Place both ends of the track on a stack of books so that the starting line is higher than the finish line.
Place the wheel on the track and adjust the track’s width so that the zones where the dowel tips begin to narrow are directly on top of the pipe (see photo below). When the track is correctly spaced, tighten the wing nuts to fix it in place.
Release the wheel so it rolls down the track. Make sure it’s centered and will roll on its own with minimal wobble and without being pushed. The wheel should take between twenty and thirty seconds to travel the length of the track. Adjust the height of the track or re-center the wheel as needed.
To begin investigating, position the wheel at the top of the track and let it roll down. What do you notice? How fast do you think it is moving? You can use this relationship to get an estimate:
speed = distance / time
Does the speed of the wheel seem to change as it moves down the track? How can you tell? One way to find out is to use your timer to measure the time it takes to travel the first half of the track and compare it to the time it takes to travel the second half of the track. What do you notice? What do you think would happen if you were to divide the track into quarters? Into eighths?
You can also track the wheel’s position over time. Add a piece of blue painter’s tape to the side of the track, along its whole length. With a permanent marker, indicate the starting point of the wheel (zero seconds). It should line up with the point of the dowel. As the wheel travels down the track, have a partner using a timer shout out “Now!” every two seconds. When he or she does this, place a mark on the blue tape. (You can also use a metronome app to obtain a more consistent time.) Continue this process until the wheel reaches the end of the track (click to enlarge the photo below). What do you notice about the spacing of the marks as the wheel travels down the track?
Cut a new piece of blue tape to match the length of the section of pipe that stretches from the zero-second mark to the first two-second mark. Place this new piece of tape on the left-hand side of the graph. This represents the position of the wheel at two seconds.
Repeat with another new piece of tape that stretches from the zero-second mark to the next two-second mark. Place it on the graph to the right of the first piece of tape. This represents the position of the wheel at four seconds. Repeat this process for each two-second interval, remembering to always begin at the zero-second mark. If the wheel reaches the end of the track before the end of a two-second interval, don’t use that data point.
Look at the completed graph and consider what it represents. Do you notice a pattern? Does any of the data seem to defy the pattern? What do you think you should label the x-axis? The y-axis? What should be the title of your graph? What does this graph tell you about the speed of the wheel as it moves down the ramp?
To further investigate how the speed of the wheel changes over time, create a second graph showing the distance traveled within each two-second time increment.
Return to the tape you originally marked on the track. Look at the first two-second interval and, with your scissors, cut it off at the first two-second mark. This represents the distance the wheel traveled in the time interval between zero and two seconds. Remove this tape and place it on a new graph. Now cut off the tape that represents the distance traveled in the next two-second interval (from two to four seconds) and place it to the right of the first piece on the graph. Continue this process to the end of the tape. If the wheel stopped before the end of a two-second interval, do not use that data point.
Look at the completed graph and consider what this graph represents. What do you notice? Is there a pattern? What does this suggest about the wheel’s speed and how the speed is changing as it moves down the ramp? Does any data seem to defy the pattern? How would you label the x-axis and the y-axis for this graph? How would you title the graph?