IGCSE Physics Definitions
1. Forces and Motion
Scalar
A scalar is a quantity that has magnitude only.
Vector
A vector is a quantity that has magnitude and direction.
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 = F × d. UNIT: Nm.
The principle of moments
For a system to be in equilibrium, sum of anticlockwise moments about a point = sum of clockwise moments about the same point.
Centre of gravity
The centre of gravity is the single point within a body at which the entire weight of the body is considered to act.
Displacement
The displacement of a point B from a point A is the shortest distance from A to B, together with the direction. UNIT: m.
Average speed
Average Speed =
total distance travelled ÷ total time taken UNIT: m/s
Instantaneous Speed
instantaneous speed = rate of change of distance UNIT: ms-1.
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
Average acceleration
= change in velocity ÷ time taken
UNIT: m/s2
Acceleration
Acceleration of a body is its rate of change of velocity. UNIT: m/s2
Momentum
The momentum of an object is its mass multiplied by its velocity. (p = mv). It is a vector.
UNIT: kg m/s
, 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 direction of
that force.
3rd Law
If an object A exerts a force on a second object B then B must exert a force which is equal in magnitude but opposite in direction on
A.
Elastic collision
A collision in which there is no loss of kinetic energy.
Inelastic collision.A collision in which kinetic energy is lost.
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]
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).
EnergyThe energy of a body or system is the amount of work it can do. UNIT: joule (J).
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.
Gravitational potential energy
This is energy possessed by virtue of position.
Gravitational PE = mgh
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).
Extension
Extension = Stretched length – Original length
Hooke’s Law
1. Forces and Motion
Scalar
A scalar is a quantity that has magnitude only.
Vector
A vector is a quantity that has magnitude and direction.
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 = F × d. UNIT: Nm.
The principle of moments
For a system to be in equilibrium, sum of anticlockwise moments about a point = sum of clockwise moments about the same point.
Centre of gravity
The centre of gravity is the single point within a body at which the entire weight of the body is considered to act.
Displacement
The displacement of a point B from a point A is the shortest distance from A to B, together with the direction. UNIT: m.
Average speed
Average Speed =
total distance travelled ÷ total time taken UNIT: m/s
Instantaneous Speed
instantaneous speed = rate of change of distance UNIT: ms-1.
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
Average acceleration
= change in velocity ÷ time taken
UNIT: m/s2
Acceleration
Acceleration of a body is its rate of change of velocity. UNIT: m/s2
Momentum
The momentum of an object is its mass multiplied by its velocity. (p = mv). It is a vector.
UNIT: kg m/s
, 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 direction of
that force.
3rd Law
If an object A exerts a force on a second object B then B must exert a force which is equal in magnitude but opposite in direction on
A.
Elastic collision
A collision in which there is no loss of kinetic energy.
Inelastic collision.A collision in which kinetic energy is lost.
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]
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).
EnergyThe energy of a body or system is the amount of work it can do. UNIT: joule (J).
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.
Gravitational potential energy
This is energy possessed by virtue of position.
Gravitational PE = mgh
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).
Extension
Extension = Stretched length – Original length
Hooke’s Law
