The Bumper and Launcher Kit (BLK) includes two hoop springs, one stiffer than the other.
It is easy to measure the spring constants by placing a Dual-Range Force Sensor (DFS-BTA) in the Bumper Launcher Kit bracket, and a spring on the sensor. Attach the BLK to a Vernier Dynamics Track: Combination Track/Optics Bench (TRACK).
Attach either a Motion Detector (MD-BTD) or the Vernier Motion Encoder System (VDS-EC, discontinued) to measure the position of a cart. While collecting data, press the cart against the spring, recording force and position data.
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.
For the light spring, the slope is about 35 N/m. For the heavy spring, it is about 65 N/m. Spring constants are approximate, as the springs are not designed to be highly consistent.