# Magnus Effect and Nothing but Net

Here is a cool video explaining the Magnus Effect. Under the Magnus effect, topspin produces a downward swerve of a moving ball, greater than would be produced by gravity alone, and backspin has the opposite effect.

Spin will certainly have an effect on the shots being made for NbN. How much will spin effect accuracy and distance?

Does the effect take effect the second a ball would leave a launcher? In the video, it did not seem like the ball was affected until a certain speed was reached?

When you take a ball from rest and launch it a particular speed with spin it will initially have half the predicted lift. The lift will increase according to Wagner’s function where it will have about 90% of the predicted lift after traveling about 7 diameters.

Thanks, this is helpful information :).

Anytime! Keep in mind that this is assuming that the ball does not accelerate (or decelerate) much after the initial velocity impulse. Also, it assumes the ball is being shot in an area of still air.

Because the basketball in the video is accelerating as it falls and because there appears to be a strong breeze, the lift over time probably doesn’t follow Wagner’s function. However, the idea is still there that the lift will build up over time in a reasonably similar fashion.

If you are further interested in the subject I can dig up some resources. If I recall, the Magnus page on Wikipedia only has a little blerb on it. Because it’s a function derived from empirical results that only applies to a smooth-ish ball launched from rest, there isn’t much text available online.

well that effect is relative to the rotational velocity of the ball, and yes it could be said that immediately after the ball leaves the launcher the effect takes place. How much the ball “swerves” after leaving the launcher is fully dependant of the rotational velocity of the ball. the force of the magnus effect is F = ClAd*v^2/2, and the lift generated(Cl) is Cl = 1/[2+(V/Vspin)],
Vspin = RW, r = radius, and W = rotational velocity, for example it takes 80 rpms to get a Cl of .2 of course this is minuscule and unless you are using a single wheel launcher or purposely spinning the ball this will not a very large factor, I would recommend if you are using a two wheeled launcher to have the wheel tied together(aka you spin one wheel and the other spins also).

It’s been my theory that topspin may be preferred as the opening size increases as the downward entry trajectory steepens. This run counter to the typical basketball analogy, but still seem logical. I’ll be testing both…

top spin is actually best when the target it straight ahead and a wide target rather than a tall small target. back spin gives more room for error because it slows the ball down in the air. top spin accelerates the ball and the effect of the spin is proportional to the speed as well as distance. Thats why basketball utilizes backspin

This formula looks wrong. Dimensional analysis does not yield force as the units but instead gives force per time squared. Also, it looks like it was made for a cylinder and hasn’t been modified for a sphere. Here is a NASA image that has all the math and such, just make sure you use the correct units and direction for spin!

The above formula does have some limits as to how large the velocity and spin can be before you get into a large enough Reynolds’s number that you get some weird partial turbulence that complicates things greatly. You really wouldn’t get into the range for NbN unless you are trying a cross-field shot with a lot of spin.

Yes, but there’s more. In Cameron’s documentary
https://www.youtube.com/watch?v=K-YNZEYdv8U he mentions that the single flywheel gives a lot of backspin, and thus has very good accuracy but very poor distance. As he goes to 2 flywheels, but spins the bottom one faster than the top one and thus provides backspin, the ball becomes slightly less accurate but goes much farther. However, when he gets no spin whatsoever, the ball is much less accurate because it does not have gyroscopic stability.

Getting back to the original point and away from the math, using the Magnus Effect to maximize distance by providing a small amount of backspin can increase accuracy significantly and only dampen distance slightly.

This can be seen in baseball with knuckle ball pitchers. These pitchers are able to throw the ball with little to no spin, thus the ball breaks randomly (at least from the hitter’s perspective) as it approaches home plate. The opposite, the so-called “four seam fastball,” uses the Magnus Effect to drop less steeply than if gravity alone was in charge by getting a huge amount of backspin and using the seams to grip the air. In this analogy, the knuckle ball is the double flywheel that provides no spin and the fastball is the bottom flywheel spinning faster than the top one. It is obvious which alternative is more desirable when trying to shoot balls into a small goal from a long distance consistently.

Sorry for the excessive length, and I hope this helps.