Measurement of Mass
Simple Explanation
Mass is measured by comparing an unknown mass against known standard masses, using a balance. A beam balance compares two masses directly by seeing when they balance each other; a modern electronic balance instead measures the force needed to support the object and converts that into a mass reading.
Why Do We Need It?
Accurate mass measurement underlies everything from a pharmacy weighing out a precise dose of medicine, to a jeweller weighing gold, to a chemist measuring reactants for an experiment.
Worked Example
Find an unknown mass using a beam balance
A beam balance balances exactly when an object is placed on one pan and standard masses of 200 g, 50 g, and 5 g are placed on the other pan. Find the mass of the object.
Why Does This Work?
A beam balance works by comparing torques (turning effects) on either side of a central pivot — it only settles level when the two masses (and hence the two turning effects) are exactly equal, which is why matching the pans with known masses gives the unknown mass directly.
Real-Life Example
A pharmacy weighing a dose
A pharmacist needs to measure out an exact quantity of a powdered medicine.
A precise balance (traditionally a beam balance, now usually electronic) ensures the patient receives exactly the prescribed dose — a real safety requirement, not just a formality.
Practice
A beam balance balances when an object is compared against standard masses of 100 g, 20 g, and 2 g. Find the mass of the object.
EasyCommon mistake
Confusing mass with weight — mass (measured in kilograms) is the amount of matter in an object and stays the same everywhere, while weight is the force of gravity on that mass and changes from place to place.
Quick Review
- Mass is measured by comparison against known standard masses, using a balance.
- A beam balance compares two masses directly; an electronic balance measures a supporting force.
- Mass (kg) is not the same as weight (a force, in newtons).