Sunday, 24 February 2013

Measuring gravity

One of the privileges of working where I do, is that I get the chance to listen to talks/presentations by people who are influential in education.

A while back I was at such a talk, and the speaker was describing an outstanding A-level Physics lesson he had seen. During the lesson the students were split into groups, and each group was using a different method to calculate a value for acceleration due to gravity, g. At the end of the lesson, they discussed all their different values and the teacher helped them to think about the importance of accuracy, repeatability and 'fair testing' that the students had learnt about for many years. However, the need to compare their different values of 'g' meant that they really started to understand the importance of such experimental details, as well as beginning to think about error analysis.

That set me wondering. How many ways are there to measure g that could be done by your average A-level class?

So here are the ones that I have found
  1. Measuring the period of a pendulum
  2. g by freefall using a timer (apparatus can be purchased from most educational suppliers)
  3. g by freefall using lightgates
  4. g by freefall using tickertape and a tickertape timer (word doc)
  5. g ball drop (using a normal ball and timers, using g-ball)
  6. Jump up popper and tracker or audacity
  7. Dropping small masses and recording the sound of them hitting the floor. (I'm in the process of writing a method for this.)
  8. Atwoods machine (never actually seen this done)
  9. Galileo's ramp
There are more than I thought that there would be.  Some of these are variations on a theme, but some of them are quite different.  There's certainly a lot of scope to discuss the accuracy of the different methods, as I suspect that some will give wildly different values of g.
You could also use simulations as well, increasing the number of possible activities or investigations.  The following are all from PhET
Pendulum lab
Mass on a spring
Ramp: Forces and motion

Are there any methods not on here that you use? Do let me know.

Additional reading: Improving science in colleges, Ofsted 2012 (pdf)