Motion and Time Class 7 Science Best Notes

Key Learning Outcomes

By the end of this lesson, readers will:

✔️ Motion and its types
✔️ Measurement of time
✔️ Speed and its calculation
✔️ Units of speed and time
✔️ Graphical representation of motion
✔️ Applications of motion and time in daily life

Introduction

Motion and time are fundamental concepts in physics. Everything around us moves, from tiny atoms to planets and galaxies. Understanding how motion is measured using time helps us study speed, velocity, and acceleration. This chapter explains different types of motion, ways to measure time, and how speed is calculated. Understanding these concepts is essential for everyday applications, from vehicles moving on roads to celestial bodies orbiting in space.

Motion and Its Types

What is Motion?

Motion is the change in the position of an object with respect to time. If an object does not change its position, it is said to be at rest.

Types of Motion

1. Uniform Motion – An object covers equal distances in equal intervals of time (e.g., a car moving at a constant speed).
   • An object is in uniform motion if it moves equal distances in equal intervals of time.
   • Example: A car moving on a straight highway at a constant speed.
2. Non-Uniform Motion – An object covers unequal distances in equal intervals of time (e.g., a speeding car, a running athlete).
   • An object is in non-uniform motion if it moves unequal distances in equal intervals of time.
   • Example: A cyclist moving in traffic.
3. Periodic Motion – Motion that repeats itself at regular intervals (e.g., pendulum, heartbeat, revolution of Earth).
   • A motion that repeats itself after a fixed interval of time is called periodic motion.
   • Example: A pendulum clock, Earth’s revolution around the Sun.

Measurement of Time

Time is measured using different tools like clocks, stopwatches, and sundials.

• SI unit of time: Second (s)
• Other units: Minutes, Hours, Days, Years

Traditional Methods

• Sundials – Used in ancient times to measure time using the shadow of the Sun.
• Water Clocks – Used flowing water to measure time intervals.
• Hourglasses – Measured time using sand flow.

Modern Methods

• Pendulum Clocks – Based on periodic motion of a pendulum.
• Quartz Clocks – Uses electronic oscillations for accurate timekeeping.
• Stopwatch – Used for measuring small time intervals in sports and experiments.

Interesting Fact:

• Ancient Egyptians used water clocks to measure time!
• Fact: The first mechanical clocks were invented in the 14th century.

Speed and Its Calculation

What is Speed?

Speed is the distance traveled by an object in a given time. It tells us how fast or slow something moves.

Speed Formula:

Speed=Distance/Time

• SI Unit: Meter per Second (m/s)
• Other Units: Kilometer per Hour (km/h), Miles per Hour (mph)

Example: If a car covers 100 km in 2 hours, its speed is:

Types of Speed

• Average Speed = Total distance traveled / Total time taken.
• Instantaneous Speed = Speed of an object at a particular moment (e.g., speedometer reading).

Graphical Representation of Motion

Graphs help us understand motion visually.

• Distance-Time Graph: This shows how an object moves over time.
  • A straight line ➝ Uniform motion
  • A curved line ➝ Non-uniform motion
  • Horizontal Line → Object at Rest

Example Graph:

(Imagine a distance-time graph with time on the X-axis and distance on the Y-axis. A straight diagonal line indicates constant speed.)

Units of Speed and Time

Fact: The speed of light is 3,00,000 km/s!

Applications of Motion and Time in Daily Life

1. Speedometers in vehicles measure speed.
2. Clocks help measure time.
3. Trains, airplanes, and buses use motion and speed calculations.
4. Sports and athletics use timers to measure performance.
5. Traffic control systems use speed calculations.
6. Astronomical calculations involve motion and time concepts.

Important Summary Points

✅ Motion is the change in position of an object over time.
✅ Speed = Distance ÷ Time.
✅ SI Unit of speed is m/s, and time is seconds.
✅ Graphs help in visualizing motion.
✅ Motion is present in everything, from vehicles to the movement of planets.

Interesting Facts About Integers

💡 The word “integer” comes from Latin, meaning “whole.”
💡 In real life, integers are used in thermometers, elevators, bank transactions, and GPS coordinates.
💡 The smallest integer is negative infinity, and the largest integer is positive infinity.

Activity (Exercise):

A. Multiple Choice Questions (MCQs)

1. The motion of a pendulum is an example of:
   a) Linear motion
   b) Circular motion
   c) Oscillatory motion
   d) Random motion
2. Which of the following is NOT a unit of time?
   a) Second
   b) Minute
   c) Kilogram
   d) Hour
3. The speed of an object is defined as:
   a) Distance × Time
   b) Distance ÷ Time
   c) Time ÷ Distance
   d) Acceleration × Time
4. Which instrument is used to measure time accurately?
   a) Thermometer
   b) Stop Watch
   c) Speedometer
   d) Barometer
5. A car moves with a constant speed of 60 km/h. What type of motion is this?
   a) Uniform motion
   b) Non-uniform motion
   c) Oscillatory motion
   d) Rotational motion

B. Fill in the Blanks

1. The SI unit of speed is ________.
2. A body is said to be in motion when its ________ changes with time.
3. The basic unit of time is ________.
4. Speed = ________ ÷ Time.
5. A device used to measure the speed of a vehicle is called a ________.

C. True and False

1. Speed is measured in meters per second (m/s). (True / False)
2. A straight-line distance-time graph represents uniform motion. (True / False)
3. A pendulum of a clock undergoes rotational motion. (True / False)
4. The SI unit of time is hour. (True / False)
5. A moving object can have zero speed. (True / False)

D. Short Answer Questions

1. Define motion with an example.
2. Differentiate between uniform motion and non-uniform motion.
3. What is speed? Write its formula.
4. Define time and its SI unit.
5. What is a speedometer?

E. Long Answer Questions

1. Explain distance-time graphs for:
   • Uniform motion
   • Non-uniform motion
   • Object at rest
2. Define oscillatory motion with two examples.
3. A car covers 180 km in 3 hours. Calculate its speed in m/s.
4. Why is measuring time important in daily life? Give examples.
5. Describe an experiment to measure the speed of a moving object.

F. Numerical Problems

1. A train travels 240 km in 4 hours. Find its speed in m/s.
2. If a car moves at 72 km/h, how much distance will it cover in 30 minutes?
3. A cycle covers 100 meters in 20 seconds. Find its speed.
4. Convert 36 km/h into m/s.
5. A person walks 2 meters per second. How much time will he take to cover 400 meters?

G. Higher Order Thinking Skills (HOTS) Questions

1. If two objects are moving with the same speed, can they have different velocities? Explain.
2. How can you measure the speed of a toy car using a stopwatch?
3. Why do we use light years instead of kilometers to measure distances in space?
4. How do clocks in space differ from clocks on Earth?
5. If the speed of an object is zero, can it still be in motion? Justify your answer.

Quiz:

Coming Soon…

Supplementary Materials:

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• – PDF Guide: “Coming Soon”
• – Cheat Sheet: “Coming Soon”
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