How to use it
- Choose what to find: force, spring constant or extension.
- Enter the two known values and pick their units.
- Read the result in the unit you picked, the energy stored and k in N/m.
Formulas
- Force: F = k × x.
- Spring constant: k = F ÷ x. Extension: x = F ÷ k.
- Elastic energy: E = ½ × k × x², in joules.
Worked example
A spring with k = 200 N/m stretched by 5 cm: F = 200 × 0.05 = 10 N, and it stores ½ × 200 × 0.05² = 0.25 J.
A load of 50 N compresses a spring by 25 mm: k = 50 ÷ 0.025 = 2,000 N/m, which is 2 N/mm, and the stored energy is 0.625 J.
Tips and limits
- Stay in the elastic range. Past the elastic limit the spring deforms permanently and the law no longer holds.
- Measure from rest length. x is the change in length, not the total length of the spring.
- Springs in series and parallel. Two equal springs side by side are twice as stiff; one after the other, half as stiff.