- A frame in which an observer is situated and makes his observations is known as his ‘Frame of reference’.
- The reference frame is associated with a co-ordinate system and a clock to measure the position and time of events happening in space. We can describe all the physical quantities like position, velocity, acceleration etc. of an object in this coordinate system.
- Frame of reference are of two types : i.e. Inertial frame of reference & Non-inertial frame of reference,
Inertial frame of Reference
- A frame of reference which is at rest or which is moving with a uniform velocity along a straight line is called an inertial frame of reference.
- In inertial frame of reference Newton’s laws of motion holds good.
- Inertial frame of reference are also called unaccelerated frame of reference or Newtonian or Galilean frame of reference.
- Ideally no inertial frame exist in universe. For practical purpose a frame of reference may be considered as inertial if it’s acceleration is negligible with respect to the acceleration of the object to be observed.
- To measure the acceleration of a falling apple, earth can be considered as an inertial frame.
- To observe the motion of planets, earth can not be considered as an inertial frame but for this purpose the sun may be assumed to be an inertial frame.
The lift at rest, lift moving (up or down) with constant velocity, car moving with constant
velocity on a straight road.
Non inertial frame of reference :
- Accelerated frame of references are called non-inertial frame of reference.
- Newton’s laws of motion are not applicable in non-inertial frame of reference.
- Example : Car moving in uniform circular motion, lift which is moving upward or downward with some acceleration, plane which is taking off.