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Measure force · Physics

Force meter

Force meter, with labels: hook to hang it from, spring, scale in N, hook for the load.

What it is for

A force meter (newton meter) measures a force. Its spring stretches more as the pull grows, and a pointer on the spring moves along a scale in newtons; hung upright with a load on its hook, it reads the load’s weight.

Range
0 to 5 N (Practical Test meters: full scale 1.0 N to 3.0 N)
Smallest division
0.1 N
Record to
the nearest 0.1 N, 2.4 N, or, estimating between marks, half a division, 2.45 N; one precision in a table

Why choose it

For a pull you can measure directly: the weight of an object, the force on a trolley, the pull of a string. A top-pan balance measures mass, not force (weight = mass × 9.8 N/kg); choose a force meter whose full scale is just above the largest force, so the reading uses most of the scale.

How to read it

23eye too high:parallax erroreye level:pointer at 2.4 N
  1. Hold it in the direction of the pull: upright to weigh, level to pull sideways.
  2. With nothing on the hook, check the pointer is on 0; adjust it if not.
  3. Hang the load, let it stop bouncing and put your eye level with the pointer.
  4. Read the nearest mark and write the unit: 2.4 N.

Exam-style question

With nothing on the hook, a 0–5 N force meter reads 0.2 N. A student hangs a stone on it without adjusting the zero, and it reads 2.4 N.

  1. What is the weight of the stone?
  2. Calculate the mass of the stone (g = 9.8 N/kg).
  3. Why is this meter a poor choice for a force of 0.3 N?
Show what a good answer says
  1. 2.4 − 0.2 = 2.2 N: the zero error is taken off every reading.
  2. m = W ÷ g = 2.2 ÷ 9.8 = 0.22 kg.
  3. 0.3 N moves the pointer only three small divisions, so the reading is imprecise; a meter with a smaller full scale reads it better.

Teaching points for checking your own answer, not official Cambridge marks.

Common errors

  • Not checking the zero: a pointer at 0.2 N with no load adds 0.2 N to every reading (zero error).
  • Holding it at an angle to the pull, so the spring rubs on the case and reads wrong.
  • Reading from above or below the pointer (parallax error), or while the load is still bouncing.
  • Pulling beyond the end of the scale, which can overstretch the spring for good.

Where you use it here

From the Practical Test apparatus lists of the Cambridge IGCSE Biology 0610, Chemistry 0620 and Physics 0625 syllabuses for 2026–2028, and the apparatus the experiments on this site use.

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