Overview
This lecture reviews the core content for AQA GCSE Physics Paper 2, covering Forces, Waves, Magnetism, and Space (Space is triple only), including key concepts, definitions, equations, and practical applications.
Forces and Motion
- A force is any push or pull, which can be contact (objects touch) or non-contact (magnetism, gravity).
- Forces are vectors (have magnitude and direction), represented by arrows.
- Resultant force is the vector sum of all forces acting on an object.
- If forces are balanced (sum to zero), an object moves at constant velocity (Newton's First Law).
- Scalars have only magnitude; vectors have magnitude and direction (e.g. speed is scalar, velocity is vector).
- Weight (force due to gravity) = mass × gravitational field strength (9.8 or 10 N/kg on Earth).
- Work done = force × distance moved (energy transferred by a force).
- For lifting: gain in gravitational potential energy = mass × g × height.
- Hooke's Law: Force on a spring = spring constant (k) × extension (F = kx).
- Energy stored in a spring = 0.5 × k × extension².
- Moment (turning force) = force × perpendicular distance from pivot.
- Pressure = force ÷ area; pressure in fluids = height × density × g.
Kinematics and Dynamics
- Speed = distance ÷ time; velocity includes direction.
- On distance-time graphs: gradient = speed; on velocity-time graphs: gradient = acceleration.
- Acceleration = change in velocity ÷ time; gravity accelerates at 9.8 m/s².
- Equations of motion (suvat) relate displacement, initial/final velocity, acceleration, and time.
- Newton's Second Law: resultant force = mass × acceleration (F = ma).
- Newton's Third Law: every action has an equal and opposite reaction.
- Stopping distance = thinking distance + braking distance; braking distance ∝ (speed)².
- Momentum = mass × velocity; total momentum is conserved in collisions.
- Force = change in momentum ÷ time; safety features increase time to reduce force.
Waves
- Waves transfer energy without transferring matter.
- Longitudinal waves: oscillations parallel to energy transfer (e.g., sound).
- Transverse waves: oscillations perpendicular to energy transfer (e.g., light).
- Amplitude = max displacement; wavelength = distance for one wave cycle; frequency = waves per second (Hz).
- Wave speed = frequency × wavelength (v = fλ).
- Frequency = 1 ÷ time period.
- Reflection: angle in = angle out (measured from normal); smooth = specular, rough = diffuse.
- Refraction is changing direction when entering a new medium due to speed change.
Electromagnetic Spectrum & Applications
- EM waves include radio, micro, IR, visible, UV, X-ray, gamma; higher frequency = more energy, shorter wavelength.
- Some EM waves (UV, X-ray, gamma) can ionise atoms and damage DNA.
- Uses: communication, imaging, heating, medical treatments.
- Visible color depends on reflected/emitted wavelengths; black bodies absorb/emit all wavelengths.
Magnetism and Electromagnetism
- Permanent magnets have aligned domains and produce magnetic fields (lines from North to South pole).
- Induced magnets become magnetised in a field.
- Electric current in a wire produces a magnetic field (circular around wire).
- Motor effect: current in a magnetic field experiences a force (F = BIL, perpendicular only).
- Fleming’s left hand rule shows direction of force, field, and current.
- Electric motors use coils, commutators, and magnetic fields to spin.
- Generator (dynamo) effect: moving a wire in a magnetic field induces a voltage (AC in generators, DC in dynamos).
- Microphones and loudspeakers convert sound waves to/from electrical signals.
Transformers and the National Grid
- Transformers change voltage for transmission; step-up increases voltage (decreases current), step-down lowers voltage.
- Transformer equation: number of turns/voltage ratio is the same (Np/Ns = Vp/Vs).
- Only work with AC; use soft iron cores for efficient magnetic coupling.
Space (Triple Only)
- Solar system: Sun, 8 planets, asteroid belt, natural satellites (moons).
- Stars formed from nebulae; life cycle: main sequence → red giant/supergiant → white/black dwarf or supernova → neutron star/black hole.
- Satellites orbit due to centripetal force; orbits can be circular (geostationary) or elliptical.
- Red-shift in galaxies is evidence for universe expansion and the Big Bang.
- Cosmic Microwave Background Radiation (CMBR) supports the Big Bang theory.
Key Terms & Definitions
- Force — Push or pull on an object.
- Vector — Quantity with magnitude and direction.
- Scalar — Quantity with magnitude only.
- Weight — Force due to gravity (mass × g).
- Moment — Turning effect (force × perpendicular distance).
- Momentum — Product of mass and velocity (kg·m/s).
- Amplitude — Maximum displacement of a wave.
- Wavelength (λ) — Distance for one complete wave cycle.
- Frequency (f) — Number of waves passing per second (Hz).
- EM spectrum — Range of electromagnetic wave frequencies.
- Transformer — Device changing the voltage of AC electricity.
- Red-shift — Increase in wavelength of light from objects moving away.
Action Items / Next Steps
- Review all equations and be able to apply them to problems.
- Practice drawing and interpreting force diagrams and waveforms.
- For triple only: study the space section in detail.
- Complete any assigned homework or exam practice questions on these topics.