Many schools will have started planning their practical endorsements for their A-level students. Although there is not much new from what we have always been used to do, all exam boards have stressed the importance of practical work, particularly because students will be tested on the skills they will develop through the endorsed practical activities listed in the specifications. Most specs list Free Fall experiments as one of the 6 practicals to do in year 12, so I made the video below using Vernier Video Physics (iOS app). It took us less than 5 minutes to do this and the relatively new feature that allows you to auto track the ball frame by frame lets your students take very precise measurements.
As you can see from the video, the app traces each position of the ball on every frame and it will return various graphs. The y-t graph is very useful, but it is also converted into the graph of its gradient, i.e. the Velocity – Time graph. By measuring the gradient of the slopes at each bounce, students can determine the acceleration of the ball due to gravity and compare their result with g.
The image below shows the Displacement – Time graph.
And this image shows the Velocity – Time graph.
A very quick calculation would show that the change in velocity between 2 and -2 (m/s) is a fairly straight line. The change is (-2 – 2) = -4 m/s. The time interval between these two points is 0.4 s, so g = -4/0.4 = 10 m/s2. (forgive the lack of superscript on the units for acceleration)