Measuring the Effects of the Magnus Force on Spherical Objects

Flow over a rotating sphere is of significant interest in many sports such as basketball, baseball, and lacrosse, because all the balls used in these activities translate and rotate simultaneously (Inverse Magnus Effect). The Magnus effect is the force exerted on a rapidly spinning cylinder or sphere moving through a fluid in a direction perpendicular to the axis of rotation; this force is the reason balls curve in mid-flight. I used the dynamometer to measure this force, along with the drag forces, on a ball subjected to 100 mph winds produced in the ME wind tunnel. The experiment was conducted to control the spin ratio, which is the ratio of the objects angular velocity to the free-stream velocity. I analyzed two different types of balls, a baseball and a golf ball. The baseball was rotated with a spin ratio of 0.376, or 4300 RPM’s at a free-stream velocity of 100 MPH, which produced a force of 1.333 N. Increasing the spin ratio to 0.5370, by maintaining angular velocity of 4300 RPM’s but reducing the free-stream velocity to 70 MPH, produced a force of only 0.6407 N. While the assumption of having a greater spin ratio correlates to a greater Magnus force may be logical, it is in practice not completely true. In fact, initial results have hinted at the fact that at high RPM’s a lower spin ratio may lead to a greater Magnus Force.