The Acceleration of Gravity

In this lab you will measure the acceleration of gravity. It is up to you to come up with the exact way you will do it. Discuss with your partners ways to do it and choose the one method that will get you both an accurate and precise result. As usual, if you require equipment you don’t see, tell me and I’ll try to find something for you.

For the uncertainty, I want you to execute your experiment at least 6 times, so everything you measure must be measured at least 6 times. Each set of measured values will give you a (different) value for g. Average these to get the value you report, and take a standard deviation of these values to get the uncertainty in your reported value.

Does your value agree with the accepted value of 9.8 m/s2? If 9.8 m/s2falls within uncertainty limits of your measured value, then yes it does! For example, if you measure g to be 9.82 ±0.05 m/s2, that means your measured value could be as high as 9.87 or as low as 9.77; 9.8 falls within this range, so your measurement would agree with the accepted value.

Your lab report will include the usual sections:

Name/Partners/Date/Title

Introduction – State the purpose of the experiment.

Theory – Here you need to derive an expression for g in terms of things you will directly measure. You may start with any equation off of our first “cheat sheet”—no need to integrate a constant acceleration to get the 4 kinematics equations. As usual, define all variables.

Experiment – This section must include the usual:

  • Describe how your data was taken. You must include enough information here that 10 years from now, long after you or I have forgotten this experiment, someone else can duplicate your experiment using the same method and equipment. If you are not sure if you should write it down, write it down anyway! You need to especially include little things you did to make your measurements easier, more accurate, or more precise. For this experiment this is especially important, as YOU are designing the experiment! If your method is a poor one or is sloppily executed (e.g., you don’t measure things right), you will get docked.
  • Equipment numbers. If no equipment number exists, a description of brand/model # will suffice.
  • ALL of your data.
  • A diagram/schematic of your experiment.

Analysis – Here you crunch your numbers. Determine the values for g, the average of those values, and the standard deviation in them.

Discussion – Does your measurement of the acceleration agree with the “accepted” value for g? If it does not, then you had better go back and check your measurements and your calculations! If it still doesn’t, then ordinarily I’d tell you to say that the accepted value is wrong. But the value of g has been measured so many times that this is extremely unlikely. Retake your data if necessary. Never turn in a report with flawed data or calculations.

Conclusion–Restate your result (the measured value of g with uncertainty) and either say it agreed (and thus you have confirmed the accepted value of g) or why it didn’t (if your data isn’t flawed!). Again, nothing new should be in the conclusion.

Richard A. Thomas – UST Physics