Hooke's Law, Moments, and Momentum

Ever wondered why springs bounce back or how a small person can lift something heavy with a lever? Hooke's Law explains that when you stretch a spring, the extension is directly proportional to the force you apply. The formula is simple: Force = Spring constant × extension.

This relationship only works until you reach the elastic limit - the point where the spring can't bounce back to its original shape. On a force-extension graph, Hooke's Law applies during the straight line portion, but when the line starts to curve, you've pushed the spring too far.

Moments are all about the turning effect of forces around a pivot point. Think of using a spanner or opening a door - the further from the pivot you apply force, the easier it becomes. The formula is Moment = Force × perpendicular distance from pivot. When something is balanced, the clockwise moments equal the anticlockwise moments.

Momentum measures how hard it is to stop a moving object. Calculate it using Momentum = mass × velocity. A heavy lorry moving fast has massive momentum, whilst a tennis ball has very little. The key principle is that momentum is conserved - the total momentum before a collision equals the total momentum after.

Quick Tip: Remember that momentum is a vector quantity because velocity is a vector - direction matters!

Newton's second law connects force to momentum changes: Force = change in momentum ÷ time taken. Car safety features like seatbelts, airbags, and crumple zones all work by increasing the time it takes to stop, which reduces the force on passengers during crashes.