Overview
This lecture covers essential concepts for AQA GCSE Physics Paper 2, focusing on forces, waves, magnetism, and an additional section on space for triple science students.
Forces and Motion
- A force is any push or pull, classified as contact (e.g., friction, tension) or non-contact (e.g., gravity, magnetism).
- Forces are vectors with both magnitude and direction, represented by arrows.
- Resultant force is the vector sum; opposite directions must use negative values.
- If two forces act at right angles, use Pythagoras to find the resultant; use trigonometry (often tan) for angles.
- Balanced forces result in constant velocity (Newton’s First Law).
- Scalars have only magnitude (e.g., speed, distance); vectors have direction (e.g., velocity, displacement).
- Weight is mass × gravitational field strength (g = 9.8 or 10 N/kg on Earth).
- Work done = force × distance; gravitational potential energy (GPE) = mass × g × height.
Deformation and Hooke’s Law
- Hooke’s Law: Force = spring constant (k) × extension; k's unit is N/m.
- Force and extension are directly proportional until the elastic limit.
- Energy stored in a spring: E = ½ × k × extension².
- Extension must be measured accurately to avoid systematic and parallax errors.
Moments, Pressure, and Momentum
- Moment (turning force) = force × perpendicular distance from pivot (unit: Nm).
- Pressure = force/area (unit: Pa), increases with depth (p = h × density × g).
- Atmospheric pressure decreases with altitude.
- Speed = distance/time; velocity includes direction.
- Acceleration = change in velocity/time (unit: m/s²).
- Area under a velocity–time graph gives displacement.
Newton’s Laws and Practical Applications
- Newton's First Law: objects stay at rest or move at constant velocity if forces are balanced (inertia).
- Newton's Second Law: F = m × a.
- Newton's Third Law: every action has an equal and opposite reaction.
- Stopping distance = thinking distance + braking distance; braking distance increases with speed squared.
- Momentum = mass × velocity; total momentum conserved in collisions.
Waves
- Waves transfer energy without transferring matter; oscillations are passed along.
- Longitudinal waves: oscillations parallel (e.g., sound); transverse: oscillations perpendicular (e.g., light).
- Amplitude = max displacement; wavelength (λ); frequency (f, Hz) = 1/time period (T).
- Wave equation: speed (v) = f × λ.
- Reflection: angle of incidence = angle of reflection, measured from the normal.
- Refraction: direction change when light enters a new medium; slows down, bends towards the normal.
Electromagnetic Spectrum and Applications
- EM waves can travel in a vacuum; includes radio, microwave, infrared, visible, UV, X-ray, gamma.
- Higher frequency = higher energy; gamma from nuclei, others from electrons.
- UV, X-rays, gamma can ionize atoms and cause mutations.
- EM waves used for communications, imaging, heating, and treatments.
- Lenses refract light to form images; convex converges, concave diverges.
Magnetism and Electromagnetism
- Permanent magnets have aligned domains; magnetic field lines run N to S.
- Induced magnets temporarily align in a field.
- Current in a wire creates concentric magnetic field lines; right-hand rule for direction.
- The motor effect: force on current-carrying wire in magnetic field (F = BIL if field and current are perpendicular).
- Fleming's left hand rule: predict direction of force.
- Motors use coils and a commutator; increasing current, stronger magnet, or more coil turns increases speed.
- Movement of wire in magnetic field induces a potential (generator effect); AC/alternating current produced.
- Transformers change voltage for efficient electricity transmission (step up for grid, step down for homes).
Space Physics (Triple Only)
- Solar system: Sun, 8 planets, moons, asteroid belt, all orbiting by gravity.
- Stars form from nebulae; life stages: main sequence, red giant/supergiant, white dwarf/black dwarf, supernova, neutron star/black hole.
- Satellites can be natural (moon) or artificial (communication, GPS); geostationary orbit stays over equator.
- Circular motion needs a centripetal force; velocity constantly changes direction.
- Red shift: light from distant galaxies stretched; evidence for expanding universe and Big Bang.
- Cosmic Microwave Background Radiation (CMBR) gives further evidence for Big Bang.
Key Terms & Definitions
- Force — push or pull, measured in newtons (N)
- Vector — quantity with both magnitude and direction
- Scalar — quantity with magnitude only
- Gravitational Field Strength (g) — force per kg (N/kg)
- Moment — turning force, force × distance from pivot
- Pressure — force per unit area (Pa)
- Wave — oscillation that transfers energy
- Amplitude — maximum displacement from rest
- Wavelength (λ) — distance between two identical points of a wave
- Frequency (f) — waves per second (Hz)
- Magnetic Field — region where magnetic forces act
- Motor Effect — force on current-carrying wire in a magnetic field
- Transformer — device changing voltage using electromagnetic induction
- Red Shift — increase in wavelength due to objects moving away
Action Items / Next Steps
- Review and practice key equations (e.g., F = m × a, p = hρg, v = fλ, F = BIL).
- Complete any assigned homework or past paper questions.
- For triple science students, focus additional revision on space physics topics.
- Prepare your own summary notes and flashcards for key terms and equations.