Magnus effect: how spin steers the ball
About this app
Same shot, three spins: topspin dips early, slice floats long, without spin in between. In the magnifier the air flows around the spinning ball, the wake is deflected and arrows show weight, drag and the Magnus force. Groundstroke and lob, padel or tennis ball.
With explain mode: an AI tutor walks you through the app, points out what matters in the scene and answers your questions.
What the Magnus effect is
A spinning ball drags the air at its surface along a little. On the side that moves with the airflow the air flows faster and follows the ball further; behind the ball the airflow is deflected to the other side. The reaction on the ball is the Magnus force, perpendicular to the direction of flight. It grows with the square of the speed: F = ½·ρ·A·C_L·v². With topspin it points down, with slice up.
What the app shows
At the top the same shot flies three times: with topspin, without spin and with backspin, plus the dashed path without air. At 72 km/h and 2500 revolutions per minute the topspin ball lands after 11.8 m, the ball without spin after 13.9 m and the slice only after 17.1 m. Below, a magnifier shows the airflow around the spinning ball and three force arrows: weight, drag and Magnus force.
Try it yourself
The sliders change speed, launch angle and spin rate, and you see how far the paths spread apart. The magnifier switches between topspin, no spin and slice; the arrows turn with the direction of flight. In the lob the app shows why a topspin lob lands in time before the back wall. For comparison the padel ball can be swapped for a tennis ball.
Frequently asked questions
- What is the Magnus effect?
- A force on a spinning body moving through air. The spin deflects the air behind the ball to one side, and the ball is pushed to the other side, perpendicular to its direction of flight.
- Why does a topspin ball drop faster?
- With topspin the Magnus force points down and adds to the weight. The ball drops earlier and more steeply. It does not get faster, but it can be hit harder without going out.
- How large is the Magnus force on a padel ball?
- In the app’s model, at 72 km/h and 2500 revolutions per minute about 0.19 N, roughly a third of the 0.57 N weight. Drag at this speed is about 0.44 N.
- What can I try in this app?
- You change speed, angle and spin rate, compare three paths and the path without air, and see airflow and forces on the ball in the magnifier. Plus a lob and a tennis ball for comparison.
Subject: Sport & rules
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