Lesson Overview

Unit 2 covers the fundamental principles of motion and forces. Students learn about linear and projectile motion, Newton’s laws, equilibrium, moments, rotational motion, energy, power, and fluids. These concepts form the backbone of classical mechanics.

1. Core Concepts (Short Notes)

2.1 Linear & Projectile Motion

• Motion in one dimension: displacement, velocity, acceleration.

• Equations of motion (SUVAT).

• Relative velocity.

• Projectile motion: horizontal and vertical components.

2.2 Forces & Resultants

• Parallelogram law of forces.

• Component method of resolution.

• Centre of gravity and moment of forces.

2.3 Newton’s Laws of Motion

• 1st law: Inertia.

• 2nd law: F = ma.

• 3rd law: Action–reaction.

• Momentum & impulse.

• Friction (static & dynamic).

2.4 Equilibrium of Forces

• Conditions for equilibrium:

  • ΣF = 0

  • ΣM = 0

• Triangle of forces.

• Principle of moments.

2.5 Rotational Motion

• Angular displacement, velocity, acceleration.

• Equations of rotational motion.

• Torque.

• Moment of inertia: I = Σmr².

2.6 Energy, Work & Power

• Work done: W = Fd cosθ.

• Kinetic & potential energy.

• Conservation of energy.

• Efficiency.

2.7 Fluids at Rest

• Pressure.

• Pascal’s principle.

• Archimedes’ principle.

• Density & relative density.

2.8 Fluids in Motion

• Continuity equation.

• Bernoulli’s principle.

• Applications: atomizer, carburettor, aircraft lift.

Detailed Notes for Each Section

2.1 Linear Motion & Projectile Motion

Key Definitions

• Displacement (s): Distance in a specific direction.

• Velocity (v): Rate of change of displacement.

• Acceleration (a): Rate of change of velocity.

Equations of Motion (SUVAT)

1. v = u + at

2. s = ut + ½at²

3. v² = u² + 2as

Projectile Motion

• Horizontal velocity: constant.

• Vertical velocity: uniformly accelerated.

• Time of flight: T = 2u sinθ / g

• Range: R = u² sin2θ / g

2.2 Forces, Resultants & Moments

Resolving Forces

• Fx = F cosθ

• Fy = F sinθ

Parallelogram Law

Resultant is represented by diagonal.

Moment of a Force

• Moment = F × perpendicular distance.

• Clockwise = positive or negative (convention-based).

Centre of Gravity

• Point where weight appears to act.

2.3 Newton’s Laws

First Law (Inertia)

• Objects remain at rest or uniform motion unless acted on by a net force.

Second Law

• F = ma

• Impulse = Change in momentum (Ft = mv – mu).

Third Law

• Every action has an equal and opposite reaction.

Friction

• Static friction: Opposes starting motion.

• Dynamic friction: Opposes motion.

• μ = Ff / N

2.4 Equilibrium of Forces

Conditions

• ΣFx = 0

• ΣFy = 0

• ΣMoments = 0

Triangle of Forces

Used when three forces act at a point.

Principle of Moments

• Clockwise moments = Anticlockwise moments.

• Used to determine unknown forces.

2.5 Rotational Motion

Angular Quantities

• Angular displacement (θ): radians

• Angular velocity (ω): rad s⁻¹

• Angular acceleration (α): rad s⁻²

Rotational Equations

1. ω = ω₀ + αt

2. θ = ω₀t + ½αt²

3. ω² = ω₀² + 2αθ

Moment of Inertia

• I = Σmr²

• Depends on mass distribution.

2.6 Work, Energy & Power

Work Done

W = Fd cosθ

Energy

• Kinetic: ½mv²

• Potential: mgh

Conservation of Energy

Energy cannot be created or destroyed.

Power

P = W/t = Fv

2.7 Fluids at Rest

Density

Pressure in Fluids

Pascal’s Law

Pressure applied to a fluid is transmitted equally.

Archimedes’ Principle

2.8 Fluids in Motion

Equation of Continuity

Bernoulli’s Principle

Applications

• Atomizer

• Aeroplane lift

• Venturi effect

3. Formula Summary for Unit 2

• v = u + at

• s = ut + ½at²

• F = ma

• p = mv

• Moment = F × d

• W = Fd cosθ

• KE = ½mv²

• PE = mgh

• P = Fv

• P = hρg

• A₁v₁ = A₂v₂

4. Common Mistakes to Avoid

• Forgetting direction when adding vectors.

• Mixing scalar and vector quantities.

• Taking wrong components in projectile motion.

• Incorrect substitution of g = 9.8 or 10 m/s² depending on exam.

• Using wrong distance for torque (must be perpendicular).

5. Exam Tips

• Always draw diagrams for force and motion problems.

• Separate horizontal and vertical components in projectile motion.

• Write Newton’s 3rd Law pairs clearly.

• Use ΣM = 0 to solve equilibrium questions efficiently.

• For Bernoulli applications, remember: fast fluid = low pressure.

6. Quick Revision Table