Turning Effects of Forces Cambridge (CIE) AS Physics

Vocabulary flashcards covering the concepts of Centre of Gravity, stability, moments, and couples from the Cambridge (CIE) AS Physics syllabus.

Centre of Gravity

The point at which the weight of the object may be considered to act.

Stability

A property of an object determined by the position of its centre of gravity; an object is stable when its centre of gravity lies above its base.

Stable Object Characteristics

An object that has a wide base and a low centre of gravity.

Unstable Object Characteristics

An object that has a narrow base and a high centre of gravity.

Centre of Mass

A point that does not depend on the gravitational field and is usually located at the geometric centre of an object.

Weight Equation

$W = mg$, where $W$ is weight, $m$ is mass, and $g$ is the acceleration due to gravity.

Moment

The turning effect of a force, which occurs when forces cause objects to rotate about a pivot.

Moment Equation

$\text{moment} = Fd$, where $F$ is the force in newtons ($N$) and $d$ is the perpendicular distance from the pivot in metres ($m$).

Newton metres ($N m$)

The unit of measurement for the turning effect of a force (moment) or torque.

Pivot

The point about which an object rotates, such as a hinge in the case of a door.

Couple

A pair of forces that are equal in magnitude, opposite in direction, and perpendicular to the distance between them, acting to produce rotation only.

Resultant force of a couple

A value of zero ($0$), which, according to Newton’s Second law of motion ($F = ma$), means the object does not accelerate.

Torque

The moment of a couple, represented by the Greek letter tau ($\tau$).

Torque Equation

$\tau = Fd$, where $F$ is one of the forces in the couple and $d$ is the perpendicular distance between the forces.

Line of Action

A line through the point at which a force is applied; the forces that make up a couple cannot share the same line of action.