CIE A Level Physics: Turning Effects of Forces in Physics

Centre of Gravity

Point where weight acts on an object.

Stability

Object's resistance to toppling based on center of gravity.

Stable Object

Centre of gravity above its base.

Unstable Object

Centre of gravity not above its base.

Wide Base

Lower centre of gravity increases stability.

Narrow Base

Higher centre of gravity decreases stability.

Centre of Mass

Point representing average position of mass.

Gravitational Field

Region where a mass experiences a force.

Moment

Turning effect produced by a force.

Pivot

Fixed point around which rotation occurs.

Moment Equation

moment = Fd (N m) where F is force.

Perpendicular Distance

Shortest distance from pivot to line of force.

Force at Angle

Use perpendicular component for moment calculation.

Everyday Example of Moments

Opening a door maximizes distance for force.

Turning Moment Calculation

Moment calculated using weight and distance from pivot.

Weight of Ruler

Assumed negligible in moment calculations.

Human Centre of Gravity

Shifts with body orientation and weight distribution.

Symmetrical Objects

Centre of gravity at point of symmetry.

Centre of Gravity in Space

Closer to larger gravitational field object.

Toppling

Occurs when centre of gravity is misaligned with base.

Moment in Newton Metres

Unit of measurement for turning effect.

Force in Newtons

Unit of measurement for applied force.

Distance in Metres

Unit of measurement for distance from pivot.

Force of Weight

Weight calculated as W = mg.

SI Unit of Mass

Mass measured in kilograms (kg).

Weight Calculation

W = 0.5 kg × 9.81 m/s².

Torque

Moment of a couple, τ = Fd.

Couple

Two equal, opposite forces producing rotation.

Resultant Force of a Couple

Zero net force, no acceleration occurs.

Line of Action

Line through the point of force application.

Torque Equation

τ = Fd, where d is perpendicular distance.

Significant Figures

Use more figures to avoid rounding errors.

Turning Effect

Caused by forces acting at a distance.

Torque of Steering Wheel

Calculated using τ = Fd for forces applied.

Ruler Torque Example

Torque calculated with equal forces at ends.

Force Component

Perpendicular component used for torque calculation.

Angle in Torque Calculation

Consider angle to find perpendicular force component.

Torque in Newton Metres

Torque measured in N m.

Diagram Importance

Sketching helps visualize forces and distances.

Force Magnitude

Magnitude of force affects torque value.

Couple Characteristics

Equal forces, opposite directions, perpendicular distance.

Newton's Second Law

F = ma, relates force, mass, and acceleration.

Calculation Rounding

Round final answer, not intermediate results.

Torque Calculation Steps

List quantities, state equation, substitute values.