Explanation

For this simulation, wind tunnel data taken by P.W. Bearman and J.K. Harvey- 1 have been used. The same data were also used for the figures below. For more information please refer to the article.

Drag on a ball

When a ball flies through the air, there will be a force acting on the ball in the opposite direction of the velocity. We can divide this force into two different forces:

The skin friction is the force that is acting along the surface of the ball. At the surface of the ball, there will be a very thin layer of air (boundary layer), which has at the outer side the velocity of the air and at the inner side the surface velocity of the ball. Within this layer the different air particles will interact with each other. This will cause the friction.

The pressure drag on the ball however will cause a much larger force than the skin friction. The pressure drag is the force, which will act because of separation from the boundary layer from the surface of the ball. This will happen because the air particles can not follow the curved surface of the ball anymore. Behind the ball there will be a wake, where the pressure is much lower. The wake will suck the ball in the opposite direction of the velocity.

For the effect of dimples on a golf ball please refer to the Scientific American web page.

Spinning perpendicular to the ball's velocity will cause a force perpendicular to the spinning and perpendicular to its velocity, which is known as the Magnus effect. This effect will cause a difference in pressure between both sides of the ball. This will create a force in the direction of the low pressure.

The effect on the moon

On the moon there are two things different from the Earth:

The ball will fly much farther on the moon because of a lack of atmosphere. There will be no aerodynamic force acting on the ball, no lift and no drag.

The ball will also fly much farther on the moon because of a less gravity force.

REFERENCE

1        P.W. Bearman and J.K. Harvey Golf ball aerodynamics, Aeronautical Quarterly,   pp. 112 - 122, May 1976.

(Menko Wisse supervised by H. Higuchi)


Simulation Applet