Grade 9 Physics ALL

Distance-time graph

A graph showing how distance varies with time; the gradient represents speed.

Average speed formula

Average speed = distance moved / time taken

Acceleration formula

Acceleration = change in velocity / time taken

Velocity-time graph

A graph showing how velocity varies with time; the gradient represents acceleration.

Acceleration from velocity-time graph

Determined by the gradient of the graph.

Distance from velocity-time graph

Determined by the area under the graph.

Final speed formula

v² = u² + 2as

Effects of forces

Forces can change the speed

Types of forces

Gravitational

Vector vs scalar quantities

Vectors have magnitude and direction; scalars have magnitude only.

Force as a vector quantity

Force has both magnitude and direction

Resultant force

The single force that has the same effect as all the individual forces acting together.

Friction

A force that opposes motion between two surfaces in contact.

Newton's Second Law

Force = mass × acceleration (F = m × a)

Weight formula

Weight = mass × gravitational field strength (W = m × g)

Centre of gravity

The point through which the weight of a body acts.

Newton's Third Law

For every action

Stopping distance

The sum of the thinking distance and the braking distance.

Factors affecting stopping distance

Speed

Forces on falling objects

Weight acts downwards; air resistance acts upwards; terminal velocity is reached when these forces balance.

Hooke's Law

The extension of a spring is directly proportional to the force applied

Elastic behaviour

The ability of a material to return to its original shape after the force is removed.

Momentum formula

Momentum = mass × velocity (p = m × v)

Conservation of momentum

In a closed system

Force and momentum change

Force = change in momentum / time taken (F = (mv - mu) / t)

Moment of a force

Moment = force × perpendicular distance from the pivot

Principle of moments

For an object in equilibrium

Upward forces on a beam

Vary depending on the position of a heavy object placed on the beam.

Energy stores

Chemical

Energy transfer methods

Mechanically

Conservation of energy

Energy cannot be created or destroyed

Efficiency formula

Efficiency (%) = (useful energy output / total energy input) × 100

Sankey diagrams

Diagrams that show energy input

Thermal energy transfer methods

Conduction

Convection in everyday phenomena

Movement of warm fluids rising and cool fluids sinking

Radiation and surface temperature

Dark

Reducing unwanted energy transfer

Using insulation

Work done formula

Work done = force × distance moved in the direction of the force (W = F × d)

Work and energy transfer

Work done is equal to energy transferred.

Gravitational potential energy formula

GPE = mass × gravitational field strength × height (GPE = m × g × h)

Kinetic energy formula

KE = 0.5 × mass × speed² (KE = ½ × m × v²)

Energy conservation link

In a closed system

Power definition

Power is the rate of transfer of energy or the rate of doing work.

Power formula

Power = work done / time taken (P = W / t)

Energy resources for electricity generation

Wind

Advantages of renewable resources

Sustainable

Disadvantages of renewable resources

Intermittent supply

Structure of an atom

Consists of protons

Atomic number

The number of protons in an atom's nucleus.

Mass number

The total number of protons and neutrons in an atom's nucleus.

Isotopes

Atoms of the same element with different numbers of neutrons.

Types of ionising radiation

Alpha particles

Properties of alpha radiation

Low penetration

Properties of beta radiation

Medium penetration

Properties of gamma radiation

High penetration

Detecting radiation

Using photographic film or a Geiger–Müller detector.

Background radiation sources

Natural sources (e.g.

Activity of a radioactive source

The rate at which a radioactive source decays

Half-life

The time taken for half the nuclei in a radioactive sample to decay.

Uses of radioactivity

Medical imaging

Contamination vs irradiation

Contamination is the presence of radioactive material; irradiation is exposure to radiation.

Dangers of ionising radiation

Can cause mutations

Nuclear fission

The splitting of a heavy nucleus into two lighter nuclei

Chain reaction

A self-sustaining series of nuclear fissions.

Control rods in reactors

Absorb neutrons to control the rate of fission.

Moderator in reactors

Slows down neutrons to sustain the chain reaction.

Shielding in reactors

Protects against radiation by absorbing it.

Nuclear fusion

The joining of two light nuclei to form a heavier nucleus

Fusion in stars

Stars produce energy through nuclear fusion of hydrogen into helium.

Conditions for fusion

Requires high temperatures and pressures to overcome electrostatic repulsion.

Universe composition

A vast collection of billions of galaxies.

Galaxy definition

A large collection of billions of stars.

Milky Way

The galaxy that contains our solar system.

Gravitational field strength variation

Varies depending on the mass of the object and distance from it.

Gravitational force effects

Causes moons to orbit planets

Orbital differences

Comets have elliptical orbits; planets and moons have more circular orbits.

Orbital speed formula

Orbital speed = 2 × π × orbital radius / time period

Star classification by colour

Based on surface temperature; blue is hottest

Star evolution (sun-like)

Nebula → main sequence star → red giant → white dwarf.

Star evolution (massive)

Nebula → main sequence star → red supergiant → supernova → neutron star or black hole.

Absolute magnitude

A measure of a star's brightness at a standard distance.

Hertzsprung–Russell diagram

A graph plotting stars' luminosity against their temperature.

Big Bang theory

The theory that the universe began from a single point and has been expanding.

Evidence for Big Bang

Red-shift of galaxies and cosmic microwave background radiation.

Red-shift

The increase in wavelength of light from galaxies moving away from us.

Red-shift equation

(Change in wavelength / reference wavelength) = velocity of galaxy / speed of light

Term

Definition

Types of ionising radiation

Alpha (α)

Alpha particle composition

2 protons and 2 neutrons (Helium nucleus)

Beta particle composition

A high-speed electron (β-) or positron (β+)

Gamma ray composition

Electromagnetic wave (high-frequency photon)

Alpha radiation penetration

Very low – stopped by paper or skin

Beta radiation penetration

Medium – stopped by a few mm of aluminium

Gamma radiation penetration

Very high – reduced by thick lead or concrete

Alpha ionising ability

Very strong ioniser

Beta ionising ability

Moderate ioniser

Gamma ionising ability

Weak ioniser

Speed of alpha particles

Slow – about 10% the speed of light

Speed of beta particles

Fast – close to the speed of light

Speed of gamma rays

Speed of light (3 × 10⁸ m/s)