The Bumper and Launcher Kit (BLK) and Go Direct® Sensor Cart Accessory Kit (GDX-CART-AK) include two hoop springs, one stiffer than the other. 

The spring constants for these units are not a specified parameter. There is significant variation due to the source of the spring steel used in any given era of manufacture. If you require accurate values for lab experiments, you or your students should determine the spring constant experimentally. You can measure the spring constants using force sensors. Below are instructions for doing so.

Using the Bumper Launcher Kit

  • Place a Dual-Range Force Sensor (DFS-BTA) or Go Direct® Force and Acceleration Sensor (GDX-FOR) in the Bumper Launcher Kit bracket.
  • Attach a Hoop Spring to the force sensor, then attach the Bumper Launcher Kit Bracket to a Combination Track/Optics Bench (TRACK).
  • Use one of the following options to measure the distance the spring is compressed:
  • While collecting data, press the cart against the spring, recording force and position data. Be careful not to compress the hoop spring more than half its diameter or you may permanently deform the spring.
  • Graph Force vs Position, and select only the portion of the data corresponding to the cart in contact with the spring. This section will be nearly linear.
  • Use a linear curve fit of the selected region to determine the spring constant. The slope of the linear fit represents the spring constant.

Using a Go Direct Sensor Cart

  • Attach a Hoop Spring to the force sensor on a Go Direct® Sensor Cart (GDX-CART-G).
  • Attach an Adjustable End Stop (AS-VDS) to a Combination Track/Optics Bench (TRACK).
  • Connect the Go Direct Sensor Cart to your computing device and set the Sensor Channels to include both Position and Force.
  • While collecting data, press the cart’s spring against the end stop. Be careful not to compress the hoop spring more than half its diameter or you may permanently deform the spring.
  • Graph Force vs Position, and select only the portion of the data corresponding to the spring in contact with the end stop. This section will be nearly linear.
  • Use a linear curve fit of the selected region to determine the spring constant. The slope of the linear fit represents the spring constant.