Fundamentals 5 Since the basic unit for area is m 2 , then areas quoted in other units should ﬁ rstly be converted into square metres before calculations proceed. This procedure applies to all the derived units, and it is good practice to convert all quantities into their ‘ basic ’ units before proceeding with calculations. It is left to the reader to conﬁ rm that the following conversions for volumes are correct: 11011039363mmmcmm .3 Worked Example 1.3 Q A mass m of 750 g is acted upon by a force F of 2 N. Calculate the resulting acceleration given that the three quantities are related by the equation F ma newton A m 750 g 0.75 kg; F 2 N Since newton, thenmetre/secondso m/FmaaFma220752 667..ss 2 Ans 1.5 Graphs A graph is simply a pictorial representation of how one quantity or variable relates to another. One of these is known as the dependent variable and the other as the independent variable. It is general practice to plot the dependent variable along the vertical axis and the independent variable along the horizontal axis of the graph. To illustrate the difference between these two types of variable consider the case of a vehicle that is travelling between two points. If a graph of the distance travelled versus the time elapsed is plotted, then the distance travelled would be the dependent variable. This is because the distance travelled depends on the time that has elapsed. But the time is independent of the distance travelled, since the time will continue to increase regardless of whether the vehicle is moving or not. Such a graph is shown in Fig. 1.2 , from which it can be seen that over the ﬁ rst three hours the distance travelled was 30 km. Over the next two hours a further 10 km was travelled, and subsequently no further distance was travelled. Since distance travelled divided by the time