Ramp Lab: Arguing About Gravity at the Skate Park

Ramp Lab Club Notes: Gravity at the Skate Park

1Every Wednesday, the Ramp Lab club meets at the Westbrook skate park, next to the middle school. Members bring their own boards, helmets and pads, and the club keeps a tablet for filming. They skate, film each other and then use the videos to study physics. This month, science teacher Mr. Kwesi Halloran asked eighth graders Mateus Delacroix and Yuki Abernathy to collect evidence about gravity.

2Mateus filmed several runs. A skater who rolls up the curved wall of the quarter-pipe, about 2 m tall, slows down, stops for an instant near the top and rolls back down. A skater who jumps off a ledge comes back down to the ground, and a ball tossed straight up stops and falls back into the skater's hands. Yuki also found a video from a skate park in Australia, on the other side of Earth. The skaters there land back on the ground just like the skaters in Westbrook, even though their "down" points the opposite way in space from ours.

3Next, the club measured how hard Earth pulls on objects at the park. They used a force plate, a flat scale that reads in newtons, and placed each object on it while it was resting. Each object was weighed three times, and the readings matched each time. The readings are in Table 1.

4Then the pair did a drop test. Yuki held the 2.0 kg skateboard and the 0.5 kg helmet side by side, 1.0 m above a soft mat, and let go of both at the same moment. In a slow-motion video, the two objects fell side by side and hit the mat at the same time, about 0.45 s after they were let go. They repeated the drop three times with the same result. Mr. Halloran said that air pushes very little on such heavy, compact objects during a short fall.

5Last, Mr. Halloran used the equation scientists use for gravity to calculate the pull between pairs of skaters standing with their centers 1 m apart. The results are in Table 2. One micronewton (µN) is one millionth of a newton.