spring balance

A spring balance is an instrument that measures force or weight by measuring how much a spring stretches.

• It usually has a hook at the bottom for hanging an object and a scale marked in newtons (N).
• When an object is hung from it, Earth pulls the object downward. The object pulls on the spring, making it stretch.
• A heavier object produces a greater pull, so the spring stretches farther. The pointer moves along the scale to show the object’s weight.
• Think of it like a stretchy rubber band: a light keychain stretches it only a little, while a filled water bottle stretches it much more. A spring balance uses a carefully made spring so that each amount of stretch matches a particular force.
• For an accurate reading, hold the balance vertically, wait until the pointer becomes still, and read the scale at eye level. Never hang an object heavier than its maximum range, as this can damage the spring.

A spring balance measures weight, which is a force—not mass. Its reading may change on the Moon or another planet because gravity is different there.