Hooke's Law Calculator
Free Hooke's law calculator — F = k·x for springs; solve for force, spring constant, or displacement, with elastic energy and an animated spring.
Everyday Uses
Physics homework
Apply F = k·x and find force, spring constant, displacement, or stored energy.
Springs & suspension
Choose or check a spring by the force it produces at a given stretch.
Spring scales
See how a scale turns a spring's stretch into a weight reading.
Catapults & toys
Estimate the launch energy stored in a stretched or compressed spring (½kx²).
Frequently Asked Questions
What is Hooke's law?
Hooke's law states that the force a spring exerts is proportional to how far it is stretched or compressed: F = k × x. Here k is the spring constant (stiffness) in N/m and x is the displacement in metres. A spring with k = 100 N/m stretched 0.2 m pulls back with F = 100 × 0.2 = 20 N.
What is the spring constant?
The spring constant k measures stiffness — the force needed per metre of stretch, in newtons per metre (N/m). A larger k means a stiffer spring. You can find it from k = F ÷ x: if 20 N stretches a spring 0.2 m, then k = 20 ÷ 0.2 = 100 N/m.
How much energy is stored in a stretched spring?
Elastic potential energy is E = ½ × k × x². A spring with k = 100 N/m stretched 0.2 m stores E = ½ × 100 × 0.2² = 2 J. This energy is released when the spring returns to its natural length, which is what launches the object in a catapult or a spring-loaded toy.