Grade 12 Physical Sciences - Physics Definitions Guide

Comprehensive vocabulary flashcards covering the official Grade 12 Physical Sciences definitions for Paper 1 (Physics), including Mechanics, Gravitation, Vertical Projectile Motion, Momentum, Work-Energy, Doppler Effect, Electrostatics, Electric Circuits, Electrodynamics, and Optical Phenomena.

Normal force, $N$

The force or the component of a force which a surface exerts on an object with which it is in contact, and which is perpendicular to the surface.

Frictional force, $f$

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

Static frictional force, $f_s$

The force that opposes the tendency of motion of a stationary object relative to a surface.

Kinetic frictional force, $f_k$

The force that opposes the motion of a moving object relative to a surface.

Newton's First Law of Motion

A body will remain in its state of rest or motion at constant velocity unless a non-zero resultant/net force acts on it.

Newton's Second Law of Motion

When a net force acts on an object, the object will accelerate in the direction of the force at an acceleration directly proportional to the force and inversely proportional to the mass of the object.

Newton's Third Law of Motion

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

Newton's Law of Universal Gravitation

Each body in the universe attracts every other body with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centres.

Weight

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

Acceleration

Rate of change of velocity.

Projectile

An object which has been given an initial velocity and then it moves under the influence of the gravitational force only.

Free fall

Motion during which the only force acting on an object is the gravitational force.

Momentum

The product of an object's mass and its velocity.

Newton's Second Law of Motion in terms of momentum

The net (or resultant) force acting on an object is equal to the rate of change of momentum of the object in the direction of the net force.

Impulse

The product of the resultant/net force acting on an object and the time the resultant/net force acts on the object.

Isolated system

A system on which the resultant/net external force is zero.

The Principle of Conservation of Linear Momentum

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

Work done

Work done on an object by a constant force $F$ as $F\,\Delta x\cos(\theta)$, where $F$ is the magnitude of the force, $\Delta x$ the magnitude of the displacement and $\theta$ the angle between the force and the displacement.

Work-energy theorem

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

Conservative force

A force for which the work done in moving an object between two points is independent of the path taken.

Non-conservative force

A force for which the work done in moving an object between two points depends on the path taken.

The Principle of Conservation of Mechanical Energy

The total mechanical energy in an isolated system remains constant. (A system is isolated when the net external force acting on the system is zero).

Power (Work, Energy and Power)

The rate at which work is done or energy is expended.

Doppler Effect

The change in frequency (or pitch) of the sound detected by a listener, because the sound source and the listener have different velocities relative to the medium of sound propagation.

Coulomb's Law

The magnitude of the electrostatic force exerted by one point charge ($Q_1$) on another point charge ($Q_2$) is directly proportional to the product of the magnitudes of the charges and inversely proportional to the square of the distance ($r$) between them.

Electric field

A region of space in which an electric charge experiences a force. The direction of the electric field at a point is the direction that a positive test charge would move if placed at that point.

Electric field at a point

The electric field at a point is the electrostatic force experienced per unit positive charge placed at that point.

Ohm's Law in words

The potential difference across a conductor is directly proportional to the current in the conductor at constant temperature.

Power (Electric Circuits)

The rate at which work is done.

emf

Maximum energy provided by a battery per unit charge passing through it.

Rms potential difference

Is the AC potential difference which dissipates/produces the same amount of energy as an equivalent DC potential difference.

Rms current

Is the alternating current which dissipates/produces the same amount of energy as an equivalent direct current (DC).

Photoelectric effect

The process whereby electrons are ejected from a metal surface when light of suitable frequency is incident on that surface.

Threshold frequency, $f_0$

The minimum frequency of light needed to emit electrons from a certain metal surface.

Work function, $W_0$

The minimum energy that an electron in the metal needs to be emitted from the metal surface.

Atomic absorption spectrum

Is formed when certain frequencies of electromagnetic radiation passing through a substance is absorbed.