Gym Scooter Pulls: Planning a Fair Test of Force and Mass

Sports Science Lab: Scooter Pulls

1During sports science week, Ms. Gwen Takahashi's eighth graders asked why a coach can get a light push sled moving quickly but struggles with a heavy one. Elif Navarro's group decided to test how the net force on an object and the object's mass affect how quickly its speed changes. A heavy sled scrapes on the ground, so the group used a gym scooter board with small wheels instead, loaded with sandbags. Nobody rode on the board, and the sandbags were strapped down so they could not slide off. Before any data were collected, the group wrote down its question, listed what it would change, what it would keep the same and what it would measure, and asked Ms. Takahashi to check that the plan was safe.

2A student pulled the board across the smooth gym floor with a rope attached to a digital force gauge, keeping the gauge reading steady during each run. A motion sensor measured the board's speed. Every run started from rest, so the speed after 1.0 s was also the change in speed during that second. The group used a clear, padded lane, and each run was repeated three times and averaged. For example, the three trials of run 2 gave speeds of 0.9 m/s, 1.0 m/s and 1.1 m/s, so the group recorded 1.0 m/s. Speeds stayed at a walking or jogging pace, and a spotter at the end of the lane caught the board after each run.

3The wheels rub as they roll, so friction pushes back on the moving board. Before the runs, Elif's group pulled each load across the floor at a slow, steady speed and recorded the gauge reading. Those readings are in the friction check table. Then they planned their runs. To test the effect of force, they kept the total mass of the board and sandbags at 20 kg and changed the pull. To test the effect of mass, they changed the number of sandbags and chose each pull so that the net force came out the same. Ms. Takahashi said the results might help the coaches plan training with push sleds, medicine balls and sprint starts.