Definitions - Topic 1 - Forces and Motion - Edexcel Physics IGCSE

Acceleration

The rate of change of velocity.

Balanced Forces

A resultant force of zero.

Braking Distance

The distance a vehicle travels under the braking force.

Changes of Momentum

Occurs when a force acts on a moving object; force equals the rate of change of momentum.

Conservation of Momentum

The total momentum of a system remains constant before and after an event.

Contact Force

A force that acts on an object through physical contact.

Crumple Zone

A safety feature in vehicles that absorbs energy during a collision.

Distance-Time Graph

A plot showing how an object's distance changes over time.

Distance

A measure of how far an object moves, a scalar quantity.

Distortion

The changing of an object’s size or shape due to a deforming force.

Elastic Deformation

A non-permanent deformation that returns to original shape when forces are removed.

Elastic Limit

The force beyond which an object will deform plastically.

Equilibrium

Condition where resultant force and moment are both equal to zero.

Friction

A resistive contact force that opposes relative motion between surfaces.

Hooke’s Law

Extension of a spring is directly proportional to the applied force within its limits.

Human Reaction Time

The time it takes for the brain to respond to a stimulus.

Limit of Proportionality

Point where the extension of an elastic object is no longer proportional to the applied force.

Linear Relationship

A relationship where an increase in one variable results in a proportional increase in another.

Moment

The turning effect of a force, equal to force times perpendicular distance from pivot.

Momentum

The product of an object's mass and velocity.

Newton Meter

A device used to measure force magnitude.

Newton Metre

The unit of a moment.

Newton

The unit of force.

Newton’s First Law

An object remains at rest or in uniform motion if the resultant force is zero.

Newton’s Second Law

Acceleration is directly proportional to resultant force and inversely proportional to mass.

Newton’s Third Law

Forces exerted by two interacting objects are equal and opposite.

Non-Contact Force

A force acting at a distance without physical contact.

Plastic Deformation

A permanent deformation that does not return to original shape after forces are removed.

Principle of Moments

For equilibrium, the sum of clockwise moments equals the sum of anticlockwise moments.

Resultant Force

The single force that replaces all individual forces acting on an object.

Resultant Moment

The single moment that equals the total of all clockwise and anticlockwise moments.

Scalar Quantities

Quantities that have magnitude only, not direction.

Seat Belt

A vehicle safety device that reduces force experienced by the wearer during a collision.

Spring Constant

A measure of a spring's stiffness.

Stopping Distance

The total of thinking distance and braking distance.

Terminal Velocity

The maximum velocity reached when resistive forces equal weight.

Thinking Distance

The distance a vehicle travels during the driver's reaction time.

Vector Quantities

Quantities with both magnitude and direction, represented by arrows.

Velocity-Time Graph

A plot showing how an object's velocity changes over time.

Velocity

A vector quantity measuring the rate of change of displacement.

Weight

The force acting on an object due to gravity, equal to mass times gravitational field strength.