Update 109-friction.md (#5386)

IB diploma vid discussing friction basics

src/data/roadmaps/game-developer/content/102-game-physics/100-dynamics/109-friction.md

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 # Friction
 
 `Friction` is a crucial concept in game dynamics. In the context of games, it's typically used to slow down or impede movement, providing a realistic feel to characters or objects movement. For example, when a player's character runs on a smooth surface as compared to a rough one, friction influences the speed and control of that character. It can be seen in how cars skid on icy surfaces, how walking speed changes depending on the terrain, or how a ball rolls and eventually slows. The equation to compute friction is usually `f = μN`, where `f` is the force of friction, `μ` is the coefficient of friction (which depends on the two surfaces interacting), and `N` is the normal force (which is generally the weight of the object). You can adjust the coefficient of friction in a game to have different effects depending upon the desired outcome.
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+- [Friction](https://youtu.be/t1HWIoDUWXg?si=FmFsIGTSHpLS72vp)