Chapter 8: Measurement of Time and Motion
7th StandardScience
Chapter Summary
Measurement of Time and Motion - Chapter Summary
# Measurement of Time and Motion
## Overview
This chapter explores how time has been measured from ancient to modern times using natural events, historical devices, and scientific instruments. It introduces the concept of periodic motion, particularly the pendulum, and explains speed and different types of motion (uniform and non-uniform). The chapter connects scientific concepts with daily life, including sports, transportation, and technological devices.
## Key Topics Covered
### 1. Measurement of Time
* Humans observed natural cycles like sunrise, moon phases, and seasons to track time.
* Ancient time-measuring devices:
* **Sundial** – uses the Sun’s shadow.
* **Water clock** – uses the flow or collection of water.
* **Hourglass** – uses sand to measure time.
* **Candle clock** – uses marked candles that burn over time.
* **Ghatika-yantra** was a sinking bowl-type water clock used in ancient India.
* **Pendulum Clock**: Invented by Christiaan Huygens, inspired by Galileo’s observations.
* **Simple Pendulum**:
* A bob hanging from a thread that swings back and forth.
* **One oscillation**: From mean position to both extreme positions and back.
* **Time period**: Time taken for one oscillation.
* Time period depends on the **length** of the pendulum, not its mass.
### 2. SI Unit of Time
* **Second (s)** is the SI unit.
* 60 seconds = 1 minute (min); 60 minutes = 1 hour (h).
* Symbols should be written in lowercase and without a full stop after them.
### 3. Modern Timekeeping
* **Quartz clocks** and **atomic clocks** are based on tiny, rapid vibrations.
* Atomic clocks are extremely accurate—can lose only 1 second in millions of years.
* Measuring small time intervals (like milliseconds and microseconds) is essential in sports, medicine, music, and technology.
### 4. Speed
* **Speed** = Distance ÷ Time
* SI unit: **m/s** (metres per second); other units: **km/h**
* **Example**: A 3.6 km distance covered in 15 minutes equals a speed of 4 m/s.
#### Speed Calculation Examples
* **Example 1**: Distance = 3.6 km, Time = 15 min → Speed = 4 m/s
* **Example 2**: Distance = 100 km, Time = 2 h → Speed = 50 km/h
* **Example 3**: Distance = 360 km, Speed = 90 km/h → Time = 4 h
### 5. Relationship between Speed, Distance, and Time
* Speed = Distance / Time
* Distance = Speed × Time
* Time = Distance / Speed
### 6. Uniform and Non-uniform Linear Motion
* **Uniform motion**: Object moves equal distances in equal intervals (constant speed).
* **Non-uniform motion**: Object moves unequal distances in equal intervals (changing speed).
* Example from table:
* Train X (uniform): Covers 20 km every 10 minutes.
* Train Y (non-uniform): Covers varying distances in 10 minutes intervals.
## New Terms and Their Simple Meanings
| Term | Simple Definition |
| ------------------ | -------------------------------------------------------------------- |
| Time period | The time it takes for one complete swing (oscillation) of a pendulum |
| Oscillation | One complete to-and-fro movement of a pendulum bob |
| Sundial | A device that tells the time using the shadow cast by the Sun |
| Water clock | A clock that measures time by the flow of water |
| Hourglass | A timer using sand that flows from one bulb to another |
| Candle clock | A candle marked with time intervals that shows time as it burns |
| Pendulum | A swinging object hung from a fixed point, used to measure time |
| SI unit | Internationally accepted standard unit for measuring something |
| Speed | How fast something moves, calculated as distance divided by time |
| Uniform motion | Motion at a constant speed |
| Non-uniform motion | Motion where speed changes over time |
| Quartz clock | A modern clock that uses a crystal to keep time |
| Atomic clock | A very accurate clock that uses atom vibrations to measure time |
