Lesson: Kinetic Friction Physics • 9th Grade

In this lesson, we will learn how to analyze the forces acting on objects on frictional surfaces when they move along these surfaces.

Lesson Plan

Students will be able to

define the coefficient of kinetic friction, , using , where is an applied force parallel to a frictional surface that makes an angle with the horizontal,
understand how to determine the kinetic friction force on a moving object,
calculate the coefficient of kinetic friction between two surfaces.

Lesson Video

Lesson Worksheet

Q1:

A stone with a mass of 8.2 kg is initially at rest on a rough surface. The coefficient of static friction between the stone and the surface is 0.70, and the coefficient of kinetic friction between the stone and the surface is 0.60. A force is applied to the stone parallel to the surface that negligibly exceeds the force required to make the stone move across the surface. What is the magnitude of the acceleration of the stone across the surface?

Q2:

A refrigerator with a mass of 105 kg is pushed a distance of 0.333 m across a rough horizontal surface. Moving the refrigerator dissipates 205 J of energy. What is the coefficient of kinetic friction of the refrigerator with the surface?

Q3:

A cup is pushed so that it slides along a rough tabletop, decelerating at 4.4 m/s². What is the coefficient of kinetic friction between the cup and the tabletop?