Chapter 3: Dynamics

Newton's First Law establishes that objects maintain their state of rest or uniform motion unless an external force acts upon them, a property called inertia that depends directly on an object's mass. Newton's Second Law quantifies this relationship through the equation force equals mass times acceleration, demonstrating that acceleration is proportional to applied force and occurs in the force's direction. Newton's Third Law reveals that forces always occur in pairs: when one object exerts a force on another, the second object exerts an equal but opposite force on the first, with both forces acting on different bodies. The chapter clarifies the fundamental distinction between mass, an intrinsic property measured in kilograms that represents inertia and remains constant everywhere, and weight, a gravitational force measured in newtons that varies depending on the local gravitational field. Understanding forces requires identifying all forces acting on an object, including contact forces, tension, friction, and upthrust, and determining whether they balance to produce equilibrium or remain unbalanced to create acceleration. The chapter addresses motion through fluids by explaining drag or air resistance as the resistive force opposing movement, which increases with velocity until it balances weight, producing terminal velocity where acceleration ceases. Additionally, the chapter emphasizes the importance of SI units in physics, covering base units of length in metres, mass in kilograms, and time in seconds, from which derived units like the newton are constructed. All valid physics equations must maintain dimensional homogeneity, meaning units must be consistent on both sides of the equation, and SI prefixes handle extremely large or small quantities systematically.