In our second challenge lab of the semester, students had to predict where a ball would land after rolling off a table, but also predict where to release a battery-powered buggy so that the ball hits the buggy as it drives by.

The setup was that ball first rolled down a brief starter ramp and then went briefly on horizontal track before going off the table. They were not allowed to let the ball roll off the table before the experiment, but they could collect data about the motion of the ball along the horizontal track and motion of the buggy along the floor.

Collecting and Analyzing Data:

5/8 of the groups decided to measure the speed of the ball using a motion detector, where the struggle was to interpret exactly what what the graph was showing and how to get the velocity at the end of the track. S

1/8 of the group used a single photogate setup, where challenge was to align the sensor with the center of the ball so you know the length of travel while in the gate.

2/8 of the groups used a two photogate setup, where the two photogates were set close to each other and students used distance between the gates.

For buggy various groups used motion detector or stopwatches and meter sticks.

Students had about 2 hours to complete the lab, which included time to plan, collect and analyze data, and then make their predictions before observing. Most groups actually hit their buggy, but a few groups only came close. The challenges were:

• Not working diligently enough to get a reliable starting condition to get consistent speed of the edge of the table.
• Not isolating carefully enough the instantaneous speed of the ball (but perhaps an average speed). The ball doesn’t slow much across the track, but enough. One group used a two photo gate setup, but actually used each photogate as a single setup, say that the speed dropped from about 62 cm/s to 58 cm/s. Another groups calculated slope of position vs. time across the first half/ second half and found 58 cm/s vs. 55 cm/s.
• Not working diligent enough to get a good measurement for the time spent on ramp and track. Some groups were so diligent in other areas, but then rushed this part. Often it was the last thing students did, because it dawned on them later that this extra time mattered for knowing where to release the buggy from.

All and all the day was pretty successful. Students were engaged, with many taking different approaches to collecting and analyzing data, identifying and working through different issues that arose for them. Students are getting the hang of being presented challenges, transforming the situation into a problem, and deciding they want to collect data and with what equipment.

On Thursday, we switch to new groups and start our new unit on Forces.