Physics Activity: Determine the acceleration of gravity & Mass of the earth with a Pendulum

 Lesson plan for using a pendulum to determine acceleration of gravity, g, and Mass of the Earth.                 Example of lab sheet for students.

A pendulum is one of the simplest devices to build and use in an experimental activity. And the main property of a pendulum we can measure and use is its period, or the time it takes a pendulum mass to be released, swing across, and then back to where it started. It turns out that by knowing the length and period of a pendulum, one can calculate the acceleration due to gravity, g. For Earth this is g = 9.8 m/s^2 at its surface. This value is also the measure of the strength of the gravitational field of the Earth. 

A bonus calculation one can do once we have a value or g is to determine the mass of the Earth! This is because the gravitational acceleration depends on the mass of the planet, g = GM/R^2, where M is the mass of the earth, G is the gravitational constant, and R is the radius of the earth. These values are provided in the lesson plan. 

It is a fascinating idea that the mass of an entire planet can be determined using, effectively, a piece of string!