Physics
Spring Constant Mini-Lab
Elastic potential energy is one of the forms of mechanical energy (motion kinetic energy and
gravitational potential energy are the other two forms). Springs store elastic potential energy
when they are compressed and when they are stretched. That energy may be converted into
motion. Your Achilles tendon stores elastic potential energy as well, which is converted back into
kinetic energy when your foot leaves the ground. This reduces your expenditure of metabolic
energy (calories).
In this activity, you will determine the spring constant, which is a measure of the stiffness of a
spring, of two different spring scales. Then you will determine the elastic potential energy stored in
your spring for a certain displacement.
Instructions
1. Stretch the spring scale a certain amount and measure the displacement. Record the
applied to stretch the spring. Repeat for 2 other displacements.
force
2. Repeat step 1 for the second spring scale.
3. Plot force vs. displacement on the graphs below. Include (0,0) on your graph and use a ruler.
Label each line with “tight” and “loose”. Be sure your tick-marks are regularly spaced.
Data
tight spring scale
F (N)
x (cm)
loose spring scale
F (N)
x (cm)
4. Calculate the slope of each line using rise over run. Then write an equation of each line using the
variables in your graph.
Analysis
5. The slope of your line is a ratio of the force to the displacement, which is also known as the
spring constant. Based on your data, what can you generalize about the spring constant of a tight
spring compared to that of a loose spring?
6. What are the units of the slope of your line? These are the units of the spring constant.
Convert your spring constant to N/m, the typical unit for spring constant.
7. Look up the equation for Hooke’s Law (p. 369). How does it compare to the equation of your
lines in #4?
8. Look up the equation for elastic potential energy (Ch. 5). What is the SI unit for energy? Give
two possibilities.
9. Calculate the elastic PE of your tight spring and your loose spring at similar displacements,
using the spring constant in N/m and your spring displacement in m.
10. Summarize what you learned in this activity (at least 2 things).