The result is a tough material that has a low coefficient of friction comparable to that of Teflon and is highly resistant to abrasion.

ECONOMIST: Skiing: Not waxing lyrical | The

To make more sense of this, the International Tennis Federation, the game's law-makers, have produced a chart which simply matches the coefficient of friction (friction) and coefficient of restitution (bounce) to produce a court pace rating.

CNN: Tennis interactive: Why clay is so different

The virality of a messaging platform equals its emotion-friction ratio, and the Snapchat paradigm maximizes this virality coefficient.

FORBES: Snapchat Takes Over Yale With Viral Growth That Sends Facebook Back To School