Friction

• Friction always opposes the direction of motion or the direction it is about to move in
• If static, $F_r\ \le\mu R$
• If limiting equilibrium/dynamic,

  $F_r\ =$$\ \mu R$
• In all situations:

  $\mu\ \ge\ 0$
• Label the forces on this diagram:

  A) Fr

  B) mg

  C) mg sin θ

  
• If $mg\ \sin\ \theta\ <\ F_{rMAX}$ the object will move down

  
• If $mg\ \sin\ \theta\ \le\ F_r$ it will remain at rest
• To resolve forces, you split them into two components: horizontal and vertical
• To calculate the horizontol force from F you use: $F\ \cos\ \theta$
• To calculate the vertical force from F you use: $F\ \sin\ \theta$
• Which way are the arrows going (right/left) under tension?

  A) right

  B) left

  
• Which way are the arrows going (right/left) under thrust?

  A) left

  B) right