Know that a deceleration is a negative acceleration and use this in calculations

IGCSE Physics 0625 – Core Topics Overview

1. Motion – Objective (Core 1.2.1)

Know that a deceleration is simply a negative acceleration and be able to use this fact correctly in calculations.

2. Core definitions & symbols (Core 1.2.2)

3. Key kinematic formulas (Core 1.2.3)

• Acceleration: \(\displaystyle \vec{a}= \frac{\Delta\vec{v}}{\Delta t}\)
• Velocity (constant acceleration): \(\displaystyle \vec{v}= \vec{u}+ \vec{a}t\)
• Displacement (constant acceleration): \(\displaystyle \vec{s}= \vec{u}t+\frac{1}{2}\vec{a}t^{2}\)
• Velocity–displacement relation: \(\displaystyle v^{2}=u^{2}+2as\)
• Average speed: \(\displaystyle \bar v =\frac{\text{total distance}}{\text{total time}}\)

Using deceleration in calculations

When an object slows down, its acceleration is negative (a deceleration). In equations simply substitute a negative value for \(\vec{a}\).

Example – A car travelling at 20 m s^‑1 brakes uniformly to rest in 5 s.

1. Identify: \(u = 20\; \text{m s}^{-1},\; v = 0,\; t = 5\; \text{s}\).
2. Find the acceleration: \(\displaystyle a = \frac{v-u}{t}= \frac{0-20}{5}= -4\; \text{m s}^{-2}\). The negative sign indicates deceleration.
3. Find the distance covered while stopping: \(s = ut+\frac12 a t^{2}= 20(5)+\frac12(-4)(5)^{2}=100-50=50\; \text{m}\).

4. Motion – Additional Core Content (1.1, 1.3‑1.7)

4.1 Physical quantities & measurement (1.1)

• Scales, rulers, stop‑watches, digital timers – accuracy & uncertainty.
• Average vs. instantaneous speed/velocity (gradient of a distance‑time graph).

4.2 Forces and Newton’s laws (1.3)

• Resultant force, balanced vs. unbalanced forces.
• Weight \(W = mg\) (g ≈ 9.8 m s^‑2).
• Friction (static & kinetic) and its effect on motion.
• Turning moments: \(M = Fd\).

4.3 Momentum, impulse and conservation (1.4)

• \(\vec{p}=m\vec{v}\); impulse \(\vec{J}=F\Delta t = \Delta\vec{p}\).
• Conservation of momentum in isolated systems (e.g., collisions).

4.4 Work, energy and power (1.5)

• Work \(W = F s \cos\theta\).
• Kinetic energy \(Ek = \frac12 mv^{2}\); gravitational potential energy \(Ep = mgh\).
• Conservation of mechanical energy (neglecting losses).
• Power \(P = \frac{W}{t} = Fv\).

4.5 Energy resources and efficiency (1.6)

• Renewable vs. non‑renewable sources.
• Efficiency \(\displaystyle \eta = \frac{\text{useful energy output}}{\text{total energy input}}\times100\%.\)

4.6 Waves and optics basics (1.7)

• Wave terminology – crest, trough, wavelength \(\lambda\), period \(T\), frequency \(f\).
• Wave speed \(v = f\lambda\).
• Reflection, refraction and the law of reflection.

5. Thermal Physics (Core 2)

• Particle model – matter made of particles in constant motion.
• Temperature scales (Celsius, Kelvin) and conversion \(K = ^\circ\!C + 273\).
• Specific heat capacity: \(Q = mc\Delta T\).
• Phase changes: latent heat of fusion/melting and vaporisation/condensation.
• Heat transfer methods – conduction, convection, radiation.
• Practical example: Calculating the energy required to heat 250 g of water from 20 °C to 80 °C (use \(c_{\text{water}} = 4180\; \text{J kg}^{-1}\!^\circ\!C^{-1}\)).

6. Waves (Core 3)

• Transverse vs. longitudinal waves.
• Wave equation \(v = f\lambda\); use for sound and light.
• Reflection, refraction, diffraction and interference (basic concepts).
• Electromagnetic spectrum – radio, microwaves, infrared, visible, ultraviolet, X‑rays, gamma rays; everyday applications.
• Ray diagrams for mirrors and lenses (concave, convex, converging, diverging).

7. Electricity & Magnetism (Core 4)

7.1 Basic electrical quantities

• Charge \(Q\) (C), current \(I = \frac{\Delta Q}{\Delta t}\) (A), potential difference \(V\) (V), resistance \(R\) (Ω), power \(P = VI\).
• Ohm’s law \(V = IR\); series and parallel circuits.

7.2 Magnetic fields

• Field lines, Earth’s magnetic field, magnetic force on a moving charge \(F = Bqv\sin\theta\).
• Electromagnets and solenoids.

7.3 Electromagnetic induction

• Faraday’s law – induced emf \(\mathcal{E} = -\frac{\Delta\Phi}{\Delta t}\).
• Generators, transformers and the principle of a simple motor.

7.4 Safety

• Fuses, circuit breakers, earthing, RCDs.
• Safe handling of batteries and high‑voltage equipment.

8. Nuclear Physics (Core 5)

• Structure of the atom – protons, neutrons, electrons; isotopes.
• Radioactive decay types: alpha (α), beta (β), gamma (γ).
• Half‑life \(t{1/2}\) and decay law \(N = N0\left(\frac12\right)^{t/t_{1/2}}\).
• Applications: medical imaging, radiocarbon dating, nuclear power.
• Safety: shielding, distance, time.

9. Space Physics (Core 6)

• Earth–Sun–Moon system – rotation, revolution, seasons.
• Orbits – circular approximation, orbital speed \(v = \frac{2\pi r}{T}\).
• Phases of the Moon and eclipses.
• Basic Solar System overview – planets, moons, asteroids, comets.

10. Practical & Experimental Skills (Section 4)

Developing competence in planning, conducting and analysing investigations is essential for AO3 outcomes.

• Measuring g with a simple pendulum (period \(T = 2\pi\sqrt{\frac{L}{g}}\)).
• Determining density by water‑displacement method.
• Investigating the relationship between force, mass and acceleration (Newton’s 2nd law).
• Exploring energy transformations using a roller‑coaster model (potential ↔ kinetic).
• Mapping magnetic field lines with iron filings and a bar magnet.
• Half‑life simulation using a “decay” dice‑roll activity and plotting exponential decay.

11. Summary of the Deceleration Concept

• Deceleration = acceleration with a negative sign.
• Use the same kinematic equations; just insert the negative value for \(\vec{a}\).
• Remember: a negative velocity indicates motion opposite to the chosen positive direction; a negative acceleration indicates the velocity is becoming less positive (or more negative).
• Typical exam question: “A cyclist slows from 12 m s^‑1 to 4 m s^‑1 in 3 s. Calculate the deceleration and the distance covered.” – Apply the formulas above.