My demo was rather simple as it consisted of two planks attached to a swivel on a baseboard and whose maximum height could be adjusted, a rubber matt in between and a slew of cylinders:
The first demo is the race. Using a drumstick to make sure that when racing the cylinders, they would be more or less released at the same time, I could show that one cylinder was in fact faster than the other. Mp> The second demo's purpose was to show how to get around measurement issues and how measurements are made. Since I lacked any velocity sensing equipment, I did it the old fashioned way. I measured 25 cm on the board marked it with shiny duct tape and then used my digital camera. By counting the number of frames it took for any cylinder to travel that distance, I was able to more or less figure out the time.