Chapter-Chapter 5. Measurement of Length and Motion Science Curiosity class 6 in english Medium CBSE Notes

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.

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