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Chapter 5. Measurement of Length and Motion

Chapter 5. Measurement of Length and Motion

Measurement is an essential part of our daily life. We measure the length of objects, the distance between places, and the movement of different objects around us. Accurate measurement helps us perform scientific experiments, construct buildings, manufacture machines, play sports, and carry out many everyday activities. This chapter explains the importance of standard units of measurement, different measuring instruments, correct methods of measuring length, reference points, and various types of motion.

CBSE Notes - Key Points

The following notes provide important definitions, scientific terms, formulas, and key facts from the chapter. These notes are useful for quick revision before school examinations and CBSE assessments.

Important Keywords

• Measurement
• Length
• SI Unit
• Metre (m)
• Centimetre (cm)
• Millimetre (mm)
• Kilometre (km)
• Reference Point
• Rest
• Motion
• Linear Motion
• Circular Motion
• Oscillatory Motion
• Periodic Motion
• Parallax Error
• Measuring Tape
• Metre Scale
• Ruler
• Standard Unit
• Ancient Units

Important Definitions

Measurement: The process of finding the length, distance, or size of an object by comparing it with a standard unit.

Length: The distance between two ends of an object.

SI Unit: The internationally accepted standard unit used for scientific measurements.

Metre: The SI unit of length represented by the symbol m.

Reference Point: A fixed object or place used to describe the position or motion of another object.

Rest: A body is said to be at rest if its position does not change with time with respect to a reference point.

Motion: A body is said to be in motion if its position changes with time with respect to a reference point.

Linear Motion: Motion of an object along a straight path.

Circular Motion: Motion of an object along a circular path around a fixed point.

Oscillatory Motion: The repeated to-and-fro motion of an object about its mean position.

Periodic Motion: Motion that repeats itself after equal intervals of time.

Parallax Error: The error caused when a scale is read from an angle instead of vertically above the marking.

Important Unit Conversions

Unit	Equivalent Value
1 kilometre	1000 metres
1 metre	100 centimetres
1 centimetre	10 millimetres
1000 millimetres	1 metre

Measuring Instruments

Instrument	Used For
Ruler	Small objects like pencils and notebooks
Metre Scale	Large objects like tables and doors
Measuring Tape	Curved objects, cloth, and body measurements

Important Facts

• The SI unit of length is the metre.
• Standard units are accepted throughout the world.
• Body-part measurements are not reliable because they differ from person to person.
• A ruler should always be placed exactly along the object being measured.
• The eye should be kept vertically above the scale to avoid parallax error.
• A damaged ruler can still be used by taking the difference between two readings.
• Curved lengths are measured using a thread or measuring tape.
• Every position is described with respect to a reference point.
• Motion depends on the selected reference point.
• Linear motion takes place in a straight line.
• Circular motion takes place along a circular path.
• Oscillatory motion is a repeated to-and-fro movement.
• Periodic motion repeats after equal intervals of time.
• The Earth rotates about its axis and revolves around the Sun.
• Ancient India used units such as Angula, Dhanusa, and Yojana for measurement.

Quick Revision

• Measurement helps us compare objects accurately.
• The SI unit of length is metre (m).
• 1 km = 1000 m.
• 1 m = 100 cm.
• 1 cm = 10 mm.
• Use the correct measuring instrument according to the object.
• Always avoid parallax error while taking readings.
• A reference point helps describe the position of an object.
• An object is at rest if its position does not change.
• An object is in motion if its position changes with time.
• Linear, circular, and oscillatory are the three main types of motion.
• Periodic motion repeats after equal intervals of time.
• Standard units provide accurate and uniform measurements.

Chapter 5. Measurement of Length and Motion

Chapter 5. Measurement of Length and Motion

Measurement is an essential part of science and everyday life. Whether we measure the height of a building, the length of a notebook, or the distance between two cities, accurate measurement helps us obtain reliable and meaningful results. Similarly, understanding motion helps us explain how objects move around us. This chapter introduces the concepts of standard units of length, measuring instruments, correct methods of measurement, reference points, rest, motion, and different types of motion with simple examples.

CBSE Full Notes

Measurement allows us to compare objects accurately using standard units. It is impossible to perform scientific experiments, engineering work, construction, transportation, or trade without proper measurement. Scientists use internationally accepted units so that measurements remain the same everywhere in the world.

Measurement

Measurement is the process of determining the length, height, width, thickness, or distance of an object by comparing it with a standard unit. Accurate measurement helps us perform daily activities efficiently and ensures consistency in scientific observations.

