Measuring force with a spring balance
Hang standard masses on a spring to see how it stretches, then use it as a spring balance to weigh an apple, a stone and a book.
Core concept
A spring stretches in proportion to the force on it, so its stretch can measure force
Topic: Force and motion
A spring stretches when you pull it. Doubling the force: A push or a pull. Forces can start, stop or turn things. All key words 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: The pull that makes things fall towards the Earth. All key words pulls on each kilogram with about 10 N, so a 100 g mass: How much matter something has, measured in grams or kilograms. It is the same everywhere. All key words 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
- Hang 100 g, then 200 g, then 300 g on the soft spring and record the extension each time.
- Hang the apple, the stone and the book and read their weight in newtons.
- 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.