Study of motion _________________________________________________________________________________________________________________________________________________________________________________________________________
2. Position Figure 8.10 Reference frame. 2D
Motion can be defined as change in position, so, in order to describe the motion of an object, you must first be able to describe its position—where it is at any particular time. More precisely, you need to specify its position relative to a convenient reference frame.
A reference frame is a point or a set of coordinates that can be used to determine positions and velocities of objects in that frame.
Earth is often used as a reference frame, and we often describe the position of an object as it relates to stationary objects in that reference frame.
For example, a rocket launch would be described in terms of the position of the rocket with respect to the Earth as a whole, while a teacher’s position could be described in terms of where she is in relation to the nearby white board.
In other cases, we use reference frames that are in motion relative to the Earth.
To describe the position of a person in an airplane, for example, we use the airplane, not the Earth, as the reference frame. Figure 8.11 Reference frame. 1D
The positionof a body is the place where it is with respect to a reference frame. It is given in terms of the distance, in a straight line, between the body and the point taken as the origin of the reference frame.
Depending of the type of movement, we can choose reference frames in 1D, 2D or 3D.