Force, Motion and Energy

Overview

Force, Motion and Energy form the backbone of classical mechanics and appear consistently in OTET Paper II Science. This topic tests your understanding of how objects move, what causes them to move, and how energy transforms during motion. Questions typically involve Newton's laws, calculations of work and kinetic energy, and conceptual problems about friction and momentum.

For OTET, you must master both the conceptual framework (why a ball slows down, why we fall forward when a bus stops) and the quantitative aspects (calculating force, work, power). Examiners often frame questions around everyday situations—pushing a cart, lifting a box, a swinging pendulum—so linking physics to real life is essential. The pedagogy angle also matters: expect questions on how to teach these abstract concepts to upper-primary students using activities and demonstrations.

Key Concepts

• **Force** is a push or pull that can change an object's state of rest or motion, its speed, direction, or shape. Force is a vector quantity with both magnitude and direction.

• **Inertia** is the tendency of an object to resist any change in its state of rest or uniform motion. Mass is a measure of inertia—greater mass means greater inertia.

• **Newton's First Law (Law of Inertia)**: An object remains at rest or in uniform motion unless acted upon by an external unbalanced force.

• **Newton's Second Law**: Force equals mass multiplied by acceleration (F = ma). This law quantifies how force causes acceleration.

• **Newton's Third Law**: For every action, there is an equal and opposite reaction. The two forces act on different bodies.

• **Work** is done when a force moves an object in its direction. Work = Force × Displacement × cos θ. No displacement means no work done.

• **Energy** is the capacity to do work. Kinetic energy is energy of motion; potential energy is stored energy due to position or configuration.

• **Law of Conservation of Energy**: Energy can neither be created nor destroyed, only transformed from one form to another. Total energy in an isolated system remains constant.

Formulas / Key Facts

| Quantity | Formula | Unit | |----------|---------|------| | Force | F = m × a | Newton (N) | | Weight | W = m × g (g ≈ 10 m/s²) | Newton (N) | | Work | W = F × s × cos θ | Joule (J) | | Kinetic Energy | KE = ½ × m × v² | Joule (J) | | Potential Energy | PE = m × g × h | Joule (J) | | Power | P = Work / Time = W/t | Watt (W) | | Momentum | p = m × v | kg·m/s | | Impulse | J = F × t = Δp | N·s or kg·m/s |