Class 7 Science • Chapter 09

Motion and Time

Vardaan Learning Institute • Detailed Chapter Notes

🏃 1. Types of Motion

⚡ Types of Motion

⬇

Linear / Rectilinear

Motion in a straight line
E.g. falling stone, car on highway, marching soldiers

Circular

Motion in a circular path
E.g. Earth around Sun, a merry-go-round, ceiling fan blade

Periodic / Oscillatory

Motion that repeats at regular intervals
E.g. pendulum, vibrating guitar string, heartbeat, Earth's rotation (day/night)

⏱️ 2. Speed — Measuring How Fast

Speed tells us how much distance is covered in a unit of time. The faster an object moves, the higher its speed.

Speed = Distance ÷ Time | S = D/T | Unit: m/s or km/h

            Unit Conversions:

            • 1 km/h = 1000 m / 3600 s = 5/18 m/s

            • 1 m/s = 3600 m / 1000 km = 18/5 km/h

            Example: A car travels 120 km in 2 hours.

            Speed = 120 km ÷ 2 h = 60 km/h

📐 Triangle Method for Formulas Draw a triangle with D on top and S × T on bottom. Cover the quantity you want to find:
• Cover D → D = S × T
• Cover S → S = D ÷ T
• Cover T → T = D ÷ S

📊 3. Graphs of Motion

            Distance-Time Graph:

            A distance-time (D-T) graph shows how distance changes over time.
            Straight line going upward (slope up) → object is moving at uniform
                        (constant) speed
Horizontal straight line (flat) → object is stationary (not
                        moving)
Curved line (slope increasing) → object is accelerating (speed
                    increasing)
The steeper the slope, the faster the object is moving

        

📸 AI Image Prompt

A three-panel educational graph illustration showing distance-time graphs: Panel 1 "Uniform Speed" — a clean graph with Time (seconds) on x-axis and Distance (metres) on y-axis. A single straight diagonal line going upward from origin (0,0) labeled "Uniform Speed — straight line going upward". The slope is labeled with "Higher slope = Faster speed" and there's a second line with same gradient for comparison. Panel 2 "Object at Rest" — same axes but a flat horizontal line labeled "Stationary/At Rest — no change in distance with time". Panel 3 "Increasing Speed (Acceleration)" — a curved line starting shallow and getting steeper, labeled "Non-uniform speed — line curves upward". All three panels share the same clean art style with labeled axes (Time on x in seconds/minutes, Distance on y in metres/km). Use blue lines on white graph background with gridlines. Bold title above each panel. Teach style educational illustration.

Fig. 9.1 — Types of distance-time graphs

⏰ 4. Measurement of Time — Devices

Era / Device	How it works	Special Note
Ancient methods	Sundials (shadow of gnomon), Water clocks (clepsydra), Sand hourglasses	Not accurate; depended on weather/sunlight
Pendulum Clock	Pendulum swings back and forth at a fixed time period (time of one complete oscillation = time period)	Galileo discovered that period of pendulum depends only on its LENGTH (not its mass or amplitude)
Quartz Clock / Watch	Electric current makes quartz crystal oscillate at very precise frequency	Very accurate; used in digital watches, wall clocks
Atomic Clock	Uses vibrations of atoms (caesium atom); most accurate ever made	Used by GPS satellites, internet servers; error less than 1 second in millions of years!

            The Pendulum:

            A simple pendulum consists of a small heavy ball (called the
            bob) hung from a fixed point by a string. When pulled to one side and released, it swings
            back and forth.

            • One complete back-and-forth swing = ONE oscillation

            • Time for one oscillation = Time Period (T)

            • T depends ONLY on length of the pendulum, NOT on mass of bob or angle of swing

            • Longer pendulum → longer time period (swings more slowly!)

            • Example: A clock pendulum of 1 metre swings back and forth once in about 2 seconds

📝 5. Quick Revision

            Types of motion: Linear (straight line), Circular (around a centre), Periodic
                    (repeats regularly)
Speed = Distance ÷ Time. Unit: m/s (SI) or km/h
1 km/h = 5/18 m/s. 1 m/s = 18/5 km/h
D-T graph: straight line up = uniform speed; flat = stationary; curve = acceleration
Steeper slope in D-T graph = faster speed
Simple pendulum: bob + string. One complete swing = 1 oscillation. Time = Time
                    Period
Time period depends ONLY on length of pendulum, NOT mass or amplitude
Pendulum clock → quartz clock → atomic clock (increasing accuracy)

        