The Magnus Effect

Gustav Magnus was a German scientist in the 19th century, most known for experimentally testing The Magnus Effect. In 1853, he detailed this explanation of the effect; A spinning object moving through a fluid, departing from its straight path because of pressure differences that develop in the fluid due to changes in velocity induced by the spinning body.

The Magnus effect is a particular manifestation of Bernoulli’s theorem– fluid pressure decreases at points where the speed of the fluid increases. To elaborate, Bernoulli’s principle asserts that an increase in a fluid’s speed happens at the same time as a drop in static pressure or a decrease in the fluid’s potential energy. In the case of a ball spinning through the air, the turning ball drags some of the air around with it. Viewed from the position of the ball, the air is rushing by on all sides. The drag of the side of the ball turning into the air retards the airflow, whereas on the other side the drag speeds up the airflow. Greater pressure on the side where the airflow is slowed down forces the ball in the direction of the low-pressure region on the opposite side, where a relative increase in airflow occurs. He tested the effect, which alters the trajectory of a spinning artillery shell and is responsible for the curve of a served tennis ball or a driven golf ball.

A spinning object in motion exerts a net force on the air, which according to Newton’s 3rd law exerts an equal and opposite force back on the moving and spinning object, altering its trajectory.

However, Isaac Newton, after witnessing tennis players at Cambridge college, had already described it back in 1672 and accurately identified the cause. In 1742, Benjamin Robins, a British mathematician, ballistics researcher, and military engineer, is said to have explained discrepancies in musket projectile trajectories in terms of the Magnus effect.

There have been numerous inventive applications of the Magnus effect in our daily lives. Anton Flettner, a German engineer, proposed replacing a vessel’s sail with rotors in the 1920s. The Magnus effect, it was anticipated, would provide a thrust several times that of an equivalent sail area in a crosswind.

Writer: Golda Abs

Editor: Uzay Kara/Omar Alturki

References:


1- “Library.SCOTCH: Biomechanics: The Bernoulli Principle and the Magnus Effect: The Magnus Effect.” – – Home – – Library.SCOTCH at Scotch College, https://library.scotch.wa.edu.au/healthandphysicaleducation/year12/biomechanics/themagnuseffect


2- What Is the Magnus Effect, http://ffden-2.phys.uaf.edu/211_fall2010.web.dir/Patrick_Brandon/what_is_the_magnus_effect.html?