# Lesson Plan: Orbital Speed Physics • 9th Grade

This lesson plan includes the objectives, prerequisites, and exclusions of the lesson teaching students how to calculate the orbital speed of an object moving in a circular orbit given its orbital radius and the mass of the object it orbits.

#### 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.