Motion Class 9 Notes Science Chapter 8

Stationary Object:-The object which remains Fixed at a place is called Stationary object.

E.g:-Trees, a house, a school, a factory

Moving Object:- The object which can move from one place to another is called moving object.

E.g:- a man moves when he walks along a road, a bird moves when it flies in   the sky etc….

Note:- A common characterstics of all the moving bodies is that they change their position with time.

Reference Point:- A body is said to be in motion (or moving) when its position changes contiously with respect to a stationay object taken as reference point.   

Note:-If a body moves fairly fast, then its movement(or motion) can be observed easily. But if a body moves very slowly, the it become difficult to observe its movement immediately.

               E.g:- A wrist watch has three hands:- a second hand, a minute hand and an hour hand, which moves round and round on the dial of the watch. Now, the seconds’ hand of watch moves quite fast, so we can observe the movement of the second hand of watch very easily. But the minutes hand and an hour hand of a watch moves quite slowly, so their movement cannot be observed easily.

Motion:- The body is said to be in motion when its position changes continuously with respect to time.

Note:- Physical quantity:- The quantity which can be measured or quantities of Physics

E.g. The quantity like distance, displacement, etc. are known as physical quantity.

Scalar Quantity:- A physical quantity having only magnitude( or size) is known as a scalar quantity.

E.g:- Distance, speed, mass, length, time

Vector Quantity:- A physical quantity having magnitude as well as direction is called vector quantity.

E.g:- Displacement, velocity, acceleration, force, moventum, torque, Angular movementum

Distance Travelled and Displacement

Distance(‘D’):- 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.

E.g:- In this case, the actual length of the path covered by the man is 5km+3km=8km, so the distance travelled by the man is 8km.                                      

Note:- If we a round trip and reach back at the starting point then, though we have travelled some distance, our final displacement will be zero. This is because the straight line distance between the initial and final position will be zero.