I recently answered this question: Laminar Versus Turbulent Flow and it caused me to think of the following situation.
Given that an (American) football weighs between Football 400 to 430 grams, and a (FIFA Rules) soccer ball is in the same weight range, 410 to 450 grams, which will travel further, when thrown under the same conditions?
I am assuming both are the same weight, say 420 grams, and both are fired into still air at the same angle, say 45 degrees, by a machine that imparts the same initial velocity to both of them. Also no spin is involved, although it would be interesting to see, if the soccer ball was allowed to spin, would that reduce drag, by reason of the planar-like surfaces it is composed of, and the regular ridges between the panels?
I am assuming no spin of any kind and the same "flight path" but any answers that incorporate more realistic situations will be welcomed. It's the difference in drag that I was initially interested in, but any answer that applies reality to the problem is appreciated.
Please ignore the relative sizes shown in the picture, as these are chosen at random.
In professional play the football has a long axis of 28 cm , a long circumference of 71 cm, and a short circumference of 53 cm.
The soccer ball has a diameter of 22 cm and a circumference of 70 cm.
My guess would be the football, rather than the soccer ball, because of it's shape, and if so, can any estimate be made of the extra distance?
I do realise that this is a "novelty" type question, compared to the majority of questions received here, but I do think that there may be some interesting fluid dynamics related physics involved.
Best Answer
The drag force on an American football is in the range of a coefficient of .05 to .06. If the football is spinning the drag is slightly less.
The drag on a FIFA soccer ball is a coefficient of .25.
The football should travel further. The diameter of an NFL football is about 17.3 centimeters. The diameter of a FIFA soccer ball is roughly 22 centimeters. The greater cross sectional area of the soccer ball creates a thicker wake and more drag, as Sebastian Riese points out in his comment.
The chief difference between the balls, which produces less drag on the NFL football, is the shape. The NFL football's wake is significantly thinner than the soccer ball's, to a great extent because of the shape of the ball. The hulls of ships, for example, are designed like a football's shape below the water line toward the stern in order to allow a more laminar flow as the boundary layer separates from the back of the hull. Laminar flow creates a thinner wake which produces less turbulent viscous drag.