MG SCHOOL SCIENCE

CLASS 7 SCIENCE

MEASUREMENT OF TIME AND MOTION

Complete Chapter Notes | Definitions | Formulas | Solved Examples

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📘 CLASS 7

🔬 SCIENCE

⭐ CHAPTER NOTES

📑 CHAPTER CONTENTS

Introduction Measurement of Time Simple Pendulum SI Units Speed Formulas Types of Motion Definitions Questions MCQ Test

1. Introduction

Time and motion are important concepts in our everyday life. We use clocks to measure time and different instruments to measure the speed and distance travelled by objects.

From a running athlete to a moving train, everything around us can be studied through the concepts of time, distance and motion.

Learning Objectives

Understand different methods of measuring time.
Learn the working of a simple pendulum.
Understand speed and its mathematical formula.
Differentiate uniform and non-uniform motion.
Solve numerical problems based on speed.

2. Measurement of Time

Since ancient times, people have observed natural events to understand the passage of time.

Ancient Methods of Measuring Time

1. Sundial

A sundial uses the shadow of an object produced by sunlight to indicate the time of day.

2. Water Clock

A water clock measures time through the controlled flow of water from one container to another.

3. Hourglass

An hourglass measures time using sand flowing through a narrow opening from the upper chamber to the lower chamber.

4. Candle Clock

A candle clock measures the passage of time by observing how much of a marked candle burns.

Interesting Fact: The Samrat Yantra at Jantar Mantar, Jaipur, is a giant sundial used for astronomical observations and time measurement.

Development of Clocks

Ancient people used natural cycles and simple devices.
Mechanical clocks developed using gears and weights.
Pendulum clocks improved timekeeping accuracy.
Modern clocks use quartz crystals and atomic transitions.

3. The Simple Pendulum

Simple Pendulum: A simple pendulum consists of a small heavy object called a bob suspended from a fixed support by a light string.

Diagram of a Simple Pendulum

A – Left extreme | O – Mean position | B – Right extreme

Important Terms

Bob: The small heavy object suspended by a string.
Mean position: The central resting position of the bob.
Extreme positions: The farthest positions on either side.
Oscillation: One complete to-and-fro movement.
Time period: Time taken to complete one oscillation.

One Complete Oscillation: Movement from one extreme position to the other extreme position and back to the starting extreme position.

Experiment: Finding the Time Period

Take a string and tie a small heavy bob to one end.
Fix the other end to a rigid support.
Displace the bob slightly and release it.
Measure the time taken for 10 oscillations.
Divide the total time by 10.

Time Period = Total Time / Number of Oscillations

The time period of a simple pendulum depends on its length. For small oscillations, it does not depend on the mass of the bob.

4. SI Units of Time

The SI unit of time is the second.

Unit	Symbol	Conversion
Second	s	Standard unit
Minute	min	1 min = 60 s
Hour	h	1 h = 60 min
Day	d	1 day = 24 h

1 hour = 60 × 60 = 3600 seconds

5. Slow or Fast and Speed

When two objects cover different distances in the same time, the object covering more distance is moving faster.

Speed: Speed is the distance travelled by an object per unit time.

Speed = Total Distance / Total Time

Units of Speed

Metre per second (m/s)
Kilometre per hour (km/h)

Measuring Instruments

Speedometer: Measures the speed of a vehicle.
Odometer: Measures the total distance travelled by a vehicle.

Vehicle Measuring Instruments

Speedometer → Speed

Odometer → Distance travelled

6. Relationship Between Speed, Distance and Time

Speed = Distance / Time

Distance = Speed × Time

Time = Distance / Speed

Speed Formula Triangle

Cover the quantity you want to calculate to find its formula.

Solved Example 1

Question: A cyclist travels 5 km in 1 hour. Find the speed.

Given:

Distance = 5 km
Time = 1 hour

Formula:

Speed = Distance / Time

Calculation:

Speed = 5 / 1 = 5 km/h

Answer: 5 km/h.

Solved Example 2

Question: A car moves at 60 km/h for 3 hours. Find the distance.

Distance = Speed × Time

= 60 × 3

= 180 km

Answer: 180 km.

Solved Example 3

Question: A train travels 240 km at 80 km/h. Calculate the time.

Time = Distance / Speed

= 240 / 80

= 3 hours

Answer: 3 hours.

Unit Conversion

To convert km/h into m/s, multiply by 5/18.

To convert m/s into km/h, multiply by 18/5.

Example: Convert 72 km/h into m/s. 72 × 5/18 = 20 m/s. Answer: 20 m/s.

7. Uniform and Non-uniform Linear Motion

Linear Motion

Motion of an object along a straight line is called linear motion.

Uniform Linear Motion

An object is said to be in uniform linear motion when it travels equal distances in equal intervals of time along a straight line.

Uniform Motion

Time Interval	Distance
1st minute	10 m
2nd minute	10 m
3rd minute	10 m

Non-uniform Linear Motion

An object is said to be in non-uniform linear motion when it travels unequal distances in equal intervals of time along a straight line.

Non-uniform Motion

Time Interval	Distance
1st minute	10 m
2nd minute	15 m
3rd minute	8 m

Uniform Motion	Non-uniform Motion
Equal distances in equal time intervals.	Unequal distances in equal time intervals.
Constant speed.	Changing speed.
Example: Ideal constant-speed motion on a straight track.	Example: A vehicle changing speed on a road.

8. Important Definitions

1. Sundial: An instrument that uses the Sun's shadow to indicate time.

2. Water Clock: A device that measures time through the flow of water.

3. Hourglass: A device that measures time using flowing sand.

4. Pendulum: A suspended object that swings to and fro.

5. Oscillation: One complete to-and-fro movement.

6. Time Period: Time taken to complete one oscillation.

7. Speed: Distance travelled per unit time.

8. Average Speed: Total distance travelled divided by total time taken.

9. Linear Motion: Motion along a straight line.

10. Uniform Motion: Equal distances travelled in equal time intervals.

11. Non-uniform Motion: Unequal distances travelled in equal time intervals.

12. Speedometer: Instrument used to measure the speed of a vehicle.

13. Odometer: Instrument used to measure the distance travelled by a vehicle.

9. Important Questions and Answers

Q1. What is the SI unit of time?

The SI unit of time is the second (s).

Q2. What is a simple pendulum?

A simple pendulum consists of a small heavy bob suspended from a fixed support by a light string.

Q3. Define time period.

The time taken by a pendulum to complete one oscillation is called its time period.

Q4. What is speed?

Speed is the distance travelled by an object per unit time.

Q5. Write the formula for speed.

Speed = Total distance travelled / Total time taken.

Q6. What is the difference between a speedometer and an odometer?

A speedometer measures the speed of a vehicle, whereas an odometer measures the total distance travelled.

Q7. What is uniform linear motion?

Motion along a straight line in which equal distances are covered in equal intervals of time is called uniform linear motion.

Q8. What is non-uniform linear motion?

Motion along a straight line in which unequal distances are covered in equal intervals of time is called non-uniform linear motion.

Q9. What is average speed?

Average speed is the ratio of total distance travelled to the total time taken.

Q10. Name four ancient devices used to measure time.

Sundial, water clock, hourglass and candle clock.

11. Quick Revision

Remember These Important Points

Second is the SI unit of time.
Speed = Distance / Time.
Distance = Speed × Time.
Time = Distance / Speed.
Speedometer measures speed.
Odometer measures distance.
Uniform motion covers equal distances in equal time intervals.
Non-uniform motion covers unequal distances in equal time intervals.
One complete to-and-fro movement is one oscillation.

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Wednesday, 11 November 2026

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