Lesson: Orbital Speed Physics • 9th Grade

In this lesson, we will learn how to calculate the orbital speed of an object moving along a circular orbit given its orbital radius and the mass of the orbiting object.

Lesson Plan

Objectives

Students will be able to

know that for an object to move in a circular orbit around a large object of mass at a radial distance , it must have an orbital speed given by ,
calculate , , or using .

Prerequisites

Students should already be familiar with

the basic terminology of orbits: orbital speed, orbital period, and orbital radius,
how to use simple formulae to find the basic properties of a circular orbit (i.e., using to find the orbital period from the orbital speed and radius),
the idea that for an object moving in a circular orbit, the acceleration of the object is given by , where is the linear speed of the object and is the radius of the orbit,
the idea that the acceleration due to gravity at a point near a massive object is given by .

Exclusions

Students will not cover

noncircular orbits,
Kepler’s third law of planetary motion.

Lesson Video

Sample Question Videos

05:30
03:28

Lesson Worksheet

Q1:

A satellite follows a circular orbit around Earth at a radial distance and with an orbital speed . At what radius, in terms of , would the satellite have to orbit in order to have an orbital speed of ?

Q2:

Which line on the graph shows the relation between orbital speed and orbital radius for objects moving along circular orbits due to gravity?

Q3:

Nilesat 201 is a communications satellite that orbits Earth at a radius of 35,800 km. What is the orbital speed of Nilesat 201? Assume that the satellite follows a circular orbit. Use a value of kg for the mass of Earth and m³/kg⋅s² for the universal gravitational constant. Give your answer in scientific notation to two decimal places.