Static friction acts to prevent sliding before motion begins.

Static friction acts to prevent sliding before motion begins.

• A. It is always larger than kinetic friction
• B. It is the friction that opposes motion when sliding
• C. It is zero when surfaces contact
• D. It acts to prevent sliding before motion begins

Answer: (D)

Static friction is the frictional force that arises when two surfaces are in contact but not moving relative to each other. It can adjust its magnitude to match the any tangential push up to a maximum value given by mu_s times the normal force. This is why it acts to prevent sliding before motion begins: as you apply a shear force, static friction rises to counteract it, keeping the objects at rest until the push exceeds mu_s N, at which point motion starts and kinetic friction takes over. The idea that friction is the force opposing motion while sliding describes kinetic friction, not static friction. And static friction isn’t necessarily zero just because surfaces touch—it can be nonzero to prevent motion. While mu_s is typically larger than mu_k, the statement that static friction is always larger isn’t the defining rule.

Static friction is the frictional force that arises when two surfaces are in contact but not moving relative to each other. It can adjust its magnitude to match the any tangential push up to a maximum value given by mu_s times the normal force. This is why it acts to prevent sliding before motion begins: as you apply a shear force, static friction rises to counteract it, keeping the objects at rest until the push exceeds mu_s N, at which point motion starts and kinetic friction takes over. The idea that friction is the force opposing motion while sliding describes kinetic friction, not static friction. And static friction isn’t necessarily zero just because surfaces touch—it can be nonzero to prevent motion. While mu_s is typically larger than mu_k, the statement that static friction is always larger isn’t the defining rule.