In the context of kinetic friction, what effect does friction have on an object sliding across a surface?

• A. It has no effect on the object once it is moving at constant speed.
• B. It exerts a force opposite the direction of motion, tending to slow the object down.
• C. It exerts a force in the same direction as the motion, tending to speed the object up.
• D. It acts perpendicular to the surface and increases the normal force.

Answer: (B)

Verified step by step guidance

1. Understand that kinetic friction is a force that acts between two surfaces in relative motion, specifically when an object is sliding over a surface.
2. Recall that frictional force always acts to oppose the relative motion between surfaces, meaning it acts opposite to the direction of the object's velocity.
3. Recognize that because kinetic friction opposes motion, it tends to slow down the object sliding across the surface, reducing its speed unless an external force maintains it.
4. Note that kinetic friction does not act perpendicular to the surface; instead, the normal force acts perpendicular, and friction acts parallel to the surface.
5. Conclude that the correct effect of kinetic friction on a sliding object is that it exerts a force opposite the direction of motion, tending to slow the object down.