Everything Science Grade 10

21.2 CHAPTER 21. MOTION IN ONE DIMENSION

For example, if you were in a
classroom and wanted to tell
a classmate where you were
standing you would first give
them a reference point. The ref-
erence point might be the class-
room door. You would then be
able to say that you are 2 m
from the doorway. This still
doesn’t give your position pre-
cisely. We need to provide a
reference point and a coordi-
nate system to use to define the
location precisely.

Describing your location

Photograph by chokola on Flickr.com

Then you can say that you are, for example, 2 m from the door directly inside the classroom.
The classroom door is a reference point and inside/outside is the coordinate system you
have chosen. A frame of reference orreference frameis reference point which serves as
the origin for a coordinate system. The coordinate system can be up or down, inside or
outside, left or right or even forward or backward. These are all examples that define a 1-
dimensional coordinate system. We choose one of the directions as thepositivedirection.

DEFINITION: Frame of reference

A frame of reference is a reference point combined with a set of directions.

A graphical representation of a 1-dimensional frame of reference:

~xi

x

origin

b

negative (–) direction positive (+) direction

Figure 21.1: Frame of reference

You can define different frames of reference for the same problem but the outcome, the
physical results, will be the same. For example, a boy is standing still inside a train as it
pulls out of a station. Both you and the boy define your location as the point of reference
and the direction train is moving as a where you are standing as the point of reference and
the direction the train is moving in as forward.

388 Physics: Mechanics