(M1) What direction does friction act in? What are the friction equations both generally and in limiting equilibrium? What does it mean for a system to be in equilibrium?

Friction always acts in the opposite direction to motion (or the potential motion) and Friction (Fr) acts as follows: In every case: Fr ≤ 𝜇R (where 𝜇 is the coefficient of friction and R is the reaction force) In limiting equilibrium: Fr= 𝜇R For a system to be in equilibrium then the resultant force of the combination of all the vectors must be zero