# IGCSE Physics Definitions – Forces and Motion

Last updated on April 12th, 2021 at 09:51 am

**IGCSE Physics Definitions** from the **Forces and Motion** chapter are listed below. It contains definitions for vector, scalar, torque, CG, velocity, force, acceleration, and important laws like Newton’s laws of motion, Hooke’s law, etc.

This post also includes *reference links to detailed posts* on respective topics that would certainly help the students of all boards including **IGCSE** (International General Certificate of Secondary Education), **ICSE**, **CBSE**, **GCSE**, and **Leaving Certificate**.

## IGCSE Physics – Definitions – Forces and Motion

**Scalar** – A scalar is a quantity that has magnitude only.**Vector** – A vector is a quantity that has magnitude and direction. [ Reference: Vector Physics ]

**The moment (or torque) of a force** -The turning effect of a force (or moment or torque) about a point is defined as the force x the perpendicular distance from the point to the line of action of the force, i.e. moment of force or torque = F × d.

UNIT: Nm. [ Reference: Torque ]

**The principle of moments** – For a system to be in equilibrium, the sum of anticlockwise moments about a point = the sum of clockwise moments about the same point. [ Reference: Principle of Moments ]

**Centre of gravity** – The center of gravity is the single point within a body at which the entire weight of the body is considered to act. [ Reference: CG ]

**Displacement** – The displacement of a point B from point A is the shortest distance from A to B, together with the direction.

UNIT: m. [ Reference: displacement ]

**Average speed**Average Speed = total distance traveled ÷ total time taken

UNIT: m/s

[Reference: Average speed]

**Instantaneous SpeedInstantaneous speed is the magnitude of instantaneous velocity and so can never be negative.**

UNIT: m/s.

{Reference: Instantaneous speed]

**Average Velocity**Average velocity = total displacement ÷ total time taken

UNIT: m/s

**Velocity** The velocity of a body is the rate of change of displacement. UNIT: m/s. [by velocity we actually mean instantaneous velocity]

**Instantaneous velocity: **The instantaneous velocity is the ratio of displacement and the time duration provided the time duration is very small (Infinitesimal with time duration approaching zero).

[Reference: Instantaneous Velocity]

**Acceleration**: Acceleration of a body is its rate of change of velocity. UNIT: m/s^2

**Average acceleration** = change in velocity ÷ time taken

UNIT: m/s^2

**Momentum**: The momentum of an object is its mass multiplied by its velocity. (p = mv). It is a vector.

UNIT: kg m/s

[ Reference: Momentum ]

**Newton’s Laws of Motion.****1st Law**

An object continues in a state of uniform motion in a straight line or remains at rest unless acted upon by a resultant

force.**2nd Law**

The rate of change of momentum of an object is proportional to the resultant force acting on it and takes place in the

the direction of that force.**3rd Law**

If an object A exerts a force on a second object B then B must exert a force that is equal in magnitude but opposite in direction on A.

**Elastic collision**: A collision in which there is no loss of kinetic energy. [ Reference: collision ]

**Inelastic collision**. A collision in which kinetic energy is lost. [ Reference: collision ]

**Work**: Work done by a force is the product of the magnitude of the force and the distance moved in the direction of the force

UNIT: joule (J) [= Nm]

[ Reference: Work ]

**Energy**: The energy of a body or system is the amount of work it can do. UNIT: joule (J).

[Ref: Energy ]

**Power**

This is the work done per second, or energy converted or transferred per second.

UNIT: watt (W) [= J/s].

**Law of Conservation of energy** Energy cannot be created or destroyed, only transformed from one form to another.

[ Reference: Law of Conservation of energy]

**Gravitational potential energy**: This is the energy possessed by virtue of position.

Gravitational PE = mgh

{ Reference: Gravitational PE ]

**Terminal Velocity:** The terminal velocity is the constant, maximum velocity of an object when the resistive forces on it are equal and

opposite to the accelerating forces (e.g. pull of gravity).

[ Reference: Terminal Velocity ]

**Extension:**Extension = Stretched length – Original length

**Hooke’s Law**: The extension of an elastic object such as a wire or spring is proportional to the stretching force, provided the extension is not too large. (F = kx).

[Reference: Hooke’s law]

**Spring Constant** The spring constant (k) is the force per unit extension. UNIT: N/m

[ Reference: Spring]

**Efficiency**Efficiency = Useful output work or energy ÷ Input work or energy

## Take Away

Hope this post and all the reference links inside the content would help the global students of **IGCSE** (International General Certificate of Secondary Education), **ICSE**, **CBSE**, **GCSE**, and **Leaving Certificate** to understand the definitions of the Force and Motion chapter in Physics.