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HomeAP Physics C: MechanicsPhysicsFriction, Drag, and Elasticity › Which of these matches how the source defines fr…

Which of these matches how the source defines friction?

AA force that opposes relative motion between surfaces in contact
BA force that always speeds up two sliding surfaces
CA force that exists only between perfectly smooth surfaces
DA force that pulls two surfaces directly together
Answer & Solution
Correct answer: A. A force that opposes relative motion between surfaces in contact
1. This question is asking what force resists sliding between two touching surfaces. 2. Friction is a force that opposes relative motion between surfaces in contact. 3. It never speeds an object up and it is not limited to perfectly smooth surfaces, since real surfaces are rough. 4. It also does not pull surfaces together, since it acts parallel to the contact surface, not perpendicular to it. _Source: OpenStax College Physics (CC BY 4.0), Ch 5 "Further Applications of Newton's Laws: Friction, Drag, and Elasticity", section 5.1 Friction_
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