Motion and Measurement of Distances : Invention of the wheel made a great change in modes of transport.

The invention of the steam engine led to the development of new means of transport. The early years of 1900 saw the development of aero planes.

Electric trains, monorail, supersonic aero planes and spacecraft are some of the contributions of the 20th century.

STANDARD UNITS OF MEASUREMENTS :-  

In ancient times, the length of a foot, the width of a finger, and the distance of a step were commonly used as different units of measurements.

In ancient India, small length measurements used were an angul (finger) or a mutthi (fist).

In 1790, the French created a standard unit of measurement called the metric system.

For the sake of uniformity, scientists all over the world have accepted a set of standard units of measurement. The system of units now used is known as the International System of Units (SI units). The SI unit of length is a metre.

Motion:–  Movement of objects

Types of Motion:-

• Rectilinear:- The objects move along a straight line. This type of motion is called rectilinear motion.
• Circular Motion:- The objects moving along a circular path known as circular Motion.
• Periodic Motion:- an object repeats its motion after some time. This type of motion is called periodic motion. A branch of a tree moving to and fro , motion of a child on a swing, strings of a guitar or the membrane of drums (tabla) being played, are all examples of periodic motion.