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# Motion and Measurement of Distances

Story of Transport
In ancient times, people travelled mainly on feet. After domestication of animals human beings started using animals such as horse, camel, elephants etc. The invention of wheel brought about many changes. The invention of steam engine introduced a new source of power and todays electric trains, aero planes etc. are the fastest means of transport.

Measurement
The process of comparing a physical quantity with the standard unit is called measurement.

Standard Unit of Measurement
A fixed value which does not vary from person to person and place to place is called standard unit.

SI Unit of Physical Quantity
It is also known as international system of units or SI units. Full form of SI unit is 'Systeme International d' unites'.

 Physical Quantity SI Units Length Metre (m) Time Second (s) Mass Kilogram (kg) Temperature Kelvin (k)

Measurement of Length
Length is the distance between two point or place. It can be measured using a ruler measuring tape, meter rod etc.

 1 metre (m) = 100 centimeters (cm) 1 centimetre (cm) = 10 millimetres (mm) 1 metre (m) = 1000 millimetres (mm) 1 kilometer (km) = 1000 metres (m) 1 light year = 9, 460, 000, 000, 000, 000 (m) 1 light year = 94, 600, 000, 000, 000 (km)

Rest
If the position of an object remains fixed with respect to the stationary objects in its surroundings then body is said to be in rest.

Motion
If the position of an object changes with respect to the stationary objects in its surroundings then body is said to be in motion.

Types of Motion

• Rectilinear Motion
Movement along a straight line. Ex: Moving car in straight line.
• Circular Motion
Movement along circular path. Ex: Moving of moon around the earth.
• Rotatory Motion
Movement about a fixed axis without changing its position. Ex: A spinning top.
• Periodic Motion
Repetition of motion after regular intervals. Ex: Movement of the earth around the sun.
• Non – Periodic Motion
The motion that does not repeat itself at regular intervals is called non – periodic motion. Ex: Beating of our heart.