2.1 REST AND MOTION
We see different things around us. Some of them are very still while others are in movement.
A body is said to be very still, in the event that it doesn’t change its position as for its environment.
Surroundings are the spots in its neighborhood where different items are available. Correspondingly,
A body is said to be in movement, on the off chance that it changes its position as for its environment.
The condition of rest or movement of a body is relative. For instance, a traveler sitting in a moving transport is very still since he/she is not evolving his/her position concerning different travelers or items in the transport. Be that as it may, to a spectator outside the transport, the travelers and the articles inside the transport are in movement.
2.2 TYPES OF MOTION
If we observe carefully, we will find that everything in the universe is in motion. However, different objects move differently. Some objects move along a straight line, some move in a curved path, and some move in some other way. There are three types of motion.
(i) Translatory motion (linear, random and circular)
(ii) Rotatory motion
(iii) Vibratory motion (to and fro motion)
Watch how various objects are moving. Do they move along a straight line? Do they move along a circle? A car moving in a straight line has translational motion. Similarly, an aeroplane moving straight is in translational motion.
In translational motion, a body moves along a line without any rotation. The line may be straight or curved.
We come across many objects which are moving in a straight line. The motion of objects such as a car moving on a straight and level road is linear motion.
Straight line motion of a body is known as its linear motion.
Aeroplanes flying straight in air and objects falling vertically down are also the examples of linear motion.
A stone tied at the end of a string can be made to whirl. What type of path is followed by the stone? The stone as shown in figure 2.6, moves in a circle and thus has circular motion.
Have you noticed the type of motion of insects and birds? Their movements are irregular.
The disordered or irregular motion of an object is called random motion.
Thus, motion of insects and birds is random motion. The motion of dust or smoke particles in the air is also random motion. The Brownian motion of a gas or liquid molecules along a zig-zag path such as shown in figure 2.8 is also an example of random motion.
Study the motion of a top. It is spinning about an axis. Particles of the spinning top move in circles and thus individual particles possess circular motion. Does the top possess circular motion?
2.3 SCALARS AND VECTORS
In Physics, we come across various quantities such as mass, length, volume, density, speed and force etc. We divide them into scalars and vectors.
A physical quantity which can be completely described by its magnitude is called a scalar. The magnitude of a quantity means its numerical value with an appropriate unit such as 2.5 kg, 40 s, 1.8 m, etc. Examples of scalars are mass, length, time, speed, volume, work and energy.
A scalar quantity is described completely by its magnitude only.
A vector can be described completely by magnitude alongwith its direction. Examples of vectors are velocity, displacement, force, momentum, torque, etc. It would be meaningless to describe vectors without direction. For example, distance of a place from reference point is insufficient to locate that place. The direction of that place from reference point is also necessary to locate it.
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