Finding the strength of Earth's gravitational field (g) and mass with a Pendulum!

Link to Determination of g using a Pendulum lab sheet.  

For a physics class studying anything about gravity, this is a simple and quick experiment that will allow students to determine the acceleration of gravity, g, which is typically 9.8 m/s^2, and is actually the measure of the strength of the gravitational field of the earth, using nothing but a simple pendulum! 

What's more, if you know g, then you can also calculate the mass of the entire planet!! With a piece of string and a little weight tied to the end that can swing! 

Check out this lab. The only materials includes a piece of string and something to tie at the end, perhaps a small stick, or paperclips or a washer. Also a ruler and a way to measure the time it takes the pendulum to swing once back and forth. That time is called the period of the pendulum. The lab gives the formula for the period of the pendulum, and by inserting the length and period time, one can calculate the acceleration due to gravity, g. 

But then we can use the notion from Newton's law of gravity, that g = GM/R^2, where G is the gravitational constant and R is the radius of the earth (given in the lab), and M is the mass of the earth that a student can solve for. Students can get good results to within a few percent if they are careful with their time measurement of the period.