Which type of friction resists the start of motion when surfaces are at rest relative to each other?

Which type of friction resists the start of motion when surfaces are at rest relative to each other?

• A. Static
• B. Kinetic
• C. Rolling
• D. Viscous

Answer: (A)

Static friction is the force that resists the start of motion between two surfaces that are at rest relative to each other. It can adjust its value up to a maximum limit to prevent slipping, and that maximum is determined by the coefficient of static friction and the normal force: F_s,max = μ_s N. As you push, static friction rises to match your effort until you reach that limit; once your push exceeds it, motion begins and friction transitions to kinetic friction, which is typically smaller (F_k = μ_k N). Why the others don’t fit here: kinetic friction acts once motion has already started, not to prevent the initial movement; rolling friction relates to objects that roll rather than slide, so it isn’t about starting sliding between two surfaces at rest; viscous friction involves resistance in fluids, not dry contact between solid surfaces at rest.

Static friction is the force that resists the start of motion between two surfaces that are at rest relative to each other. It can adjust its value up to a maximum limit to prevent slipping, and that maximum is determined by the coefficient of static friction and the normal force: F_s,max = μ_s N. As you push, static friction rises to match your effort until you reach that limit; once your push exceeds it, motion begins and friction transitions to kinetic friction, which is typically smaller (F_k = μ_k N).

Why the others don’t fit here: kinetic friction acts once motion has already started, not to prevent the initial movement; rolling friction relates to objects that roll rather than slide, so it isn’t about starting sliding between two surfaces at rest; viscous friction involves resistance in fluids, not dry contact between solid surfaces at rest.