Which force opposes motion between two surfaces in contact?

Which force opposes motion between two surfaces in contact?

• A. Friction
• B. Applied force
• C. Gravitational force
• D. Normal force

Answer: (A)

Friction is the force that opposes motion between two surfaces in contact. It acts parallel to the interface and points opposite to the direction in which the surfaces would slide. When you push a block along a surface, friction resists that motion by pointing the other way. There are two main kinds: static friction, which prevents motion up to a limit if the surfaces aren’t sliding yet, and kinetic (sliding) friction, which acts when the surfaces do slide and is usually smaller in magnitude. Other forces at play don’t inherently oppose motion along the contact surface. The normal force is the perpendicular reaction that keeps the surfaces pressed together; it acts normal to the contact and doesn’t oppose motion along the surface. Gravitational force pulls downward and influences the normal force, but it doesn’t resist the sliding motion itself. An applied force is any external push or pull; it can help or hinder motion, but the force that specifically resists sliding between the surfaces is friction.

Friction is the force that opposes motion between two surfaces in contact. It acts parallel to the interface and points opposite to the direction in which the surfaces would slide. When you push a block along a surface, friction resists that motion by pointing the other way. There are two main kinds: static friction, which prevents motion up to a limit if the surfaces aren’t sliding yet, and kinetic (sliding) friction, which acts when the surfaces do slide and is usually smaller in magnitude.

Other forces at play don’t inherently oppose motion along the contact surface. The normal force is the perpendicular reaction that keeps the surfaces pressed together; it acts normal to the contact and doesn’t oppose motion along the surface. Gravitational force pulls downward and influences the normal force, but it doesn’t resist the sliding motion itself. An applied force is any external push or pull; it can help or hinder motion, but the force that specifically resists sliding between the surfaces is friction.