| Speedometer | A device in vehicles that shows speed in km/h |
| Odometer | A device in vehicles that measures total distance traveled |
---
## Practice Questions
### Easy (3)
1. **What is the SI unit of time?**
**Answer:** Second (s)
**Explanation:** It is the standard unit used to measure time.
2. **Name one ancient method of measuring time.**
**Answer:** Sundial
**Explanation:** Sundials used the Sun’s shadow to tell the time.
3. **What is a pendulum?**
**Answer:** A bob hanging by a string that swings back and forth.
**Explanation:** It is used to study oscillatory motion and measure time.
---
### Medium (2)
4. **Calculate the speed of a runner who covers 400 m in 50 seconds.**
**Answer:** 8 m/s
**Explanation:** Speed = Distance / Time = 400 / 50 = 8 m/s
5. **Which part of a pendulum decides its time period?**
**Answer:** Length of the string
**Explanation:** The time period depends only on the length, not on the mass of the bob.
---
### Difficult (3)
6. **A car covers 150 metres in 10 seconds. What is its speed in km/h?**
**Answer:** 54 km/h
**Explanation:**
* Speed = 150 m / 10 s = 15 m/s
* Convert to km/h: 15 × (18/5) = 54 km/h
7. **A train travels 180 km in 3 hours. What is its speed in m/s?**
**Answer:** 16.67 m/s
**Explanation:**
* Speed = 180 / 3 = 60 km/h
* Convert to m/s: 60 × (1000/3600) = 16.67 m/s
8. **What is the average speed of a car that travels 60 km in the 1st hour, 70 km in the 2nd, and 50 km in the 3rd?**
**Answer:** 60 km/h
**Explanation:**
* Total distance = 60 + 70 + 50 = 180 km
* Total time = 3 hours
* Average speed = 180 / 3 = 60 km/h
---
### Very Difficult (2)
9. **An object travels 2 km: 500 m at 10 m/s, 500 m at 5 m/s. What speed should it move for the remaining 1 km to complete the journey in 200 s?**
**Answer:** 10 m/s
**Explanation:**
* Time for first 500 m = 500 / 10 = 50 s
* Time for second 500 m = 500 / 5 = 100 s
* Time left = 200 - 50 - 100 = 50 s
* Speed = Distance / Time = 1000 / 50 = 20 m/s
10. **From the table: Time (s): 0, 10, 20, 30, 50, 70 | Distance (m): 0, 8, 24, 32, 40, 56. Fill missing data for uniform motion.**
**Answer:**
* Time = 40 s → Distance = 40 m
* Time = 60 s → Distance = 48 m
**Explanation:** In uniform motion, equal distances in equal time intervals → 8 m every 10 seconds.
---
## Overview
This chapter explores how time has been measured from ancient to modern times using natural events, historical devices, and scientific instruments. It introduces the concept of periodic motion, particularly the pendulum, and explains speed and different types of motion (uniform and non-uniform). The chapter connects scientific concepts with daily life, including sports, transportation, and technological devices.
## Key Topics Covered
### 1. Measurement of Time
* Humans observed natural cycles like sunrise, moon phases, and seasons to track time.
* Ancient time-measuring devices:
* **Sundial** – uses the Sun’s shadow.
* **Water clock** – uses the flow or collection of water.
* **Hourglass** – uses sand to measure time.
* **Candle clock** – uses marked candles that burn over time.
* **Ghatika-yantra** was a sinking bowl-type water clock used in ancient India.
* **Pendulum Clock**: Invented by Christiaan Huygens, inspired by Galileo’s observations.
* **Simple Pendulum**:
* A bob hanging from a thread that swings back and forth.
* **One oscillation**: From mean position to both extreme positions and back.
* **Time period**: Time taken for one oscillation.
* Time period depends on the **length** of the pendulum, not its mass.
### 2. SI Unit of Time
* **Second (s)** is the SI unit.
* 60 seconds = 1 minute (min); 60 minutes = 1 hour (h).
* Symbols should be written in lowercase and without a full stop after them.
### 3. Modern Timekeeping
* **Quartz clocks** and **atomic clocks** are based on tiny, rapid vibrations.
* Atomic clocks are extremely accurate—can lose only 1 second in millions of years.
* Measuring small time intervals (like milliseconds and microseconds) is essential in sports, medicine, music, and technology.
### 4. Speed
* **Speed** = Distance ÷ Time
* SI unit: **m/s** (metres per second); other units: **km/h**
* **Example**: A 3.6 km distance covered in 15 minutes equals a speed of 4 m/s.
#### Speed Calculation Examples
* **Example 1**: Distance = 3.6 km, Time = 15 min → Speed = 4 m/s
* **Example 2**: Distance = 100 km, Time = 2 h → Speed = 50 km/h
* **Example 3**: Distance = 360 km, Speed = 90 km/h → Time = 4 h
### 5. Relationship between Speed, Distance, and Time
* Speed = Distance / Time
* Distance = Speed × Time
* Time = Distance / Speed
### 6. Uniform and Non-uniform Linear Motion
* **Uniform motion**: Object moves equal distances in equal intervals (constant speed).
* **Non-uniform motion**: Object moves unequal distances in equal intervals (changing speed).
* Example from table:
* Train X (uniform): Covers 20 km every 10 minutes.
* Train Y (non-uniform): Covers varying distances in 10 minutes intervals.
