Measuring 'g'


In this lab, you will measure 'g', the acceleration due to gravity on earth. You will get practice in collecting and interpretting data and estimating uncertainty. You will also use your measurement of g to find the earth's mass.

Suggested Reading

5.1 "Describing Motion: Examples from Daily Life",
5.2 "Newton's Laws of Motion" (AKA "Understanding Motion...")
5.3 "The Force of Gravity",
and 5.6 "The Acceleration of Gravity"




  1. Quantitatively compare your value for g to the current best estimate for the earth's acceleration due to gravity (which you can find in Appendix A of your book). Consider your uncertainty when you compare.
  2. Were there any other sources of error in your estimate of g. besides the uncertainty in t?
  3. Physicists have discovered that the acceleration due to gravity on a planet's surface is related to the planet's mass and radius:

         g = G M / R2

    where G is the gravitational constant (equal to 6.67x10-11 N m2 / kg2), R is the planet's radius and M is its mass. Using the shadows of poles in two different latitudes, someone else has estimated the radius of the earth to be 6.37x106 m. Calculate the mass of the earth.

  4. Use your uncertainty in g to estimate your uncertainty in M.
  5. Quantitatively compare this value to the current best estimate for the earth's mass (also in Appendix A of the book). Consider your uncertainty in M. Does your value match if you include the uncertainty?