Physics: Couples and Centre of Gravity

Vocabulary flashcards covering the concepts of couples, torque calculations, and the definition and properties of the centre of gravity.

Couple

Two equal and opposite parallel forces, not acting along the same line.

Examples of a Couple

Turning a water tap, tightening the cap of an inkpot, turning the key in a hole, and turning a steering wheel.

Torque of a Couple

The product of either force and the perpendicular distance between the two forces, represented as $F \times d$.

Centre of Gravity (Definition 1)

The point about which the algebraic sum of moments of weights of all the particles constituting the body is zero.

Centre of Gravity (Definition 2)

The point where the entire weight of the body can be considered to act, regardless of how the body is placed.

Position of Centre of Gravity

The position of the centre of gravity of a body of given mass depends on its shape, which is determined by the distribution of mass of particles in it.

Centre of Gravity of a Uniform Wire

The centre of gravity of a uniform wire is at the middle of its length.

Centre of Gravity of a Ring

The centre of gravity of a uniform wire bent into a circle is at the centre of the circle.

Material Condition of Centre of Gravity

It is not necessary that the centre of gravity always be within the material of the body; for example, in a ring or hollow sphere, it is at the centre where there is no material.

Balancing a Body

A rigid body can be balanced by supporting it at its centre of gravity.