## New Terms and Their Simple Meanings
| Term | Simple Definition |
| ------------------ | -------------------------------------------------------------------- |
| Time period | The time it takes for one complete swing (oscillation) of a pendulum |
| Oscillation | One complete to-and-fro movement of a pendulum bob |
| Sundial | A device that tells the time using the shadow cast by the Sun |
| Water clock | A clock that measures time by the flow of water |
| Hourglass | A timer using sand that flows from one bulb to another |
| Candle clock | A candle marked with time intervals that shows time as it burns |
| Pendulum | A swinging object hung from a fixed point, used to measure time |
| SI unit | Internationally accepted standard unit for measuring something |
| Speed | How fast something moves, calculated as distance divided by time |
| Uniform motion | Motion at a constant speed |
| Non-uniform motion | Motion where speed changes over time |
| Quartz clock | A modern clock that uses a crystal to keep time |
| Atomic clock | A very accurate clock that uses atom vibrations to measure time |
| Speedometer | A device in vehicles that shows speed in km/h |
| Odometer | A device in vehicles that measures total distance traveled |
---
## Practice Questions
### Easy (3)
1. **What is the SI unit of time?**
**Answer:** Second (s)
**Explanation:** It is the standard unit used to measure time.
2. **Name one ancient method of measuring time.**
**Answer:** Sundial
**Explanation:** Sundials used the Sun’s shadow to tell the time.
3. **What is a pendulum?**
**Answer:** A bob hanging by a string that swings back and forth.
**Explanation:** It is used to study oscillatory motion and measure time.
---
### Medium (2)
4. **Calculate the speed of a runner who covers 400 m in 50 seconds.**
**Answer:** 8 m/s
**Explanation:** Speed = Distance / Time = 400 / 50 = 8 m/s
5. **Which part of a pendulum decides its time period?**
**Answer:** Length of the string
**Explanation:** The time period depends only on the length, not on the mass of the bob.
---
### Difficult (3)
6. **A car covers 150 metres in 10 seconds. What is its speed in km/h?**
**Answer:** 54 km/h
**Explanation:**
* Speed = 150 m / 10 s = 15 m/s
* Convert to km/h: 15 × (18/5) = 54 km/h
7. **A train travels 180 km in 3 hours. What is its speed in m/s?**
**Answer:** 16.67 m/s
**Explanation:**
* Speed = 180 / 3 = 60 km/h
* Convert to m/s: 60 × (1000/3600) = 16.67 m/s
8. **What is the average speed of a car that travels 60 km in the 1st hour, 70 km in the 2nd, and 50 km in the 3rd?**
**Answer:** 60 km/h
**Explanation:**
* Total distance = 60 + 70 + 50 = 180 km
* Total time = 3 hours
* Average speed = 180 / 3 = 60 km/h
---
### Very Difficult (2)
9. **An object travels 2 km: 500 m at 10 m/s, 500 m at 5 m/s. What speed should it move for the remaining 1 km to complete the journey in 200 s?**
**Answer:** 10 m/s
**Explanation:**
* Time for first 500 m = 500 / 10 = 50 s
* Time for second 500 m = 500 / 5 = 100 s
* Time left = 200 - 50 - 100 = 50 s
* Speed = Distance / Time = 1000 / 50 = 20 m/s
10. **From the table: Time (s): 0, 10, 20, 30, 50, 70 | Distance (m): 0, 8, 24, 32, 40, 56. Fill missing data for uniform motion.**
**Answer:**
* Time = 40 s → Distance = 40 m
* Time = 60 s → Distance = 48 m
**Explanation:** In uniform motion, equal distances in equal time intervals → 8 m every 10 seconds.
---
Measurement of Time and Motion
Overview
This chapter explores how time has been measured from ancient to modern times using natural events, historical devices, and scientific instruments. It introduces the concept of periodic motion, particularly the pendulum, and explains speed and different types of motion (uniform and non-uniform). The chapter connects scientific concepts with daily life, including sports, transportation, and technological devices.
Key Topics Covered
1. Measurement of Time
-
Humans observed natural cycles like sunrise, moon phases, and seasons to track time.
-
Ancient time-measuring devices:
- Sundial – uses the Sun’s shadow.
- Water clock – uses the flow or collection of water.
- Hourglass – uses sand to measure time.
- Candle clock – uses marked candles that burn over time.
-
Ghatika-yantra was a sinking bowl-type water clock used in ancient India.
-
Pendulum Clock: Invented by Christiaan Huygens, inspired by Galileo’s observations.
-
Simple Pendulum:
- A bob hanging from a thread that swings back and forth.
- One oscillation: From mean position to both extreme positions and back.
- Time period: Time taken for one oscillation.
- Time period depends on the length of the pendulum, not its mass.
2. SI Unit of Time
- Second (s) is the SI unit.
- 60 seconds = 1 minute (min); 60 minutes = 1 hour (h).
