4.1 AS Level

Turning effects of forces

7 flashcards to master this topic

Definition Flip

Define 'centre of gravity'.

Answer Flip

The centre of gravity is the single point through which the entire weight of an object appears to act, regardless of the object's orientation.

Example: For a uniform sphere, it is at the geometric centre.
Definition Flip

Define the 'moment of a force'.

Answer Flip

The moment of a force is the turning effect of a force about a pivot. It is calculated as the product of the force and the perpendicular distance from the line of action of the force to the pivot: Moment = Force × Perpendicular Distance.

Calculation Flip

State the formula to calculate the moment of a force.

Answer Flip

Moment of a force = Force × Perpendicular Distance from the line of action of the force to the pivot. Units are Newton-metres (Nm).

Definition Flip

What is a 'couple'?

Answer Flip

A couple is a pair of equal and opposite forces acting on a body, but not along the same line. The net force is zero, so it produces rotation only, without translation.

Definition Flip

Define the 'torque of a couple'.

Answer Flip

The torque of a couple is the product of one of the forces and the perpendicular distance between the lines of action of the forces. Torque = Force × Perpendicular Distance.

Calculation Flip

State the formula to calculate the torque of a couple.

Answer Flip

Torque of a couple = Force × Perpendicular Distance between the forces. The unit is the Newton-metre (Nm).

Key Concept Flip

Explain how to determine the centre of gravity of an irregularly shaped object experimentally.

Answer Flip

Suspend the object from a point and hang a plumb line. Draw a line along the plumb line. Repeat from another point. The intersection of the lines indicates the centre of gravity.

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3.3 Linear momentum and its conservation 4.2 Equilibrium of forces