Lesson: Gravitational Potential Energy Physics • 9th Grade

In this lesson, we will learn how to calculate changes in the energy of an object in a gravitational field using the definition of the gravitational potential energy, E = mgh.

Lesson Plan

Objectives

Students will be able to

define a change in gravitational potential energy as the work done on an object by the force of gravity,
apply the formula gravitational potential energy to find any of the terms in the formula,
recall that and deduce that .

Prerequisites

Students should already be familiar with

the principle of conservation of energy treated qualitatively,
work = force × distance,
weight = mass × acceleration due to gravity.

Exclusions

Students will not cover

any motion of Earth due to its gravitational attraction to an object at some distance from it.
the internal structure of Earth,
reference points.

Lesson Video

Sample Question Videos

01:31
02:36
04:38

Lesson Worksheet

Q1:

A bird flying over the sea has a weight of 15 N and has a constant 765 J of gravitational potential energy. How far above the sea does the bird fly?

Q2:

A woman walks along a bridge, holding in her hand a small cell phone with a weight of 0.75 N. The phone is held at a height of 1.2 m above the surface of the bridge. The bridge is 4.3 m above the surface of a river. How much greater is the gravitational potential energy of the phone held in the woman’s hand on the bridge than the gravitational potential energy of the phone at the surface of the river?

Q3:

A speck of dust with a mass of 0.22 g is at a distance of 1,250 m from a tiny shard of ice that has a mass of 1.5 g. Both of the objects are located in deep space, extremely far away from any stars or other objects of any kind. The gravitational force that the objects exert on each other is negligible, as is the gravitational force on either the speck of dust or on the shard of ice from any other objects.

What is the gravitational potential energy of the speck of dust?

What is the gravitational potential energy of the shard of ice?