Grade 12 Physical Sciences Examination Guidelines Vocabulary

Vocabulary definitions extracted directly from the Grade 12 Physical Sciences Examination Guidelines.

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 and the acceleration is 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 ($w$)

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

Momentum ($p$)

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 net force acts on the object.

Isolated system (in Physics)

A system on which the net external force is zero.

Principle of conservation of linear momentum

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

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.

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.

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 ($P$)

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.

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.

emf

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

rms potential difference

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

rms current

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

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

Atomic emission spectrum

Formed when certain frequencies of electromagnetic radiation are emitted due to an atom making a transition from a higher energy state to a lower energy state.

Dipole-dipole forces

Forces between two polar molecules.

Induced dipole forces (London forces)

Forces between non-polar molecules.

Hydrogen bonding

Forces between molecules in which hydrogen is covalently bonded to nitrogen, oxygen or fluorine - a special case of dipole-dipole forces.

Boiling point

The temperature at which the vapour pressure of a substance equals atmospheric pressure.

Melting point

The temperature at which the solid and liquid phases of a substance are at equilibrium.

Vapour pressure

The pressure exerted by a vapour at equilibrium with its liquid in a closed system.

Organic molecules

Molecules containing carbon atoms.

Molecular formula

A chemical formula that indicates the element and numbers of each of the atoms in a molecule.

Structural formula

A structural formula of a compound shows which atoms are attached to which within the molecule, using lines to represent ALL the bonds that hold the atoms together.

Condensed structural formula

Notation showing the way in which atoms are bonded together in the molecule, but DOES NOT SHOW ALL bond lines.

Hydrocarbon

Organic compounds that consist of hydrogen and carbon only.

Homologous series

A series of organic compounds that can be described by the same general formula OR in which one member differs from the next with a $\text{CH}_2$ group.

Saturated compounds

Compounds in which there are no multiple bonds between C atoms in their hydrocarbon chains.

Unsaturated compounds

Compounds with one or more multiple bonds between C atoms in their hydrocarbon chains.

Functional group

A bond or an atom or a group of atoms that determine(s) the physical and chemical properties of a group of organic compounds.

Structural isomer

Organic molecules with the same molecular formula, but different structural formulae.

Chain isomers

Structural isomers with the same molecular formula, but different types of chains.

Positional isomers

Structural isomers with the same molecular formula, but different positions of the side chain, substituents or functional groups on the parent chain.

Functional isomers

Structural isomers with the same molecular formula, but different functional groups.

Heat of reaction ($\Delta H$)

The energy absorbed or released in a chemical reaction.

Exothermic reactions

Reactions that release energy.

Endothermic reactions

Reactions that absorb energy.

Activation energy

The minimum energy needed for a reaction to take place.

Activated complex

The unstable transition state from reactants to products.

Reaction rate

The change in concentration of reactants or products per unit time.

Catalyst

A substance that increases the rate of a chemical reaction without itself undergoing a permanent change.

Reversible reaction

A reaction where products can be converted back to reactants and vice versa.

Chemical equilibrium

A dynamic equilibrium when the rate of the forward reaction equals the rate of the reverse reaction.

Le Chatelier's principle

When the equilibrium in a closed system is disturbed, the system will re-instate a new equilibrium by favouring the reaction that will oppose the disturbance.

Arrhenius acid

Produces hydrogen ions ($\text{H}^+$ / $\text{H}_3\text{O}^+$ / hydronium ions) in aqueous solution.

Arrhenius base

Produces hydroxide ions ($\text{OH}^-$) in aqueous solution.

Lowry-Br(8nsted acid

A proton ($\text{H}^+$ ion) donor.

Lowry-Br(8nsted base

A proton ($\text{H}^+$ ion) acceptor.

Ampholyte

A substance that can act as either acid or base.

Hydrolysis

The reaction of a salt with water.

Equivalence point of a titration

The point at which the acid/base has completely reacted with the base/acid.

Endpoint of a titration

The point where the indicator changes colour.

Galvanic cell

A cell in which chemical energy is converted to electrical energy.

Oxidation

A loss of electrons (or an increase in oxidation number).

Reduction

A gain of electrons (or a decrease in oxidation number).

Oxidising agent

A substance that is reduced / gains electrons.

Reducing agent

A substance that is oxidised / loses electrons.

Anode

The electrode where oxidation takes place.

Cathode

The electrode where reduction takes place.

Electrolyte

A substance of which the aqueous solution contains ions OR a substance that dissolves in water to give a solution that conducts electricity.

Electrolytic cell

A cell in which electrical energy is converted into chemical energy.

Electrolysis

The chemical process in which electrical energy is converted to chemical energy OR the use of electrical energy to produce a chemical change.