Hooke's Law

Robert Hooke published this law in 1676 as a Latin anagram — ceiiinosssttuv — unscrambled two years later to "ut tensio, sic vis": as the stretch, so the force. An ideal spring pushes or pulls back in proportion to how far you displace it from rest. The spring constant k is the stiffness: a 200 N/m spring stretched 0.1 m pulls back with 20 N, while a car's suspension spring might run tens of thousands of N/m.

This calculator uses the magnitude form; strictly the restoring force points opposite the displacement, which is written F = −kx and is what makes released springs oscillate. The law holds only up to the elastic limit — stretch a spring too far and it deforms permanently. Within that limit it underpins spring scales, force gauges, vehicle suspensions, and even the atomic bonds that make solids springy.