There are two types of frictions that you should consider. They are static friction and kinetic friction. Static friction is the friction that keeps an object from moving, and the force resulting from it can be seen in equation 1. While kinetic friction is the friction that slows an object down once it starts moving. Refer to equation 2 to calculate the force caused by kinetic friction.

(Eq 1)  $f=μ_sW,μ_s=coefficient~of~static~friction

(Eq 2)  $f=μ_kW,μ_k=coefficient~of~kinetic~friction

Notice that both static and dynamic friction are a production of the objects weight. This means that the coefficients of static friction and kinetic friction are unit less. Also, the coefficient of static friction is larger than the coefficient of kinetic friction, which means the resulting force from static friction is greater than the resulting force from kinetic friction.

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