6.1.3—Hooke’s law

For a spring or wire within its proportional region, F=kx: extension x is directly proportional to applied force F.

The relation applies only while the material remains proportional. Use the original length and the extension, not the final length.

If 6 N produces 3 mm extension in the proportional region, 10 N predicts 5 mm for the same spring.

Hooke’s law does not hold indefinitely; crossing the limit of proportionality makes the simple linear relation unreliable.