Physics
Motion — Describing the Moving World
What's inside this booklet?
Scalars & vectors • Distance, displacement, speed, velocity, acceleration • Equations of
motion (derivation) • Distance-time and velocity-time graphs • Uniform circular motion •
Newton's laws & projectile motion (X–XII extensions) • MCQs, Assertion–Reason, numerical
problems, T/F, FIB, match-the-following, one-word.
Tip
Always check the units — SI units are the global standard. Position → m, Time → s,
Velocity → m s-1, Acceleration → m s-2.
1. Motion — An Introduction
An object is said to be in motion if its position changes with time with respect to its
surroundings. Motion is everywhere — a falling apple, a running athlete, the orbit of the Moon, the
vibration of an atom. To study motion scientifically, we need well-defined quantities and a frame of
reference.
Frame of Reference
A coordinate system attached to an observer. Whether an object is in motion or at rest
depends on the chosen frame. A passenger on a moving train is at rest with respect to the
train but in motion with respect to the platform.
1.1 Types of Motion
• Translatory motion: all points of the body move through equal distances (rectilinear: car on a
straight road; curvilinear: a kicked football).
• Rotatory motion: body spins about a fixed axis (a ceiling fan).
, • Vibratory / oscillatory motion: back-and-forth motion (pendulum, vibrating string).
• Periodic motion: motion that repeats itself in equal intervals of time (planetary motion).
• Random motion: direction changes irregularly (Brownian motion of pollen grains).
2. Scalars and Vectors
Property Scalar Vector
Definition Has magnitude only Has both magnitude and direction
Examples Distance, speed, mass, time, energy Displacement, velocity, acceleration, force
Algebra Ordinary algebraic rules Triangle / Parallelogram law of addition
Notation Plain letter (m) Bold or arrow (F or F⃗)
3. Distance and Displacement
Distance is the actual length of the path travelled (scalar). Displacement is the shortest straight-
line distance from the initial to final position with direction (vector). Displacement can be zero,
positive or negative; distance is always positive and ≥ |displacement|.
Worked Example
A boy walks 3 m east, then 4 m north. Distance = 3 + 4 = 7 m.
Displacement = √(3² + 4²) = 5 m, in the direction N 36.87° E.
4. Speed and Velocity
Speed = distance ÷ time, scalar. Velocity = displacement ÷ time, vector. SI unit of both is m s-1.
Type Definition Example
Equal distances in equal time A train at constant 60 km h¹ on a
Uniform motion
intervals straight track
Non-uniform Unequal distances in equal time
A car in city traffic
motion intervals
Motion — Describing the Moving World
What's inside this booklet?
Scalars & vectors • Distance, displacement, speed, velocity, acceleration • Equations of
motion (derivation) • Distance-time and velocity-time graphs • Uniform circular motion •
Newton's laws & projectile motion (X–XII extensions) • MCQs, Assertion–Reason, numerical
problems, T/F, FIB, match-the-following, one-word.
Tip
Always check the units — SI units are the global standard. Position → m, Time → s,
Velocity → m s-1, Acceleration → m s-2.
1. Motion — An Introduction
An object is said to be in motion if its position changes with time with respect to its
surroundings. Motion is everywhere — a falling apple, a running athlete, the orbit of the Moon, the
vibration of an atom. To study motion scientifically, we need well-defined quantities and a frame of
reference.
Frame of Reference
A coordinate system attached to an observer. Whether an object is in motion or at rest
depends on the chosen frame. A passenger on a moving train is at rest with respect to the
train but in motion with respect to the platform.
1.1 Types of Motion
• Translatory motion: all points of the body move through equal distances (rectilinear: car on a
straight road; curvilinear: a kicked football).
• Rotatory motion: body spins about a fixed axis (a ceiling fan).
, • Vibratory / oscillatory motion: back-and-forth motion (pendulum, vibrating string).
• Periodic motion: motion that repeats itself in equal intervals of time (planetary motion).
• Random motion: direction changes irregularly (Brownian motion of pollen grains).
2. Scalars and Vectors
Property Scalar Vector
Definition Has magnitude only Has both magnitude and direction
Examples Distance, speed, mass, time, energy Displacement, velocity, acceleration, force
Algebra Ordinary algebraic rules Triangle / Parallelogram law of addition
Notation Plain letter (m) Bold or arrow (F or F⃗)
3. Distance and Displacement
Distance is the actual length of the path travelled (scalar). Displacement is the shortest straight-
line distance from the initial to final position with direction (vector). Displacement can be zero,
positive or negative; distance is always positive and ≥ |displacement|.
Worked Example
A boy walks 3 m east, then 4 m north. Distance = 3 + 4 = 7 m.
Displacement = √(3² + 4²) = 5 m, in the direction N 36.87° E.
4. Speed and Velocity
Speed = distance ÷ time, scalar. Velocity = displacement ÷ time, vector. SI unit of both is m s-1.
Type Definition Example
Equal distances in equal time A train at constant 60 km h¹ on a
Uniform motion
intervals straight track
Non-uniform Unequal distances in equal time
A car in city traffic
motion intervals
