Here are two applets students may like to try:
A. The first is a simple “experiment” showing that the extension of a spring is proportional to the force applied:
http://www.absorblearning.com/media/attachment.action?quick=5l&att=394
B. For the second applet, you can try:
- looking for the unknown masses.
- observing the potential energy at different extensions of each spring.
- varying the gravitational field strength.
http://phet.colorado.edu/sims/mass-spring-lab/mass-spring-lab_en.html