When a force is applied to a rubber band, it stretches a certain amount. Exactly how much it stretches depends on the applied force and the characteristics of the rubber band. In general, the more force that is applied, the more it stretches. For rubber bands that are not stretched too much, if you double the force applied, it turns out that the stretch doubles as well. Two quantities, x and y, that change in this way are said to be proportional. x and y are related by the constant K in the equation

y = Kx

In this activity you will use a Force Sensor and a Motion Detector to investigate the relationship between the force applied to a rubber band and the distance that the rubber band stretches. To measure how much a rubber band has stretched, we will use the stretched length of the band minus the relaxed length of the band.


  • Record force versus stretch data for a rubber band.
  • Model force versus stretch data with a proportional relationship.