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Grade 8 Beginner About 15 min Version 1 Awaiting review Premium

Measuring force with a spring balance

A spring stretches when you pull it. Doubling the force doubles the stretch (the extension), as long as you do not overstretch the spring. This is Hooke's law. A spring balance uses this idea: a spring inside a tube stretches as an object pulls on it, and a pointer moves along a scale marked in newtons (N). On Earth, gravity pulls on each kilogram with about 10 N, so a 100 g mass weighs about 1 N. A stiffer spring stretches less for the same force, so it can measure bigger forces.

What you will learn

  • Read a force in newtons from a spring balance.
  • Show that the extension of a spring is proportional to the force on it.
  • Compare a soft spring and a stiff spring.

Before you start

  • Know that weight is the pull of gravity on an object.

Materials

  • Slotted masses of 100 g
  • An apple, a stone and a book

Equipment

  • Soft and stiff springs, or two spring balances
  • Clamp stand and a ruler

Procedure

  1. Hang 100 g, then 200 g, then 300 g on the soft spring and record the extension each time.
  2. Hang the apple, the stone and the book and read their weight in newtons.
  3. Change to the stiff spring, hang the same object and compare the stretch.

How this simulation is simplified

  • g is taken as 10 N/kg, so 100 g weighs 1 N.
  • The springs are never stretched past their elastic limit.