Our first real venture into the world of physics begins with a demonstration of a small battery powered buggy. Probably the least exciting demo in science history but the students play along and give me a nice list of observations when asked “What do you notice?” “What can we measure?” And “What can we manipulate?”
Each question is a gentle nudge toward an investigation of the motion of the buggy. Of course at this point, the students are familiar with the relationship of distance and time but I still need to lead them through a discussion of what data should be collected, and how this should be done. Students just want to lay down a meter stick and grab a stop watch and get down to business but I make them wait we have some desicions to make.
Can we just measure time over a single distance and expect our model to be reliable? No we need to clloect multiple trials over multiple distances.
Won’t we all just get the same data? What can we manipulate so that doesn’t happen? They suggest adjusting the carts to move at different speeds. (They don’t know I have already done this.) After much debate we decide it would be more appropriate to keep record of the buggy’s start and stop position rather than how far it has traveled. The students really just gave into me on this part; I am not sure I really convinced them that this would be better. Please leave a comment if you have suggestion for helping them make this decision.
Should we record time over a set distance or record distance over a set time? I did not delve into this discussion. Here, I let them decided to let them decide knowing that the reversed axes on their graphs would lead to some great discussion.
Before class began I taped meter sticks to the lab tables to set individual reference frames for each group. This way I have sown one more difference into their results. Some students end up with graphs that start at zero and end at 200cm, others that start at 200cm and end at 0. Still other’s lines begin at zero and plunge toward -200cm.
These differences in results will help me get at the big concepts related to modeling constant velocity on a motion graph, dependent vs. independent variables, and the importance of a refernce frame. All of theese to be discussed as we study each groups white board in our next session.