Editing Ball (section)

==Physics==
In [[sports]], many modern balls are pressurized. Some are pressurized at the factory (e.g. [[tennis]], [[squash (sport)]]) and others are pressurized by users (e.g. [[volleyball]], [[basketball]], [[football]]). Almost all pressurized balls gradually leak air. If the ball is factory pressurized, there is usually a rule about whether the ball retains sufficient pressure to remain playable.<ref>{{Cite web |date=2015-08-10 |title=Preparing the Footballs for NFL Games {{!}} NFL Football Operations |url=https://operations.nfl.com/updates/the-game/preparing-the-footballs-for-nfl-games/ |access-date=2023-11-01 |website=operations.nfl.com |language=en-US}}</ref><ref>{{Cite web |last=LaCombe |first=Ronnie |title=How much air can fit in a basketball? |url=https://www.columbiatribune.com/story/lifestyle/family/2018/04/03/how-much-air-can-fit/985314007/ |access-date=2023-11-02 |website=Columbia Daily Tribune |language=en-US}}</ref> Depressurized balls lack bounce and are often termed "dead". In extreme cases, a dead ball becomes flaccid. If the ball is pressured on use, there are generally rules about how the ball is pressurized before the match, and when (or whether) the ball can be repressurized or replaced.

Due to the [[ideal gas law]], ball pressure is a function of temperature, generally tracking ambient conditions. Softer balls that are struck hard (especially squash balls) increase in temperature due to [[inelastic collision]].

In outdoor sports, wet balls play differently than dry balls. In indoor sports, balls may become damp due to hand sweat. Any form of humidity or dampness will affect a ball's surface friction, which will alter a player's ability to impart spin on the ball. The action required to apply spin to a ball is governed by the physics of [[angular momentum]]. Spinning balls travelling through air (technically a [[fluid mechanics|fluid]]) will experience the [[Magnus effect]], which can produce lateral deflections in addition to the normal up-down curvature induced by a combination of [[wind resistance]] and [[gravity]].
<gallery>
File:Green Rubber Band Ball.jpg|[[Rubber band ball]]
File:Black Super Ball.jpg|[[Super Ball]]
File:A cherry utility ball in a field (cropped).jpg|[[Utility ball]]
File:Sponge Ball.jpg|Sponge ball
</gallery>