Identifying Graphical Relationships (Edexcel International A Level Physics)

Identifying Graphical Relationships

• Graphs are used to visualise the relationship between two sets of data from two different variables

• Common relationships are:

  • Directly proportional

  • Inversely proportional

• A direct proportionality relationship is where as one amount increases, another amount increases at the same rate

  • This is represented by a straight-line graph with a positive gradient

• For two variables, y and x this looks like:

y ∝ x

• An inverse proportionality relationship is where as one amount increases, another amount decreases at the same rate

  • This is represented by a curved graph with a decreasing gradient

• For two variables, y and x this looks like:

y ∝ 

Sketched graphs show relationships between variables

• In the first sketch graph, above you can see that the relationship is a straight line going through the origin

  • This means as you double one variable the other variable also doubles so we say the independent variable is directly proportional to the dependent variable

• The second sketched graph shows a shallow curve

  • This is the characteristic shape when two variables have an inversely proportional relationship

• The third sketched graph shows a straight horizontal line,

  • This means as the independent variable (x-axis) increases the dependent variable does not change or is constant