Lesson: Centripetal Force Physics • 9th Grade

In this lesson, we will learn how to analyze the magnitudes, directions, and sources of forces that act on objects moving along circular paths.

Lesson Plan

Objectives

Students will be able to

define the term centripetal force as a force acting toward a central point,
recognize that a constant centripetal force produces a constant acceleration of an object toward the center of a circular path that the object moves along at a constant speed,
calculate the magnitude of a centripetal force using and ,
recognize that and imply that and , where is centripetal acceleration,
rearrange and to find unknown values of , , and ,
determine variations in the centripetal force acting on an object in circular motion at various points along its path, where forces other than the centripetal force can act on the object,
determine forces that act on objects in circular motion to provide a centripetal force on the object.

Prerequisites

Students should already be familiar with

angular displacement,
angular velocity,
angular frequency,
Newton’s laws of motion.

Exclusions

Students will not cover

accelerated circular motion,
tangential acceleration,
elliptical motion.

Lesson Video

Sample Question Videos

15:59
16:27
03:02

Lesson Worksheet

Q1:

What is the magnitude of the centripetal force that must act on an object of mass 1.0 kg to make it move along a circular path of diameter 1.0 m, completing a circle every 1.0 s? Give your answer to the nearest newton.

Q2:

A car with mass 360 kg travels at constant speed along a circular path around a flat roundabout. The radius of the roundabout is 12 m. The car takes a time of 28 s to completely travel around the roundabout.

What is the friction force between the wheels of the car and the surface of the road? Give your answer to the nearest newton.

What is the coefficient of static friction for the wheels of the car on the surface of the road? Use a value of 9.8 m/s² for the acceleration due to gravity. Give your answer to three decimal places.

Q3:

A spinning disk has a string that holds a small sphere that has a mass of 16 g. The string is suspended from a point at a negligible distance from its center, as shown in the diagram. The disk rotates uniformly around its center with an angular velocity of 24 rad/s. The string makes an angle of with the axis of rotation of the disk.

What is the magnitude of the vertical force exerted on the sphere by the string?

What is the distance between the disk’s axis of rotation and the circular path followed by the sphere?

What is the magnitude of the horizontal force exerted on the sphere by the string?

What is the magnitude of the net force exerted on the sphere by the string?