Lesson: Newton’s Second Law of Motion Physics • 9th Grade

In this lesson, we will learn how to apply Newton’s second law of motion, F = ma, to find the accelerations caused by forces that act in various directions.

Lesson Plan

Objectives

Students will be able to

use the formula in all combinations, where can be the resultant of multiple forces acting along a line in the same or opposite directions,
substitute the value of calculated using into kinematic formulas,
substitute the value of calculated using kinematic formulas into ,
substitute the value of determined using kinematic graphs into .

Prerequisites

Students should already be familiar with

velocity,
acceleration,
free-body force diagrams.

Exclusions

Students will not cover

variable mass bodies,
Newton’s third law of motion.

Lesson Video

Sample Question Videos

05:38
02:10
05:21

Lesson Worksheet

Q1:

A cell phone is at rest on a tabletop and the phone’s owner flicks the phone with their fingers, which applies a 0.01 N force to the phone. The phone is accelerated at a rate of 0.1 m/s² in the direction of the flick. What is the mass of the phone?

Q2:

A cup of mass 125 g is at rest on a desk when it is accidentally knocked by a person’s arm. The cup accelerates in the direction that it is pushed at a rate of 0.25 m/s². How much force is applied by the arm that knocks the cup? Give your answer to two significant figures.

Q3:

An object of mass 1.5 kg has a force of 4.5 N applied to it. At what rate does the force accelerate the object?