Physics Basics – Study Notes
(APO Exam – General Awareness & Current Affairs)
1. Simple Explanation
Physics is the science that studies matter, energy, space, and time. It seeks to explain how the universe behaves through laws, principles, and mathematical relationships.
Key ideas:
| Concept | What it means | Everyday example |
|---|---|---|
| Force | Push or pull that changes motion | Opening a door |
| Motion | Change in position over time | A car accelerating |
| Energy | Ability to do work | A battery powering a light |
| Momentum | Product of mass and velocity | A moving train |
| Work | Force applied through a distance | Lifting a box |
| Power | Work done per unit time | A 100 W lightbulb |
2. Key Points
| Category | Important Points |
|---|---|
| Newton’s Laws of Motion | 1️⃣ Inertia – objects stay at rest or move uniformly unless acted on. 2️⃣ F = ma – force equals mass times acceleration. 3️⃣ Action‑reaction – forces come in equal and opposite pairs. |
| Kinematics | Describes motion without forces. Equations: • (v = u + at) (velocity) • (s = ut + \tfrac{1}{2}at^2) (displacement) • (v^2 = u^2 + 2as) |
| Energy Types | Kinetic (moving), Potential (stored). Conservation: total energy remains constant (ignoring friction). |
| Work & Power | Work: (W = F \times d \times \cos\theta) Power: (P = W/t) |
| Momentum & Collisions | Momentum: (p = mv) Elastic collision: both kinetic energy & momentum conserved. |
| Gravity | Universal law: (F = G\frac{m_1m_2}{r^2}). Near Earth: (F = mg). |
| Electricity (Basic) | Current (I = Q/t). Voltage (V = IR). Power (P = VI). |
| Wave Properties | Wavelength (\lambda), frequency (f), speed (c = \lambda f). |
| Thermodynamics | Laws: 1st (energy conservation), 2nd (entropy increases), 3rd (entropy → 0 at 0 K). |
3. Worked Example
Problem:
A 5 kg cart is pulled by a constant horizontal force of 20 N across a frictionless table.
Find:
- Acceleration of the cart.
- Displacement after 4 s if it starts from rest.
Solution
-
Acceleration (Newton’s 2nd Law)
[ F = ma ;\Rightarrow; a = \frac{F}{m} = \frac{20,\text{N}}{5,\text{kg}} = 4,\text{m/s}^2 ] -
Displacement (Kinematics)
Initial velocity (u = 0).
[ s = ut + \tfrac12 at^2 = 0 + \tfrac12(4)(4^2) = 0.5 \times 4 \times 16 = 32,\text{m} ]
Answer:
- Acceleration = 4 m/s²
- Displacement after 4 s = 32 m
4. Quick Revision Summary
| Topic | Flash‑card |
|---|---|
| Newton’s 1st Law | Inertia – “Objects resist changes in motion.” |
| Newton’s 2nd Law | (F = ma) – Force is mass times acceleration. |
| Newton’s 3rd Law | Every action has an equal, opposite reaction. |
| Kinematic Equation | (s = ut + \tfrac12 at^2) – Displacement with constant acceleration. |
| Work | (W = Fd \cos\theta) – Work = force × distance × cosine of angle. |
| Power | (P = W/t) – Work done per unit time. |
| Energy Conservation | Kinetic + Potential = constant (ignoring friction). |
| Momentum | (p = mv) – Conserved in isolated systems. |
| Gravity (Near Earth) | (F = mg) – Weight = mass × 9.81 m/s². |
| Electric Power | (P = VI = I^2R = V^2/R) – Useful for circuits. |
Tips for the APO Exam
- Link concepts to everyday life – e.g., how the 2nd law explains why a moving cart slows down when a brake is applied.
- Memorize formulas – keep them handy on your cheat sheet.
- Practice quick calculations – timing matters; use approximations when appropriate.
- Stay updated – physics often appears in current affairs (e.g., energy policies, space missions, new materials).
Good luck!