs from continuity because it relates pressure as well as velocity and height.
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