# IEB Matric Physics Definitions

Vector

A physical quantity that has both magnitude and direction.

Scalar

A physical quantity that has magnitude only.

Resultant vector

The single vector which has the same effect as the original vectors acting together.

Distance

The length of path travelled. Distance is a scalar quantity.

Displacement

A change in position.

Speed

The rate of change of distance. Speed is a scalar quantity.

Velocity

The rate of change of position (or displacement). Velocity is a vector quantity.

Acceleration

The rate of change of velocity.

Weight (Fg)

The gravitational force the Earth exerts on any object on or near its surface.

Normal force (FN)

The perpendicular force exerted by a surface on an object in contact with it.

Frictional force due to a surface (Ff)

The force that opposes the motion of an object and acts parallel to the surface with which the object is in contact.

Newton's first law

An object continues in a state of rest or uniform (moving with constant) velocity unless it is acted upon by a net or resultant force.

Inertia

The property of an object that causes it to resist a change in its state of rest or uniform motion.

Newton's second law

When a net force, Fnet, is applied to an object of mass, m, it accelerates in the direction of the net force. The acceleration, a, is directly proportional to the net force and inversely proportional to the mass.

Newton's third law

When object A exerts a force on object B, object B simultaneously exerts an oppositely directed force of equal magnitude on object A.

Momentum

The product of the mass and velocity of the object.

Newton's second law in terms of momentum

The net force acting on an object is equal to the rate of change of momentum.

Law of conservation of linear momentum

The total linear momentum of an isolated system remains constant (is conserved).

Elastic collision

A collision in which both momentum and kinetic energy are conserved.

Inelastic collision

A collision in which only momentum is conserved.

Impulse

The product of the net force and the contact time.

Work done on an object by a force

The product of the displacement and the component of the force parallel to the displacement.

Gravitational potential energy

The energy a object possesses due to its position relative to a reference point.

Kinetic energy

The energy an object has as a result of the object's motion.

Mechanical energy

The sum of gravitational potential and kinetic energy at a point.

Law of conservation of energy

The total energy in a system cannot be created nor destroyed; only transferred from one form to another.

Principle of conservation of mechanical energy

In the absence of air resistance or any external forces, the mechanical energy of an object is constant.

The work-energy theorem

The work done by a net force on an object is equal to the change in kinetic energy of the object

Power

The rate at which work is done, or the rate at which energy is transferred.

One watt

The power when one joule of work is done in one second

Efficiency

The ratio of output power to input power

Newton's law of universal gravitation

Every particle in the universe attracts every other particle with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centres

Coulomb's law

The force between two charges is directly proportional to the product of the charges and inversely proportional to the distance between the charges squared.

Magnitude of the electric field at a point

The force per unit positive charge.

Potential difference

The work done per unit positive charge.

Current

The rate of flow of charge.

Ohm's law

Current through a conductor is directly proportional to the potential difference across the conductor at constant temperature.

Resistance

A material's opposition to the flow of electric current.

Emf

The total energy supplied per coulomb of charge by the cell.

Magnetic flux density (B)

A representation of the magnitude and direction of the magnetic field.

The product of the number of turns on the coil and the flux through the coil.

The emf induced is directly proportional to the rate of change of magnetic flux (flux linkage).

Lenz's law

The induced current flows in a direction so as to set up a magnetic field to oppose the change in magnetic flux.

Diode

A component that only allows current to flow in one direction.

Threshold (cut-off) frequency (fo)

The minimum frequency of incident radiation at which electrons will be emitted from a particular metal.

Work function (Wo)

The minimum amount of energy needed to emit an electron from the surface of a metal. Work function if material specific.