Overview
This lecture covers key topics for Edexcel GCSE Physics, including SI units, equations for motion, forces, energy types and transfers, waves, atomic structure, radioactivity, nuclear fission, the solar system, and the universe.
SI Units and Unit Conversions
- SI units are standard measurement units (e.g., seconds for time, meters for distance, kilograms for mass).
- Common prefixes: Giga (10⁹), Mega (10⁶), Kilo (10³), Centi (10⁻²), Milli (10⁻³), Micro (10⁻⁶), Nano (10⁻⁹).
- To convert between units, multiply or divide by the power of ten indicated by the prefixes.
Motion and Graph Analysis
- Distance = Speed × Time; Speed = Distance ÷ Time; Time = Distance ÷ Speed.
- On a distance-time graph, a flat line means stationary; slope = speed.
- Velocity-time graph: acceleration = (final speed - initial speed) ÷ time; area under the graph = distance.
Forces, Mass, and Weight
- Weight = Mass × Gravitational Field Strength.
- Mass is constant, weight varies with gravity.
- Balanced forces mean no change in motion; unbalanced forces cause acceleration.
Types of Forces
- Contact forces: friction, air resistance, normal reaction.
- Non-contact forces: gravity, magnetism, electrostatic.
- Forces are measured in Newtons (N).
Motion and Terminal Velocity
- Terminal velocity is when forces of weight and drag are balanced and an object falls at constant speed.
- Parachutes increase air resistance and reduce terminal velocity.
Circular Motion and Momentum
- Circular motion at constant speed still means changing velocity (direction changes).
- Centripetal force depends on mass, speed, and radius.
- Momentum = Mass × Velocity; conserved in collisions and explosions.
Energy Stores and Transfers
- Types: kinetic, gravitational potential, elastic, nuclear, thermal, magnetic, electrostatic, chemical.
- Energy cannot be created or destroyed, only transferred (conservation of energy).
- Efficiency = (useful energy out ÷ total energy in) × 100%.
Heat Transfer
- Conduction: transfer by particle vibration, best in metals.
- Convection: transfer in liquids/gases by movement of warm fluid.
- Radiation: transfer by electromagnetic waves, affected by surface color.
- Insulation reduces heat loss by conduction, convection, and radiation.
Waves and EM Spectrum
- Transverse waves: vibration perpendicular to wave direction (e.g., light).
- Longitudinal waves: vibration parallel (e.g., sound).
- Wave speed = Frequency × Wavelength.
- EM spectrum in order: radio, microwave, infrared, visible, UV, x-ray, gamma.
Atomic Structure and Radioactivity
- Atom: nucleus (protons+neutrons), electrons orbiting.
- Isotopes: same protons, different neutrons.
- Alpha decay: -2 protons, -2 neutrons; Beta decay: neutron → proton.
- Activity measured in Becquerels (Bq); detected by Geiger counter.
- Half-life: time for half of radioactive nuclei to decay.
Nuclear Fission
- Fission: splitting of a heavy nucleus (e.g., uranium-235), releasing energy, daughter nuclei, and neutrons.
- Chain reactions must be controlled with control rods (absorb neutrons) and moderators (slow neutrons).
- Key risks: radioactive waste, high costs, risk of meltdown.
The Universe and Solar System
- Planets orbit the Sun due to gravity; comets have elliptical orbits.
- Geocentric model (Earth-centered) replaced by heliocentric (Sun-centered) model.
- Universe theories: Big Bang (universe has a beginning) and Steady State (always existed, continuous creation).
- Evidence: redshift (galaxies moving away), cosmic microwave background (CMB) supports the Big Bang.
- Star life cycle: nebula → main sequence → red (super)giant → (supernova → neutron star/black hole) or (white → black dwarf).
Key Terms & Definitions
- SI Unit — standard international unit of measurement.
- Weight — force due to gravity on a mass, measured in Newtons.
- Terminal Velocity — constant speed when drag balances weight.
- Momentum — mass × velocity; conserved in closed systems.
- Half-life — time for half the radioactive atoms to decay.
- Efficiency — ratio of useful energy output to total input.
- Isotope — atoms with same protons, different neutrons.
- Redshift — increase in wavelength as objects move away.
Action Items / Next Steps
- Memorize SI prefixes and their powers of ten.
- Practice using key physics equations (speed, force, energy, waves).
- Review and label energy transfers and Sankey diagrams.
- Complete assigned problem sets and practice past exam questions.