Graphs to understand the basics

1. Graphs
Graphs
Make it
Make it
easy……
easy……

2. Contents
• 1. Reading Graphs
1. Reading Graphs
• 2. Gradient
2. Gradient
• 3. Plotting Graphs
3. Plotting Graphs

3. 1. Reading Graphs
• Graphs in Physics will have lines
that are either straight-lines or
smooth-curves.
• Graphs may, however, consist of
several of these lines.
• Some will pass through the
origin (0,0), some will not.

6.  1. Reading Graphs
1. Reading Graphs
(completed)
(completed)
 2. Gradient
2. Gradient
 3. Plotting Graphs
3. Plotting Graphs

7. 2. Gradient
Calculating the Gradient of a
Straight-Line Graph
We can measure the slope
(gradient) of the line and express
it as a number.

8.  Choose two points (P1 and P2) one
near to each end of the graph.

9.  Mark out a large triangle using the
two points you have chosen.

10.  To find the gradient we use the formula

11. Calculating the Gradient
of a Smooth-Curve Graph

12.  Choose the point
at which you
wish to find the
gradient.
 Draw a tangent
to the line at the
chosen point.
 Draw a triangle
using the
tangent and
calculate the
gradient.

13.  1. Reading Graphs
1. Reading Graphs
(completed)
(completed)
 2. Gradient (completed)
2. Gradient (completed)
 3. Plotting Graphs
3. Plotting Graphs

14. 3. Plotting Graphs
Graphs are plotted to show the
relationship between two quantities. The
quantity that you control and change is
usually plotted on the x-axis. You should
vary this quantity in regular steps in the
experiment. The quantity that is
dependent on the quantity that you
control or change is plotted on the y-axis.

15. The following points should be
noted when drawing graphs.

16. Label both axes prominently with the
names and units of the variables. The SI
method is recommended e.g. “x/m” or “I/A”
etc.
Give a title to the graph.
Use a convenient scale to draw the graph
as large as available space allows.

Avoid using “3-scales” and other awkward
scales. Such scales usually lead to errors in
plotting and reading from the graph.

The paper can be placed either in the
landscape or portrait position.

17. Do not attempt to join all of the points on
the graph. It is not likely that you would
obtain a straight line or a smooth curve.
Rather, use a transparent ruler to help you
draw the best straight line or a flexi-curve
to draw a smooth curve through most of
the points.
When determining the gradient of a
straight line, draw a large triangle and use
the co-ordinate method to determine the
gradient.

18. Evidence of how a reading is obtained from
the graph must be shown.

When finding the gradient ensure that a triangle
is drawn on the graph paper.

Reference lines to find a point on the horizontal
axis corresponding to a point on the vertical axis
or vice-versa.

19.  The following two diagrams show
good examples of straight-line and
smooth-curve graphs.
 Notice how the lines do not pass
through every point but pass close to
all of the points.
Tips…...

20. Straight-line graph

21. Smooth-curve graph

22.  1. Reading Graphs
1. Reading Graphs
(completed)
(completed)
 2. Gradient (Completed)
2. Gradient (Completed)
 3. Plotting Graphs
3. Plotting Graphs
(Completed)
(Completed)