SOUTH AFRICA: Grade 12 CAPS Physics Definitions

Comprehensive vocabulary flashcards covering basic physics principles including mechanics, energy, waves, and electrostatics as per the Grade 12 curriculum.

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.

Weight

The gravitational force the Earth exerts on any object on or near its 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 resultant/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 one body exerts a force on a second body, the second body exerts a force of equal magnitude in the opposite direction on the first body.

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.

Momentum

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

Newton's second law of motion in terms of momentum

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

Impulse-momentum theorem

The theorem represented by the equation $F_{\text{net}} \Delta t = m \Delta v$.

A closed/an isolated system (in Physics)

A system on which the resultant/net external force is zero. It excludes external forces originating outside the colliding bodies (e.g. friction) and considers only internal forces (e.g. contact forces between colliding objects).

The principle of conservation of linear momentum

The total linear momentum of a closed system remains constant (is conserved).

Projectile

An object upon which the only force acting is the force of gravity.

Work ($W$)

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

Work-energy theorem

The net/total work done on an object is equal to the change in the object's kinetic energy ($W_{\text{net}} = \Delta K = K_f - K_i$).

Conservative force

A force for which the work done in moving an object between two points is independent of the path taken, such as gravitational force, elastic force in a spring, or electrostatic forces.

Non-conservative force

A force for which the work done in moving an object between two points depends on the path taken, such as frictional force, air resistance, or tension in a chord.

The principle of conservation of mechanical energy

The total mechanical energy (sum of gravitational potential energy and kinetic energy) in an isolated system remains constant.

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 is that which a positive test charge would move if placed at that point.

The electric field at a point

The electrostatic force experienced per unit positive charge placed at that point.

Ohm's law

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