CAIE IGCSE Physics 0625 Theory - Motion, Forces, and Energy

Physical Quantities and Measurement Techniques

Units and Basic Quantities

• Standard: A unit must be chosen before a measurement.
• Basic Quantities: Length, mass, and time.
• SI System: Set of units used globally.

Length

• Unit: Metre (m).
• Multiples: Kilometre (km), gigametre (Gm).
• Measurement: Rulers, meter rules, tape measures for smaller lengths.

Area

• Unit: Square metre (m²).
• Formula: Area = length × breadth.

Volume

• Unit: Cubic metre (m³).
• Measurement: Measuring cylinder for liquids.
• Formula for Cylinder: V = πr²h.

Time

• Unit: Second (s).
• Measurement: Oscillations (e.g., stopwatch).

Scalars and Vectors

• Scalar Quantity: Magnitude only (e.g., distance, speed).
• Vector Quantity: Magnitude and direction (e.g., force, velocity).

Motion

Distance and Displacement

• Distance: Scalar, length travelled.
• Displacement: Vector, includes direction.

Speed and Velocity

• Speed: Distance per unit time.
• Velocity: Speed with direction.

Acceleration

• Definition: Change in velocity per unit time.
• Formula: a = (v-u)/t.

Graphical Representations

• Distance-Time Graph: Shows motion, slope indicates speed.
• Speed-Time Graph: Slope indicates acceleration, area under graph represents distance.

Equations for Constant Acceleration

• First Equation: v = u + at.
• Second Equation: s = ((u+v)/2) × t.

Air Resistance and Free Fall

• Free Fall: Uniform acceleration due to gravity (9.8 m/s²).
• Air Resistance: Affects lighter objects more.
• Terminal Velocity: When air resistance equals weight.

Density

Definition and Calculation

• Density: Mass per unit volume (ρ = m/V).
• Measurement: Regular and irregular shapes, liquids, and air.

Forces

Force Basics

• Definition: Push or pull, changes motion.
• Hooke's Law: Extension proportional to force (F = kx).

Newton's Laws

• First Law: Objects at rest/motion remain so unless acted on.
• Second Law: F = ma, force causes acceleration.

Friction and Air Resistance

• Friction: Opposes motion.
• Types: Static, kinetic, fluid.

Centripetal Force

• Circular Motion: Force towards circle center.
• Factors: Speed, radius, mass.

Moment of a Force

• Definition: Turning effect around a pivot (M = F × d).

Equilibrium

• Principle of Moments: Sum of clockwise = sum of anticlockwise moments.
• Centre of Gravity: Point through which weight acts.

Momentum

Definition and Conservation

• Momentum: Product of mass and velocity (p = mv).
• Conservation: Total momentum constant in isolated systems.

Impulse

• Definition: Change in momentum (J = FΔt).

Energy, Work, and Power

Energy Types

• Kinetic, Potential, Thermal, Nuclear, etc.

Energy Transfers

• Conservation of Energy: Energy cannot be created or destroyed.

Work

• Definition: Force causes displacement (W = F × d).
• Unit: Joule (J).

Power

• Definition: Rate of doing work (P = W/t).
• Unit: Watt (W).

Efficiency

• Formula: (Useful output / Total input) × 100%

Energy Resources

• Types: Fossil fuels, nuclear, renewable (solar, wind, etc.).
• Comparisons: Renewable vs non-renewable.

Pressure

Definition and Calculation

• Pressure: Force per unit area (P = F/A).
• Unit: Pascal (Pa).

Liquid Pressure

• Factors: Depth, density, gravitational field strength.
• Formula: Δp = ρgΔh.