Frame of Reference Physics Notes
The Frame of Reference:
Imagine you threw and caught a ball while you were on a train moving at a constant velocity passing a station. To you, the ball appears to simply travel vertically up and then vertically down under the influence of gravity. However, to an observer standing on the station platform, the ball would appear to travel in parabola, with a constant horizontal component of velocity equal to the velocity of the train. This is illustrated in the figure below.
Path of the ball as seen by an observer on the train and on at the station
The different observations occur because the two observers are in different frames of reference.
Thus, a frame of reference is a set of coordinates that can be used to determine positions and velocities of objects in that frame. Different frames of reference move relative to one another.
Frames of reference can be of two types:
(a) Inertial frame of reference
(b) Non-inertial frame of reference.
(a) Inertial frame of reference: A frame of reference that remains at rest or moves with constant velocity with respect to other frames of reference is called inertial frame of reference. An inertial frame of reference has a constant velocity. That is, it is moving at a constant speed in a straight line, or it is standing still. Newton’s laws of motion are valid in all inertial frames of reference. Here, a body does not change due to external forces. All inertial frames of a reference are equivalent for the measurement of physical phenomena.
There are several ways to imagine this type of motion:
- Motion of Earth
- A space shuttle moving with constant velocity relative to the earth.
- A rocket moving with constant velocity relative to the earth.
(b) Non-inertial frame of reference: A frame of reference is said to be the non-inertial frame of reference when a body, not acted upon by an external force, is accelerated. In a non-inertial frame of reference, Newton’s laws of motion are not valid. It also does not have a constant velocity and is accelerating. There are several ways to imagine this type of motion.
- The frame could be travelling in a straight line, but the speed of the object increases or decrease.
- The frame could be travelling along a curved path at a steady speed.
- The frame could be travelling along a curved path and also the speed of the object increases or decrease.
- To locate the position of a particle, the frame of reference should be universally accepted and is easily available.
The simplest reference frame is the cartesian frame of reference or cartesian coordinate system. It has three mutually perpendicular axes named as 1,7 and Z axes. The point of intersection of these axes is called origin (O) and is considered as the reference point
The X, Y and Z coordinates describe the position of the object with respect to the coordinate system. To measure time, put a clock in the system.
There are two types of frames of reference of the co-ordinate system.
1. Anticlockwise co-ordinate system
(a): Anticlockwise Reference System
2. Clockwise coordinate system:
Generally, we use clockwise coordinate system.
(b): Clockwise Reference System