Class 6 Science · Chapter 5 NotesMeasurement of Length and Motion

Measuring length is essential in our daily lives, from buying cloth to measuring the height of a room. People have used various body parts like handspans, fingers, and strides to measure lengths. However, these units vary from person to person, leading to inconsistencies. To avoid this, standard units of measurement are used. The International System of Units (SI) is the standard system adopted worldwide, with the metre (m) as the SI unit of length. A metre scale is commonly used for measurements, where 1 metre is divided into 100 centimetres (cm), and each centimetre is further divided into 10 millimetres (mm).

• Handspans and other body parts vary in size among individuals
• Standard units ensure consistent measurements across different people
• 1 metre (m) = 100 centimetres (cm)
• 1 centimetre (cm) = 10 millimetres (mm)

The International System of Units (SI) provides a standardized way of measuring lengths, ensuring that measurements are consistent and reliable. The metre is the SI unit of length, and it is used globally for various measurements. For larger lengths, such as the distance between cities, the kilometre (km) is used, where 1 kilometre equals 1000 metres. For smaller lengths, like the thickness of a book, centimetres or millimetres are used. This system helps in avoiding confusion and ensures that measurements are universally understood.

• SI system ensures global consistency in measurements
• 1 kilometre (km) = 1000 metres (m)
• Centimetres (cm) and millimetres (mm) are used for smaller measurements
• Units like inch and foot are still used in some contexts

Different measuring instruments are used depending on the object and the required precision. A 15-cm scale is commonly used for measuring smaller objects like pencils and erasers. For larger objects, such as the height of a room, a metre scale or a measuring tape is more appropriate. Flexible measuring tapes are used for measuring curved lengths, like the girth of a tree or the size of a chest. It is important to place the scale correctly along the length of the object and to read the scale from directly above the measurement to ensure accuracy.

• Use a 15-cm scale for smaller objects
• Use a metre scale or measuring tape for larger objects
• Flexible measuring tapes are used for curved lengths
• Place the scale correctly and read it from directly above the measurement

Motion refers to the change in position of an object with respect to a reference point over time. An object is said to be in motion if its position changes, and it is at rest if its position remains unchanged. The reference point is crucial in determining whether an object is in motion or at rest. For example, passengers in a moving bus are at rest with respect to each other but in motion with respect to objects outside the bus. Understanding motion helps in describing the movement of objects in various situations.

• Motion is the change in position of an object with respect to a reference point
• An object is at rest if its position does not change with respect to a reference point
• The reference point is important in determining motion
• Passengers in a moving bus are at rest with respect to each other but in motion with respect to outside objects

Distance is the total path length covered by an object, while displacement is the shortest distance between the initial and final positions. There are different types of motion, including linear motion, where an object moves along a straight line, and circular motion, where an object moves along a circular path. Oscillatory motion occurs when an object moves to and fro about a fixed position, such as a swing or a pendulum. Understanding these types of motion helps in analyzing the movement of objects in various scenarios.

• Distance is the total path length covered by an object
• Displacement is the shortest distance between initial and final positions
• Linear motionmovement along a straight line
• Circular motionmovement along a circular path
• Oscillatory motionmovement to and fro about a fixed position