Reaction timer ruler

 

I turned a metre stick into a reaction timer by recalibrating the scale to read in seconds. The idea is that one person holds the ruler vertically level with the top of another person's open hand. When the ruler is dropped, the second person catches it and their reaction time is read from the scale. I used one of the Equations of Uniformly Accelerated Motion to work out the scale division. I used s = ut + 1/2at^2. This reduces to s = 1/2 x g x t^2. Since distance is proportional to t-squared, the linear gaps get bigger.