- reinforce circular motion theory
- practice measuring time period
- use of Excel and LoggerPro
- have fun
Pigs can't really fly, this one hangs from the ceiling from a string. I was lucky to buy the pigs very cheaply but you can use any similar flying toy. The pigs travel quite fast in a fairly big circle so you will need a fair bit of space and some long rulers. The time period is simply measured with a stop watch. In my experience students aren't very good with knots so I tied them all up using a slip not to make changing the length of string easier. I originally used quite long strings but this requires a lot of space and a high mounting point, I later found that a short string (less than 1m) is fine.
The pig needs to be given a push to get it going but once settled it will fly for a long time. Its quite difficult to measure the height from the ceiling, I was quite close to a wall so leaned a long ruler against the wall and moved a horizontal bar up until it was almost touching the pigs feet as it flew past. This worked quite well and gives an easily explained systematic error. An alternative would be to take a photo and analyse with LoggerPro.
Conclusion and Evaluation
I did one measurement for each of 6 lengths and got the following graph
The y intercept is just under 20cm which is due to measuring just under the pigs feet instead of the centre of pig.
From the gradient get a value of 9ms-2 for the acceleration due to gravity which is quite pleasing. Although not shown here the uncertainty in the gradient is about 1cm-2 this gives a maximum value of 9.5ms-2 so a bit low. I won't try to justify my value since my measurements were rather sketchy. I'll wait to see how my students get on before making further comment.