Physics basics

Physics Basics – AWS Certification Study Notes

Subject: General Awareness & Current Affairs
Topic: Physics Basics

1. Simple Explanation

Physics is the science that studies matter, energy, and the interactions between them. In the context of AWS and cloud computing, a solid grasp of physics fundamentals helps you understand hardware performance, data center design, and emerging technologies such as quantum computing and AI accelerators.

Key areas to master:

2. Key Points (Bullet-Style)

Kinematics & Motion

• Displacement (Δx) – change in position (vector).
• Velocity (v) – Δx divided by time t (scalar or vector).
• Acceleration (a) – change in velocity per unit time.
• Equations of motion (for constant acceleration):
  1. ( v = u + a t )
  2. ( s = u t + \frac{1}{2} a t^2 )
  3. ( v^2 = u^2 + 2 a s )

Newton’s Laws

1. First Law – an object remains in its state of rest or uniform motion unless acted upon.
2. Second Law – ( F = m a ) (force equals mass times acceleration).
3. Third Law – for every action there is an equal and opposite reaction.

Work & Energy

• Work (W) – ( W = F \cdot d \cdot \cos\theta ).
• Kinetic Energy (KE) – ( KE = \frac{1}{2} m v^2 ).
• Potential Energy (PE) – e.g., gravitational ( PE = m g h ).
• Conservation of Energy – total energy in an isolated system remains constant.

Power

• Instantaneous Power (P) – ( P = \frac{dW}{dt} = F \cdot v ).
• Average Power – ( P_{\text{avg}} = \frac{W_{\text{total}}}{t_{\text{total}}} ).
• Electrical Power – ( P = V \times I ).

Thermodynamics

• First Law – ( \Delta U = Q - W ) (change in internal energy = heat added – work done).
• Heat Transfer – conduction, convection, radiation.
• Efficiency – ( \eta = \frac{\text{Useful Work}}{\text{Heat Input}} ).

Electromagnetism

• Coulomb’s Law – force between charges.
• Faraday’s Law – induced EMF = (-\frac{d\Phi_B}{dt}).
• Ohm’s Law – ( V = I R ).
• Kirchhoff’s Laws – for current & voltage in circuits.

Quantum Concepts (Brief)

• Quantum states – discrete energy levels.
• Superposition – system can exist in multiple states simultaneously.
• Entanglement – correlation between particles regardless of distance.

3. Worked Example

Problem

A server rack contains a hard‑disk drive (HDD) weighing 10 kg. During a power‑on sequence, the HDD spins up from rest to 5000 rpm (≈ 523 rad/s) in 5 s.
Assume the HDD’s moment of inertia ( I = 0.02,\text{kg·m}^2 ).
Questions

1. What is the angular acceleration of the HDD?
2. What torque must be applied to achieve this acceleration?
3. How much kinetic energy is stored in the spinning HDD?

Solution

1. Angular acceleration ( \alpha )

[ \alpha = \frac{\Delta \omega}{\Delta t} = \frac{523,\text{rad/s} - 0}{5,\text{s}} = 104.6,\text{rad/s}^2 ]

2. Required torque ( \tau )

Newton’s second law for rotation:
[ \tau = I \alpha = 0.02,\text{kg·m}^2 \times 104.6,\text{rad/s}^2 = 2.092,\text{N·m} ]

3. Rotational kinetic energy ( KE_{\text{rot}} )

[ KE_{\text{rot}} = \frac{1}{2} I \omega^2 = \frac{1}{2} \times 0.02 \times (523)^2 \approx 2735,\text{J} ]

Interpretation

• A torque of about 2 N·m is required to spin up the HDD in 5 s.
• The HDD stores roughly 2.7 kJ of kinetic energy, which is dissipated as heat during spin‑down.
• Understanding these numbers helps design power‑supply units and cooling systems in AWS data centers.

4. Quick Revision Summary