CBSE Physics Subject Notes
There are many objects around us. Some are stationary like trees which are fixed at a place , house, a school, a factory all are stationary objects. On the other hand, a man, animals, birds, cars, buses, train, aero planes … etc do not remain stationary all time. They can move from one place to another. These are called moving objects and the movement of the body is called motion.
A common characteristic of all the moving bodies is that they change their position with time
A body is said to be in motion when its position changes continuously with respect to a stationary object taken as reference point.
Distance: - The distance travelled by a body is the actual length of the path covered by a moving body irrespective of the direction in which the body travels.
Displacement:- When the body moves from one position to another, the shortest distance b/w initial position and the final position of the body along with direction is called displacement.
Note:- distance is a scalar quantity having magnitude only but displacement is vector quantity having magnitude and direction both.
Example - In the same case the displacement is 5 km.
Note – the distance traveled by a moving body can’t be zero but final displacement of the moving body can be zero.
Uniform motion:- A body has uniform motion if it travels equal distance in equal interval of time, no matter how small these time intervals may be.
Non- uniform motion:- A body has non uniform motion if it travels unequal distances in equal interval of time.
For example- if we drop a ball from the roof of a tall building. We find that it covers unequal distances in equal interval of time.
Note: - the distance time graph for a body having non uniform motion is a curved line.
Speed:- speed of a body is the distance travelled by it per unit time.
Speed = distance traveled / time taken
Average speed:- The average speed of a body is the total distance traveled divided by the total time.
Uniform speed:- A body has uniform speed if it travels equal distance in equal interval of time. No matter how small these time intervals may be.
The s.i. unit of velocity is m/s. it is vector quantity
Note:- the direction of the velocity is the same as the direction of displacement of the body.
Uniform velocity:- A body has a uniform velocity if it travels in a specific direction in a straight line and moves over equal distance in equal interval of time, no matter how small these time intervals may be
The velocity can be changed in two ways