Physics (5th Yr)

Displacement (s)

Distance in a given direction. Unit: metre (m)

Velocity (v)

Rate of change of displacement. Unit: metre per second (m/s)

Acceleration (a)

Rate of change of velocity. Unit: metre per second squared (m/s²)

Force (F)

Anything that tends to move an object and causes acceleration. Unit: newton (N)

Mass (m)

The amount of matter in an object. Unit: kilogram (kg)

Newton’s First Law

An object will remain at rest, or travelling at constant velocity unless acted on by an exterior force

Newton’s Second Law

The rate of change of an object’s momentum is proportional to the force applied (F = ma)

Newton’s Third Law

Every action has an equal and opposite reaction.

F = ma Derivation

1. Force ∝ Rate of change in momentum

2. Force ∝ change in momentum/time

3. Force ∝ mv-mu/t

4. Force ∝ m(v-u/t)

Momentum (p)

Product of mass and velocity. p = mv. Unit: kgms^-1

Principle of Conservation of Momentum

In any interaction between two or more objects, their total momentum before their interactions will equal their total momentum after the interaction, provided no external forces act on the objects

Newton’s Law of Gravitation

The force of gravity between any two objects is

1. proportional to the product of their masses

2. inversely proportional to the distance between them squared

F = Gm₁m₂/d²

Work (W)

When a force moves an object through a distance. Unit: joule (J)

Energy (E)

Ability to do work. Unit: joule (J)

Kinetic Energy (Ek)

Energy due to motion. = ½mv². Unit: joule (J)

Potential Energy (Ep)

Energy due to position. = mgh. Unit: joule (J)

Principle of Conservation of Energy

Energy cannot be created or destroyed, only changed from one form to another.

Power (P)

Rate at which work is done and energy is converted. P = W/t. Unit: watt (W)

Heat

A form of energy due to the motion of molecules. Unit: joule (J)

Temperature (T)

A measure of how hot or cold an object is. Unit: °C or K

Thermometric Property

Physical property that changes measurably with temperature (e.g. length, resistance).

Examples of Thermometers

Mercury thermometer (length), thermistor (resistance), thermocouple (voltage)

Heat Capacity (C)

Heat required to change the temperature of an object by 1°C. Unit: J/°C

Specific Heat Capacity (c)

Heat required to change 1 kg of a substance by 1°C. Unit: J/kg·°C

Latent Heat (L)

Heat needed to change state without changing temperature. Unit: joule (J)

Specific Latent Heat (l)

Heat energy required to change the state of 1 kg of a substance without changing the temperature

Unit: J/kg

Conduction

Heat transfer through solids by particle vibration.

Convection

transfer of heat energy through circulating currents in a fluid

Radiation

Transfer of heat through electromagnetic waves (no medium required).

Reflection

Bouncing of light off a surface.

Incident Ray

Incoming light ray.

Angle of Incidence (i)

Angle between incident ray and normal.

Reflected Ray

Ray that bounces off the surface.

Angle of Reflection (r)

Angle between reflected ray and normal.

Laws of Reflection

1. i = r

2. incident ray, normal and reflected ray lie on the same plane.

Concave Mirror

Converging mirror (curves inward).

Convex Mirror

Diverging mirror (curves outward).

Ray Diagram Components

Principal axis, centre of curvature, focal point, object, image.

Refraction

Bending of light as it passes from one medium to another.

Refracted Ray

Ray that bends in the new medium.

Angle of Refraction (r)

Angle between refracted ray and normal.

Laws of Refraction / Snell’s Law

n = sin i / sin r

Refractive Index (n)

Measure of how much light is bent in a medium.

Apparent Depth

Depth an object appears to be due to refraction; real depth > apparent depth.

Mechanical Wave

Needs a medium (e.g. sound).

Electromagnetic Wave

Doesn’t need a medium (e.g. light).

Transverse Wave

Oscillate perpendicular to wave direction (e.g. light).

Longitudinal Wave

Oscillate parallel to wave direction (e.g. sound).

Amplitude (A)

how high or low the wave goes from its middle/rest position

Wavelength (λ)

Distance between two peaks. Unit: metre (m)

Frequency (f)

Number of waves per second. Unit: hertz (Hz)

Period (T)

Time for one cycle. T = 1/f. Unit: seconds (s)

Reflection in waves

Bouncing back of a wave at a boundary.

Refraction in waves

Bending of a wave at a boundary.

Diffraction

Bending of the wave around an obstacle

Interference

When two waves meet and combine.

Constructive Interference

Waves add to form a larger amplitude.

Destructive Interference

Waves cancel out.

Coherent Sources

Waves with same frequency and constant phase difference.

Polarisation

Filtering waves so they vibrate in one plane only.

Standing/Stationary Wave

Wave that doesn’t appear to travel; nodes and antinodes form.

Node

Point of no displacement.

Antinode

Point of maximum displacement.

Overtone

extra vibration frequencies produced in a string or air column that are multiples of the fundamental frequency

Harmonic

Frequencies at which a system naturally vibrates.

Factors affecting Fundamental Frequency

Length, tension, and mass per unit length of the string.

Sound Characteristics

Pitch (frequency), loudness (amplitude), quality (harmonics).

Light Characteristics

Colour (wavelength), intensity (amplitude), polarisation.

Resonance

The increase in amplitude of an object when driven at its natural frequency by an external force.

Electromagnetic Spectrum

Range of EM waves by frequency.

Dispersion

Separation of light into colours.

Charge by Friction

Rubbing transfers electrons → one becomes positive, one negative.

Charge by Induction

Bringing a charged object near causes redistribution of charges.

Gold Leaf Electroscope

Device used to detect charge and rough size of potential difference

Point Effect

High charge concentration at sharp points → ions escape easily.

Voltage (V)

Potential difference; energy per unit charge. Unit: volt (V)

voltage

Work done moving charge.

EMF (ε)

Energy supplied per unit charge by a source.

Current (I)

Flow of charge. I = Q/t. Unit: ampere (A)

Resistance (R)

acts as opposition to current. V = IR. Unit: ohm (Ω)

Series Circuit

Components connected one after another → same current.

Parallel Circuit

Components connected across same voltage → current splits.

Ohm’s Law

V ∝ I if temperature is constant.

Resistivity (ρ)

Property of material resisting current. Unit: Ω·m

Ring Main Circuit

Domestic wiring loop → multiple sockets.

Radial Circuit

Circuit from fuse board to one appliance.

Light Circuit

Domestic circuit for lighting.

Fuse

Safety device melts if current too high.

MCB

Miniature Circuit Breaker; trips if current too high.

RCD

Residual Current Device; detects current imbalance.

Earthing

Connecting to ground to prevent electric shock.