Page 271 - CITS - ED - Mechanical

ENGINEERING DRAWING - CITS

EXERCISE 11 : Graph & Charts

Graph & Charts

Concept
Representation of the relationship between two variable quantities on a squared paper known as graph paper is
referred as plotting of graphs. A dependent variable is the one which depends upon another variable called the
independent variable. For example in a graph showing the relationship between the speed and time of a car that
is moving to cover a certain distance, the speed is the independent variable and the time is the dependent vari-
able.(Fig 1)

Fig 1

Axis and quadrants
‘x’ axis is the horizontal line drawn on the graph sheet, to represent the independent variable by means of a conve-
niently chosen scale. The ‘y’ axis is the vertical line drawn on the graph sheet, to represent the dependent variable
by means of a conveniently chosen scale. The point of intersection of the two axes is called as the origin.(Fig 2&3)

Fig 2 Fig 3

To plot the graph to represent the two variables, which may have both positive both negative, positive and nega-
tive values, the graph sheet is conveniently divided into four quadrants and the origin is also conveniently fixed.
To plot positive and negative values of ‘x’ and ‘y’, the two variables the rule is

+ve values of ‘x’: to the right of the origin along the horizontal axis.
-ve values of ‘x’: to the left of the origin along the horizontal axis.
+ve values of ‘y’: above the origin along the vertical axis.
-ve values of ‘y’: below the origin along the vertical axis.

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