Physics — Motion and Gravitation

Overview

Motion and Gravitation forms a foundational chapter in upper-primary science, appearing consistently in KAR TET Paper II. This topic tests your understanding of how objects move, why they move, and what governs their motion under gravitational influence. Questions typically involve numerical problems using equations of motion, conceptual questions on Newton's laws, and application-based problems on free fall and gravitational force.

Mastering this topic requires a clear grasp of definitions (distance vs displacement, speed vs velocity), the three equations of motion, Newton's three laws, and the universal law of gravitation. Expect 3–5 questions combining direct formula application with conceptual reasoning about everyday phenomena like falling objects, moving vehicles, and planetary motion.

Key Concepts

• **Rest and Motion are relative**: An object is at rest or in motion only with respect to a reference point. A passenger in a moving bus is at rest relative to the bus but in motion relative to the road.

• **Distance vs Displacement**: Distance is the total path length (scalar, always positive); displacement is the shortest straight-line distance from initial to final position (vector, can be zero or negative).

• **Speed vs Velocity**: Speed = distance/time (scalar); velocity = displacement/time (vector). An object moving in a circle at constant speed has changing velocity because direction changes.

• **Uniform vs Non-uniform Motion**: Uniform motion has constant velocity (zero acceleration); non-uniform motion has changing velocity (non-zero acceleration).

• **Acceleration**: Rate of change of velocity. Positive acceleration means speeding up in the direction of motion; negative acceleration (retardation/deceleration) means slowing down.

• **Newton's First Law (Inertia)**: An object remains at rest or in uniform motion unless acted upon by an external unbalanced force. Explains why passengers lurch forward when a bus stops suddenly.

• **Newton's Second Law**: Force = mass × acceleration (F = ma). Greater mass requires greater force for the same acceleration.

• **Newton's Third Law**: Every action has an equal and opposite reaction. The forces act on different bodies — a swimmer pushes water backward, water pushes swimmer forward.

• **Universal Law of Gravitation**: Every object attracts every other object with a force proportional to the product of their masses and inversely proportional to the square of the distance between them.