Importance of Measurement

• Helps compare the sizes of different objects.
• Provides accurate and reliable results.
• Essential in science and engineering.
• Used in construction, medicine, sports, and transportation.
• Makes communication of measurements uniform throughout the world.

Ancient Methods of Measurement

Before standard units were introduced, people measured length using different parts of their body such as handspan, cubit, footstep, finger width, and arm length. These methods were simple but not reliable because body sizes differ from person to person.

Limitations of Ancient Units

• Measurements varied from one person to another.
• No uniform standard was available.
• Scientific calculations were not possible.
• Trade and construction became difficult.

Standard Units of Length

To overcome the problems of ancient measurement systems, scientists developed standard units. Today, the International System of Units (SI System) is used throughout the world.

SI Unit of Length

The SI unit of length is the metre (m).

Unit	Relationship
1 kilometre (km)	1000 metres (m)
1 metre (m)	100 centimetres (cm)
1 centimetre (cm)	10 millimetres (mm)
1000 millimetres (mm)	1 metre (m)

Measuring Instruments

Different instruments are used depending upon the size and shape of the object to be measured.

Instrument	Uses
Ruler	Small objects such as pencils, books, and notebooks.
Metre Scale	Tables, benches, doors, and larger objects.
Measuring Tape	Cloth, curved objects, body measurements, and long distances.

Correct Method of Measuring Length

Accurate measurement depends not only on the measuring instrument but also on the correct method of using it.

• Place the measuring scale along the object.
• Keep the zero mark at one end of the object.
• Read the other end carefully.
• Keep your eye vertically above the reading.
• Avoid parallax error.
• Use the smallest suitable unit for greater accuracy.

Using a Damaged Scale

Sometimes the zero mark of a ruler becomes damaged. Such a ruler can still be used accurately.

• Place one end of the object at another clear marking.
• Record the initial reading.
• Record the final reading.
• Subtract the initial reading from the final reading.
• The difference gives the correct length.

Measuring Curved Objects

A rigid ruler cannot measure curved objects directly. In such cases, a thread or measuring tape is used.

Procedure

• Place the thread carefully along the curved path.
• Mark both ends.
• Straighten the thread.
• Measure it using a ruler.

Reference Point

The position of an object is always described relative to another fixed object known as the reference point. Without a reference point, it is impossible to determine whether an object has changed its position.

Examples

• A bus moves with respect to the road.
• A passenger sitting inside the bus is at rest with respect to the bus.
• The same passenger is in motion with respect to the road.

Rest and Motion

An object is said to be at rest if its position does not change with time relative to a reference point. An object is said to be in motion if its position changes with time relative to the chosen reference point.

Rest	Motion
Position does not change.	Position changes with time.
Depends on reference point.	Also depends on reference point.
Example: Book on a table.	Example: Moving bicycle.

Types of Motion

Objects move in different ways depending on their paths.

Linear Motion

Motion along a straight line is called linear motion.

Examples

• Train moving on a straight track.
• Falling stone.
• Person walking on a straight road.

Circular Motion

Motion along a circular path around a fixed point is called circular motion.

Examples

• Blades of a ceiling fan.
• Merry-go-round.
• Hands of a clock.
• Stone tied to a string.

Oscillatory Motion

The repeated to-and-fro motion of an object about its mean position is called oscillatory motion.

Examples

• Simple pendulum.
• Swing.
• Vibrating guitar string.

Periodic Motion

A motion that repeats itself after equal intervals of time is called periodic motion.

Examples

• Oscillation of a pendulum.
• Rotation of Earth about its axis.
• Revolution of Earth around the Sun.
• Hands of a clock.

Applications of Measurement

• Construction of buildings and bridges.
• Manufacturing industries.
• Sports competitions.
• Medical science.
• Scientific research.
• Navigation and transportation.
• Tailoring and garment manufacturing.

Ancient Indian Measurement System

Ancient India developed several units of measurement long before the introduction of modern SI units. Some commonly used ancient units were Angula, Dhanusa, and Yojana. These units demonstrate the advanced understanding of measurement in ancient Indian civilisation.

Remember These Points

• Measurement is essential for accuracy and comparison.
• The SI unit of length is the metre.
• Standard units are accepted worldwide.
• Body-part measurements are not reliable.
• Always use the correct measuring instrument.
• Read the scale vertically to avoid parallax error.
• A damaged ruler can still be used correctly.
• A reference point helps determine rest and motion.
• Motion always depends on the chosen reference point.
• Linear, circular, and oscillatory are the three main types of motion.
• Periodic motion repeats after equal intervals of time.
• Measurement plays an important role in science and everyday life.

