Or you could collect and assess the data sheets, including answers to the bonus questions. Or, for an open-ended assessment, try the Astro Ketchup extension below. Answers Conclusions depend on the pens tested, though generally felt-tip will be the clear winners because capillary action keeps the ink flowing through a fibrous core. In the experiment, gravity is still present, working against the action of the pen. Accept reasonable answers, look for mention of the factors listed in the article such as the thickness of the ink and tube, the amount of ink in the tube, capillary action, etc.
Chances are, the students' arms got tired from working against gravity to stay up.
It's important to use three seconds per line to control the variable of time. You could measure results in the amount of time the pen writes for, but you would still need to use the same amount of time per line to control the variable of distance. Design a test to find out. Display the results in a bar graph.