How many students does it take....
Today my first year class tried out the balloon drop experiment to find out if a the terminal velocity of a falling balloon is proportional to 1/radius. I gave two options for measuring the terminal velocity, either using a motion sensor or using video analysis. I had originally expected all to use the 3 new vernier motion sensors that I bought from eBay earlier this year, however I over spent my budget and can't afford the power supplies for the labPro interfaces. So, I thought would follow Byron Farrow's suggestion to try video analysis. I was expecting the video to give slightly better results but the velocity time graph did not show any clear terminal velocity so the students decided to use the gradient of the displacement time graph instead. The problem is that if the edge of the balloon is quite indistinct so the points marked on the video with loggerPro tend to jump about a bit, when graphed, this jumping about results in quite big changes of velocity. As you can see in the photo the video method is quite labour intensive, one to stand on the sink to drop the ball, another to pick the ball up and a third (not in the photo) to switch on the video.