A student investigated the effect of temperature on the decay of fresh milk by measuring its pH over a period of 5 days.
The student followed this method:
Table 1 shows the measurements at 18∘C18^\circ\text{C}18∘C: \begin{array}{|c|c|c|c|c|c|c|} \hline \text{Time (days)} & 0 & 1 & 2 & 3 & 4 & 5 \\\ \hline \text{pH} & 6.8 & 6.8 & 6.5 & 5.6 & 4.8 & 4.5 \\\ \hline \end{array}
Answer the following questions:
How could the student keep the milk at a constant temperature of 18∘C18^\circ\text{C}18∘C for 5 days?
Give one variable, other than temperature, that the student should keep constant.
In a graph of these results, with pH on the y-axis and Time on the x-axis, describe how the curve representing the milk at 24∘C24^\circ\text{C}24∘C would compare to the curve for 18∘C18^\circ\text{C}18∘C.