What is static friction?

What is static friction?

• A. The resistance to motion when an object is moving.
• B. The friction that makes rolling possible.
• C. The friction due to air.
• D. The force exerted between two surfaces by weight alone.

Answer: (D)

Static friction is the force that resists starting to slide between two surfaces that are in contact but at rest relative to each other. Its magnitude adjusts to match the applied sideways push up to a maximum value, which is μs times the normal force between the surfaces. The normal force is the perpendicular contact force; on a horizontal surface it often equals the weight, but friction isn’t caused by weight alone. It arises from the microscopic interactions at the contact between the surfaces. If the push is smaller than μsN, the surfaces don’t move and static friction exactly counteracts the push. When the push exceeds μsN, motion begins and kinetic friction takes over, usually with a smaller friction coefficient. The other descriptions refer to different kinds of resistance: rolling friction relates to objects that roll, and air resistance is drag from the surrounding air.

Static friction is the force that resists starting to slide between two surfaces that are in contact but at rest relative to each other. Its magnitude adjusts to match the applied sideways push up to a maximum value, which is μs times the normal force between the surfaces. The normal force is the perpendicular contact force; on a horizontal surface it often equals the weight, but friction isn’t caused by weight alone. It arises from the microscopic interactions at the contact between the surfaces. If the push is smaller than μsN, the surfaces don’t move and static friction exactly counteracts the push. When the push exceeds μsN, motion begins and kinetic friction takes over, usually with a smaller friction coefficient. The other descriptions refer to different kinds of resistance: rolling friction relates to objects that roll, and air resistance is drag from the surrounding air.