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The effect of spin on the flow behind a sphere.The following photographs show you the effect of spin on the flow behind a golf ball. The experiments were performed in the small water tunnel [link], with a mean flow velocity of 3.8 centimeters per second. In the first two pictures, the golfball isn't spinning. In the third, it's spinning with 7 revolutions per minute (rpm), and in the fourth with 12 rpm.In photo 1, the streaks are made by small particles suspended in the water. The shutter time was 1/8th of a second, so that the paths the particles follow during that time become visible. You can clearly see a region behind the golf ball where the flow is very different from the flow around it. This is called the wake. Here, the flow speed is smaller, and recirculation of the flow occurs.  1. With dye, more details become visible. In the second photo, where the conditions are equal to those in the fist, you can see that vortices are being shed from the ball.  2. In pictures three and four, you can clearly see the effect of spin. Now, the golfball is spinning in a clockwise direction, and the wake is directed downwards. In picture 4 the ball is spinning faster, and the angle of the wake is steeper.  3.  4.
Pictures taken by Michel van Rooij,
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