Turning effect of forces Flashcards – Cambridge IGCSE (9–1) Physics 0972 (Extended) (2026–2028)

What does the moment of a force measure?

Its turning effect about a pivot.

What equation gives the magnitude of a moment?

$\text{moment} = \text{force} \times \text{perpendicular distance from the pivot}$

How is the perpendicular distance used to calculate a moment measured?

From the pivot to the force’s line of action, at right angles to that line.

What unit is used for moment when force is in newtons and distance is in metres?

Newton metres, $\mathrm{N\,m}$.

What are the two possible directions of a moment?

Clockwise and anticlockwise.

What is the principle of moments?

When there is no resultant moment about a pivot, the total clockwise moment equals the total anticlockwise moment.

For a balanced beam with two forces producing opposite moments, what equation relates the forces and their distances from the pivot?

$F_1d_1 = F_2d_2$, where each distance is perpendicular to the corresponding force’s line of action.

How can a larger force balance a smaller force on a pivoted beam?

The larger force must act at a suitably smaller perpendicular distance from the pivot.

What conditions must the forces and moments on an object satisfy for it to be in equilibrium?

Both the resultant force and the resultant moment must be zero. Neither condition alone is sufficient.

What does zero resultant force mean for an object's centre of mass?

Its centre of mass has no acceleration.

What does zero resultant moment mean for an object's turning motion?

It has no turning acceleration.

How can an object in equilibrium be moving?

It can be stationary or move at constant velocity.