Springs can be made from wire! This might actually be really good - get kids to make their own springs, then calculate the spring constant of them.
http://www.instructables.com/id/Make-your-own-springs-in-seconds/step2/expansion-springs/ ← if you happen to have a power tool around
Design Jig to make springs. Different sized tubes, different stiffnesses of wire, different lengths. Wind them! Then have a chart with weights on it to test the stiffness.
Test in compression or extension? Or both?
Compression:
Design (separate for extension/compression?) Ball shooter? Small tubes, strings. Fire things! Shoot things!
Extension:
Catapult? Conservation of momentum.
Draw force diagrams (introduce force diagrams). This is the simplest force diagram!
F = -kx
Get them to measure the spring constants of their own springs.
Concepts of energy being stored in a spring. SPRINGBACK. If you push it down, it holds the energy, then releases it. Can use the mini-catapult as an example for this.
Discuss how springs are used. In cars, e.g., for suspension.
Activities:
Build little catapults! With tubes. For firing marbles around. Give each group a selection of materials, get em to figure out a design.
F= ma with the catapults. Get the students to calculate the force on their spring, how much it goes, then how far their marble will fly. (or bolt, or whatever. How heavy is their marble?)
Buy wire! Different types. Make springs out of it.
Make little catapults out of it!
Note: can refer back to “finding materials” for precision weights.