You probably know most kinds of sports balls, but have you ever compared their mathematical details?
(Yes, I know a shot is not a ball and 10-pin bowling is not done outside)
Balls are described as having a certain diameter or circumference. And usually the weight and material are controlled as well. You can compare these specifications with the image I created here.
Some balls, like volleyballs and soccer balls, are made of panels sewn together. These and other balls that are hollow may be inflated to a certain size or firmness. In the case of these balls the inflation pressures might be specified by the sport authorities.
The balls used in some other sports, like American football and rugby are not round, so I have not included them here.
You also might see another kind of round, circular object at this time of the year: the wheels on the bicycles ridden in the Tour de France.
Wheels are measured in diameter. The rims are a certain width and depth. We count the spokes too.
Bike wheels are a specialized business, and the "big boys" in the business have been at it for a long time. I used to run a bike shop back in the 'Seventies and I got parts from the same people that are still fixing bikes today.
To finish this off, here are some other spherical objects I saw over the weekend.