Essential Physics Formulas and Core Principles
Essential Physics Formulas
- Speed = Distance ÷ Time
- Acceleration = (Final Velocity − Initial Velocity) ÷ Time
- Force = Mass × Acceleration
- Weight = Mass × Gravitational Field Strength
- Hooke’s Law: Force = Spring Constant × Extension
- Voltage = Current × Resistance
- Charge = Current × Time
- Energy Transferred = Charge × Voltage
- Wave Speed = Frequency × Wavelength (v = fλ)
- Frequency = 1 ÷ Period
- Refractive Index = sin(i) ÷ sin(r)
- sin(Critical Angle) = 1 ÷ Refractive Index
- Efficiency = (Useful Energy Output ÷ Total Energy Input) × 100%
- Work Done = Force × Distance
- Gravitational Potential Energy = Mass × Gravitational Field Strength × Height
- Kinetic Energy = ½ × Mass × Speed²
- Power = Work Done ÷ Time
- Density = Mass ÷ Volume
Forces, Motion, and Electricity
Forces, Motion, and Electricity: A force can change an object’s speed, direction, or shape. Force, velocity, acceleration, and weight are vectors because they have magnitude and direction, while distance, speed, mass, and energy are scalars because they only have magnitude. Friction opposes motion. Balanced forces produce no change in motion, while unbalanced forces cause acceleration. Terminal velocity occurs when weight equals air resistance. Stopping distance equals thinking distance plus braking distance; it increases with speed, poor road conditions, and slower reaction times.
On a distance-time graph, the gradient equals speed. On a velocity-time graph, the gradient equals acceleration and the area under the graph equals distance travelled. Current is the flow of negatively charged electrons. Voltage is energy transferred per coulomb. In a series circuit, current is the same everywhere and voltage is shared; in a parallel circuit, voltage is the same across each branch and current splits. Current entering a junction equals current leaving it. Higher resistance means lower current. LDRs (Light Dependent Resistors) have lower resistance in bright light, while thermistors have lower resistance at higher temperatures.
Waves and the Electromagnetic Spectrum
Waves, Light, and the Electromagnetic Spectrum: Waves transfer energy without transferring matter. Transverse waves vibrate perpendicular to the direction of travel and include light and electromagnetic waves, while longitudinal waves vibrate parallel to the direction of travel and include sound waves. Amplitude is the maximum displacement from equilibrium, frequency is the number of waves per second, wavelength is the distance between matching points on neighbouring waves, and period is the time for one complete wave.
Reflection occurs when a wave bounces off a surface, and the angle of incidence equals the angle of reflection. Refraction occurs when a wave changes direction entering a different medium. Total internal reflection occurs when light travels from a denser medium to a less dense medium and the angle of incidence exceeds the critical angle; this is used in optical fibres. The electromagnetic spectrum consists of Radio, Microwave, Infrared, Visible, Ultraviolet, X-ray, and Gamma waves. All electromagnetic waves are transverse and travel at the same speed in a vacuum.
- Radio waves: Communication
- Microwaves: Cooking and satellites; can cause internal heating
- Infrared: Heaters; can cause burns
- Visible light: Photography and optical fibres
- Ultraviolet: Fluorescent lamps; can damage skin and eyes
- X-rays: Medical imaging
- Gamma rays: Sterilisation; can cause mutations and cancer
Energy, Density, and Magnetism
Energy and Density: Energy cannot be created or destroyed, only transferred between stores. The main energy stores are chemical, kinetic, gravitational, elastic, thermal, magnetic, electrostatic, and nuclear. Energy can be transferred mechanically, electrically, by heating, or by radiation. Work done equals energy transferred. As an object falls, gravitational potential energy decreases and kinetic energy increases. Thermal energy is transferred by conduction, convection, and radiation.
Conduction occurs mainly in solids. Convection occurs in liquids and gases where warm fluids rise and cool fluids sink. Radiation transfers energy through infrared waves and does not require particles. Heat loss can be reduced using insulation such as double glazing and loft insulation. Density is the amount of mass packed into a volume. Like magnetic poles repel and unlike poles attract. Magnetic field lines travel from north to south, never cross, and are closer together where the field is strongest. Magnetically hard materials are used for permanent magnets, while magnetically soft materials are used in electromagnets. Induced magnetism occurs when a material becomes magnetic because it is placed in a magnetic field.
Key Physics Principles Explained
Acceleration happens when there is a resultant force because unbalanced forces cause a change in motion, while balanced forces mean no acceleration. Terminal velocity occurs when weight = air resistance, so the resultant force becomes zero and the object falls at a constant speed. Current is conserved at a junction because charge can’t be created or destroyed, and voltage is energy transferred per unit charge, so it is shared in series circuits.
Refraction happens because waves change speed when they enter a different medium, causing a change in direction; a higher frequency results in a shorter wavelength because wave speed stays constant. Reflection happens because waves bounce off surfaces, so the angle of incidence = angle of reflection. Total internal reflection occurs when light travels from a denser to less dense medium and the angle is greater than the critical angle, so all light reflects internally.
Practical Experiments and Scientific Units
In Hooke’s Law experiments, you hang masses on a spring, measure extension, and plot force against extension to show F = kx in the straight-line region. In wave experiments, you measure wavelength and frequency and calculate wave speed using v = fλ. In refraction experiments, you shine light through a glass block, trace rays, and measure angles to calculate the refractive index using n = sin(i) / sin(r). In electricity experiments, you vary voltage and measure current to see how resistance changes in components like resistors, lamps, and diodes. In thermal energy experiments, you compare how different materials heat or cool to understand conduction, convection, and radiation.
In all practical questions, you must state independent, dependent, and control variables, repeat readings to improve reliability, and reduce errors such as parallax error, reaction time, and inaccurate measurements. Force, weight, and resultant force are measured in Newtons (N), mass in kilograms (kg), distance in metres (m), time in seconds (s), speed in m/s, acceleration in m/s², energy and work in Joules (J), power in Watts (W), current in Amperes (A), voltage in Volts (V), resistance in Ohms (Ω), frequency in Hertz (Hz), and density in kg/m³.