Force, Motion and Energy

Overview

Force, Motion and Energy forms the backbone of classical mechanics and is a high-scoring topic in Bihar TET Paper II Science. This chapter connects everyday experiences—pushing a cart, a ball rolling downhill, a moving train—to fundamental physics principles that govern how objects behave. Expect 3–5 questions testing conceptual clarity on Newton's laws, work-energy calculations, and the relationship between force and motion.

Mastery here requires understanding three interconnected ideas: (1) forces cause changes in motion, (2) work transfers energy between objects, and (3) energy is conserved but transforms between forms. Students often memorise formulas but struggle with application—Bihar TET typically includes scenario-based questions where you must identify which law applies or calculate work/energy in practical situations.

Key Concepts

• **Force**: A push or pull that can change an object's state of rest or uniform motion. Measured in Newtons (N). Force is a vector—it has both magnitude and direction.

• **Inertia**: The tendency of an object to resist changes in its state of motion. Mass is the measure of inertia—heavier objects have greater inertia.

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

• **Newton's Second Law**: Force equals mass times acceleration (F = ma). This quantifies how force produces acceleration—greater force means greater acceleration; greater mass means less acceleration for the same force.

• **Newton's Third Law**: For every action, there is an equal and opposite reaction. Action and reaction forces act on different bodies, not the same body.

• **Work**: Work is done when a force moves an object in the direction of the force. Work = Force × Displacement × cos θ. If displacement is zero or force is perpendicular to motion, work done is zero.

• **Energy**: The capacity to do work. Kinetic energy (energy of motion) and potential energy (stored energy due to position or configuration) are the two main mechanical forms.

• **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

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