For this experiment you need a hard surface that is about 30 cm long and that can be propped up. I used an A4 hard-backed book but if you scroll down, I have some other suggestions of hard surfaces that will work. I found that propping it up at one end with a DVD gave good results. If you prop it up too much the pen will roll too fast to time.
I put a piece of paper on the propped book and drew lines every 5 cm up from the bottom/
I placed a round pen on the 5 cm line and held it in place with a ruler. As I pulled away the ruler, I started my stopwatch with my other hand. I timed it until it reached the bottom of the slope. I did 3 repeats. Obviously the pen or pencil has to be circular. Those hexagonal pencils and pens won't roll properly.
I repeated it for a 10 cm roll, 15 cm, 20 cm and 25 cm.
My whiteboard pen minus lid was also round and would have worked.
I could have used the back of a tray as the hard surface.
Or the kitchen chopping board.
The outside of a folder might work if I could make sure that it wasn't sloping sideways as well.
Look carefully at this picture. There is a little ridge in the paper which meant that my 25 cm results were anomalous. I only noticed when I plotted the graph so I had to repeat that part of the experiment with a properly flat piece of paper. The ridge didn't affect all the results for every distance so it cannot be called a SYSTEMATIC ERROR. Instead, we'll have to call it a RANDOM ERROR.
