History Of Transport:
Long ago people did not have any means of transport. They used to move only on foot and carry goods either on their back or using animals.
For transport along water routes, boats were used from ancient times. To begin with, boats were simple logs of wood in which a hollow cavity could be made. Later, people learnt to put together different pieces of wood and give shapes to the boats. These shapes imitated the shapes of the animals living in water.
Invention of the wheel made a great change in modes of transport. The design of the wheel was improved over thousands of years. Animals were used to pull vehicles that moved on wheels. Until the beginning of the 19th century, people still depended on animal power to transport them from place to place. The invention of steam engine introduced a new source of power. Railroads were made for steam engine driven carriages and wagons.
Later came automobiles. Motorised boats and ships were used as means of transport on water. The early years of 1900 saw the development of aeroplanes. These were later improved to carry passengers and goods. Electric trains, monorail, supersonic aeroplanes and spacecraft are some of the 20th century contributions.
Measurements:
Measurement means the comparison of an unknown quantity with some known quantity. This known fixed quantity is called a unit . The result of a measurement is expressed in two parts. One part is a number. The other part is the unit of the measurement.
In ancient times, people used length of a foot, the width of a finger, the distance of a step as units of measurement. This caused confusion and a need to develop a uniform system of measurement arose.
Standard Units Of Measurement:
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.
Correct Measurement of Length:
For measuring the length of an object, you must choose a suitable device. You cannot measure the girth of a tree or the size of your chest using a metre scale, for instance. Measuring tape is more suitable for this.
Correct position of the eye is also important for taking measurement. Your eye must be exactly in front of the point where the measurement is to be taken.
Motion and their types:
Motion is a change in the position of an object with time.
When objects move along a straight line, this type of motion is called rectilinear motion . Motion of a vehicle on a straight road, march-past of soldiers in a parade or the falling of a stone are some examples of rectilinear motion.
In circular motion an object moves such that its distance from a fixed point remains the same. The motion of a point marked on the blade of an electric fan or the hands of a clock are examples of circular motion.
In some cases, an object repeats its motion after some time. This type of motion is called periodic motion Motion of a pendulum, a branch of a tree moving to and fro, motion of a child on a swing, strings of a guitar or the surface of drums (tabla) being played, are all examples of periodic motion .
Have you observed a sewing machine?
It remains at the same location while its wheel moves with a circular motion. It also has a needle that moves up and down continuously, as long as the wheel rotates. This needle is undergoing a periodic motion.
Have you observed closely, the motion of a ball on the ground?
Here the ball is rolling on the ground – rotating as well as moving forward on the ground. Thus, the ball undergoes a rectilinear motion as well as rotational motion.
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