Principle of moments: balance a metre rule sim
Slide slotted masses on thread loops along a metre rule on a knife edge until it stays level, read every thread and the pivot off the rule into an empty table, check that clockwise equals anticlockwise moments, weigh a bag of stones, find the rule's own weight by balancing it off centre, plot d against 1/m, and see that a newton-meter pulling at an angle only counts its perpendicular distance.
Turning effect of forces · covers the O-Level, IGCSE, GCSE topic
What the sim shows
Model: moment = force × perpendicular distance from the pivot (N m, distances in m); a rule is balanced when the total clockwise moment equals the total anticlockwise moment, here within 0.002 N m (a chosen limit for a real knife edge). g = 10 N/kg. Wooden metre rule 0 to 100.0 cm, its weight acting at its centre of gravity, the 50.0 cm mark; slotted masses 50 g each on a 50 g hanger; newton-meter 0 to 2.5 N in 0.1 N divisions. Idealised: a friction-free knife edge apart from that limit; a uniform rule that does not bend; threads with no mass; forces on the rule's centre line.
- The metre rule: the part to watch
- Knife edge on a retort stand, slotted masses on hangers, bag of stones, sand tray, newton-meter
Use it in your lessons
- Try it here: anyone can unlock 2 figures free, and a free account unlocks up to 5. Runs on a laptop, a Chromebook or a phone; nothing to install.
- Present it and share student links with the teacher plan, from US$5 a month, billed yearly.
- Put it on your own website or LMS for US$9, paid once, or every sim from US$29 a month.
Free guide: 12 practicals as sims, and how to run one in a lesson →
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