Chapter 5. Measurement of Length and Motion

Chapter 5. Measurement of Length and Motion

This assignment is based on the concepts covered in the chapter Measurement of Length and Motion. It includes a variety of competency-based, application-based, and higher-order thinking questions prepared according to the latest CBSE pattern. Students should attempt all questions independently to strengthen their conceptual understanding and improve problem-solving skills.

Assignments - What Have You Learned?

Attempt all the following questions without referring to the textbook. These questions are designed to help you revise the chapter thoroughly and prepare confidently for examinations.

Test Your Learning

Fill in the Blanks

1. The SI unit of length is __________.
2. One metre is equal to __________ centimetres.
3. One kilometre is equal to __________ metres.
4. The position of an object is described with respect to a __________.
5. Motion along a straight line is called __________ motion.
6. The repeated to-and-fro motion of an object is called __________ motion.
7. A motion that repeats after equal intervals of time is called __________ motion.
8. A __________ is used to measure the length of curved objects.
9. Reading a scale from an angle causes __________ error.
10. Body-part measurements are __________ units.

True or False

1. The metre is the SI unit of length.
2. Handspan is a standard unit of measurement.
3. A measuring tape is useful for measuring curved objects.
4. The position of an object can be described without a reference point.
5. A swinging pendulum shows oscillatory motion.
6. The hands of a clock show circular motion.
7. Motion depends on the selected reference point.
8. One centimetre is equal to 100 millimetres.
9. A damaged ruler cannot be used for measurement.
10. Periodic motion repeats after equal intervals of time.

Match the Following

Column A	Column B
Metre	SI unit of length
Reference Point	Determines position
Measuring Tape	Measures curved length
Linear Motion	Straight-line motion
Oscillatory Motion	To-and-fro motion

One Word Answer

1. The SI unit of length.
2. The instrument used to measure curved objects.
3. The fixed object used to describe position.
4. Motion along a straight path.
5. The repeated to-and-fro movement of an object.
6. Motion along a circular path.
7. The error caused by reading a scale from an angle.
8. The internationally accepted system of units.
9. A unit equal to one thousand metres.
10. The motion that repeats after equal intervals of time.

Very Short Answer Questions

1. What is measurement?
2. What is the SI unit of length?
3. Name any two measuring instruments.
4. What is a reference point?
5. Define motion.
6. What is meant by rest?
7. Define linear motion.
8. Define circular motion.
9. Define oscillatory motion.
10. What is periodic motion?

Short Answer Questions

1. Why are standard units of measurement necessary?
2. Differentiate between ancient and standard units of measurement.
3. Explain the correct method of measuring the length of an object.
4. How can a damaged ruler still be used to measure length?
5. Describe how to measure the length of a curved line.
6. Differentiate between rest and motion.
7. Explain the importance of a reference point.
8. Differentiate between linear motion and circular motion.
9. Write any four applications of measurement.
10. Explain periodic motion with suitable examples.

Long Answer Questions

1. Explain the importance of measurement in science and everyday life.
2. Describe the different measuring instruments and their uses.
3. Explain the various types of motion with suitable examples.
4. Discuss the importance of standard units of measurement.
5. Explain the concepts of reference point, rest, and motion with examples.

Case Study Based Questions

Case Study: Riya and Mohan were asked to measure the length of their classroom. Riya used a measuring tape, while Mohan measured it using his footsteps. Both obtained different values. Their teacher explained the importance of using standard units and proper measuring instruments.

1. Why did Riya and Mohan obtain different measurements?
2. Which method is more accurate? Give a reason.
3. What is the SI unit of length?
4. Which measuring instrument should be used for measuring the classroom?
5. Why are standard units preferred over body-part measurements?

Competency Based Questions

1. Measure the length and width of your study table using a metre scale and record your observations.
2. Prepare a chart showing different measuring instruments and their uses.
3. Observe five moving objects around you and classify them as linear, circular, or oscillatory motion.
4. Measure the boundary of a circular plate using a thread and a ruler. Explain your method.
5. List five situations where accurate measurement is essential in daily life.

HOTS Questions (Higher Order Thinking Skills)

1. Why would scientific experiments become unreliable if standard units of measurement did not exist?
2. A passenger sitting inside a moving train says that he is at rest, while a person standing on the platform says that the passenger is in motion. Explain how both statements are correct.
3. Why is a measuring tape preferred over a ruler for measuring curved objects?
4. Imagine a world without standard units of measurement. What problems would people face in trade, construction, and science?
5. Many objects around us show more than one type of motion at the same time. Give two examples and explain your answer.