A small child can balance a heavier one on a seesaw, simply by sitting further out. That is the moment of a force at work: what turns an object depends not just on how hard you push, but on how far from the pivot you push.
The moment of a force is the force multiplied by the perpendicular distance from the pivot: moment = F × d, in newton metres (N m). For an object in equilibrium, the principle of moments states that the total clockwise moment equals the total anticlockwise moment about any pivot.
The moment of a force is the force multiplied by the perpendicular distance from the pivot to the line of action of the force.
Principle of moments: for a body in equilibrium, the total clockwise moment about a pivot equals the total anticlockwise moment.
Slide the weights along the beam and watch the moments. A small force far from the pivot can balance a large force close to it, because what matters is force times distance, not force alone.
Four quick checks on moments, units, and balancing. Each correct answer earns XP and lights this skill on your star map.
The moment of a force is calculated as...
The unit of a moment is the...
For a balanced beam in equilibrium, the principle of moments states that...
A force of 20 N acts at a perpendicular distance of 0.50 m from a pivot. The moment is...
A uniform plank balances on a central pivot. A 50 N weight sits 0.80 m to the left of the pivot. At what distance to the right must a 40 N weight be placed to keep the plank balanced?
Two traps in one topic. First, a moment uses the perpendicular distance from the pivot to the line of action of the force, not the length of the beam or a slanted distance. Second, balancing moments alone is not full equilibrium. An object is in equilibrium only when there is both no resultant force and no resultant moment. An answer that mentions only one of these is incomplete.
Unlocks once the four checks above are done. Worth more XP, written in the style of Paper 1.
On a seesaw, a child of weight 300 N sits 1.0 m from the pivot. To balance it, a second child sitting 1.5 m from the pivot on the other side must weigh...
A 40 N force acts 0.30 m from a pivot, turning it clockwise. An anticlockwise 30 N force balances it at a distance of...
A beam has equal clockwise and anticlockwise moments about its pivot, but a net sideways force still acts on it. The beam is...
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