- Symbols should be written in lowercase and without a full stop after them.
3. Modern Timekeeping
- Quartz clocks and atomic clocks are based on tiny, rapid vibrations.
- Atomic clocks are extremely accurate—can lose only 1 second in millions of years.
- Measuring small time intervals (like milliseconds and microseconds) is essential in sports, medicine, music, and technology.
4. Speed
- Speed = Distance ÷ Time
- SI unit: m/s (metres per second); other units: km/h
- Example: A 3.6 km distance covered in 15 minutes equals a speed of 4 m/s.
Speed Calculation Examples
- Example 1: Distance = 3.6 km, Time = 15 min → Speed = 4 m/s
- Example 2: Distance = 100 km, Time = 2 h → Speed = 50 km/h
- Example 3: Distance = 360 km, Speed = 90 km/h → Time = 4 h
5. Relationship between Speed, Distance, and Time
- Speed = Distance / Time
- Distance = Speed × Time
- Time = Distance / Speed
6. Uniform and Non-uniform Linear Motion
-
Uniform motion: Object moves equal distances in equal intervals (constant speed).
-
Non-uniform motion: Object moves unequal distances in equal intervals (changing speed).
-
Example from table:
- Train X (uniform): Covers 20 km every 10 minutes.
- Train Y (non-uniform): Covers varying distances in 10 minutes intervals.
New Terms and Their Simple Meanings
| Term | Simple Definition |
|---|---|
| Time period | The time it takes for one complete swing (oscillation) of a pendulum |
| Oscillation | One complete to-and-fro movement of a pendulum bob |
| Sundial | A device that tells the time using the shadow cast by the Sun |
| Water clock | A clock that measures time by the flow of water |
| Hourglass | A timer using sand that flows from one bulb to another |
| Candle clock | A candle marked with time intervals that shows time as it burns |
| Pendulum | A swinging object hung from a fixed point, used to measure time |
| SI unit | Internationally accepted standard unit for measuring something |
| Speed | How fast something moves, calculated as distance divided by time |
| Uniform motion | Motion at a constant speed |
| Non-uniform motion | Motion where speed changes over time |
| Quartz clock | A modern clock that uses a crystal to keep time |
| Atomic clock | A very accurate clock that uses atom vibrations to measure time |
| Speedometer | A device in vehicles that shows speed in km/h |
| Odometer | A device in vehicles that measures total distance traveled |
Practice Questions
Easy (3)
-
What is the SI unit of time? Answer: Second (s) Explanation: It is the standard unit used to measure time.
-
Name one ancient method of measuring time. Answer: Sundial Explanation: Sundials used the Sun’s shadow to tell the time.
-
What is a pendulum? Answer: A bob hanging by a string that swings back and forth. Explanation: It is used to study oscillatory motion and measure time.
Medium (2)
-
Calculate the speed of a runner who covers 400 m in 50 seconds. Answer: 8 m/s Explanation: Speed = Distance / Time = 400 / 50 = 8 m/s
-
Which part of a pendulum decides its time period? Answer: Length of the string Explanation: The time period depends only on the length, not on the mass of the bob.
Difficult (3)
-
A car covers 150 metres in 10 seconds. What is its speed in km/h? Answer: 54 km/h Explanation:
- Speed = 150 m / 10 s = 15 m/s
- Convert to km/h: 15 × (18/5) = 54 km/h
-
A train travels 180 km in 3 hours. What is its speed in m/s? Answer: 16.67 m/s Explanation:
- Speed = 180 / 3 = 60 km/h
- Convert to m/s: 60 × (1000/3600) = 16.67 m/s
-
What is the average speed of a car that travels 60 km in the 1st hour, 70 km in the 2nd, and 50 km in the 3rd? Answer: 60 km/h Explanation:
- Total distance = 60 + 70 + 50 = 180 km
- Total time = 3 hours
- Average speed = 180 / 3 = 60 km/h
Very Difficult (2)
-
An object travels 2 km: 500 m at 10 m/s, 500 m at 5 m/s. What speed should it move for the remaining 1 km to complete the journey in 200 s? Answer: 10 m/s Explanation:
- Time for first 500 m = 500 / 10 = 50 s
- Time for second 500 m = 500 / 5 = 100 s
- Time left = 200 - 50 - 100 = 50 s
- Speed = Distance / Time = 1000 / 50 = 20 m/s
-
From the table: Time (s): 0, 10, 20, 30, 50, 70 | Distance (m): 0, 8, 24, 32, 40, 56. Fill missing data for uniform motion. Answer:
- Time = 40 s → Distance = 40 m
- Time = 60 s → Distance = 48 m Explanation: In uniform motion, equal distances in equal time intervals → 8 m every 10 seconds.