Moment of Force Apparatus

Quick Answer: The Moment of Force Apparatus is a beam-balance set for verifying the principle of moments: a graduated metre rule pivots at its centre on a stand, and movable hangers carry weights at measured distances on either side. Students balance clockwise and anticlockwise turning effects and calculate each moment as force times perpendicular distance.

Turning Effects on a Balanced Metre Rule

A moment is the turning effect of a force about a pivot, found by multiplying the force by the perpendicular distance from the pivot to its line of action. With this moment of force apparatus the pivot is a fulcrum at the middle of a metre rule, so every hanger position can be read straight off the scale. When the rule rests level, the sum of the clockwise moments equals the sum of the anticlockwise moments, which is the principle of moments in its simplest form.

The listing image shows the rule mounted on a pillar with a round base, and weight hangers that slide along the scale on both arms. Because the hangers can be placed anywhere, a class can test several combinations in one lesson: a small load far from the pivot against a larger load close to it, two loads on one side against a single load on the other, or an unknown object balanced against known weights.

The same set-up introduces levers. A fulcrum between effort and load makes a first-class lever, the arrangement found in a see-saw or a pair of scissors, and students can see directly why a long spanner, or a door handle fitted far from the hinge, needs less force. The number of hangers and the weights supplied should be checked when ordering.

Specifications

Applications

• Verifying the principle of moments with two, three or four loads
• Finding the mass of an unknown object by balancing it against known weights
• Locating the centre of gravity of the metre rule itself by balancing it off-centre
• Introductory lessons on first-class levers, see-saws and spanners

Care & Handling

• Check that the unloaded rule sits level before each experiment; a rule that tips on its own adds an unwanted moment to every reading.
• Hang weights gently and steady the rule by hand while adjusting, so the fulcrum edge is not knocked or burred.
• Read hanger positions at eye level, directly above the scale, to avoid parallax errors.
• Store the rule flat or hanging so it cannot warp, and keep the slotted weights together in their box.

Why Choose LabEquip

Science teachers and physics departments buy the moment of force apparatus for the forces and turning-effects unit, often several at once so pairs can work at their own bench. LabEquip supplies it within the STEM kits range as practical mechanics lab equipment, and it pairs naturally with the Moment of Inertia Apparatus when students move on to rotation. Send quantities and delivery details through the contact page.

Frequently Asked Questions

What is the principle of moments?

When an object is balanced about a pivot, the total clockwise moment equals the total anticlockwise moment. Each moment is the force multiplied by its perpendicular distance from the pivot, so a small force far from the pivot can balance a large force close to it.

Why should the rule balance before any weights are hung?

The rule has weight of its own, which acts at its centre of gravity. If that point is exactly over the fulcrum, the rule’s weight has no moment and can be left out of the calculation. If it is off-centre, its moment must be included or the results will not agree.

How can the apparatus find the mass of an unknown object?

Hang the object at a measured distance on one side and move a known weight on the other side until the rule is level. Unknown mass times its distance then equals known mass times its distance, so the unknown mass is the known mass multiplied by the ratio of the two distances.

Is a moment of force the same thing as torque?

Both describe a turning effect and both are measured in newton metres. Moment is the usual term in school statics, where objects are balanced, while torque is more often used for shafts and wheels that rotate, such as an engine crankshaft or a bolt being tightened.

Why are moments measured in newton metres and not joules?

Although a newton metre has the same base units as a joule, a moment is not energy. The distance in a moment is perpendicular to the force and nothing moves through it, so physicists keep the unit written as newton metres to avoid confusion with work done.

What mistakes commonly spoil the readings?

Measuring distances to the end of a hanger instead of to its point of suspension, mixing grams and kilograms between the two sides, and reading the scale at an angle are the usual errors. Taking several balance positions and averaging the results also helps.

Last Updated: September 2026