# How do you graph Boyle's law?

##### 1 Answer

**WARNING! Long answer!** Boyle’s Law examines the relationship between the volume of a gas and its pressure.

#### Explanation:

So, you would do an experiment in which you measure the volume of a gas at various pressures.

A common lab experiment uses a pop can with various amounts of water to compress the air in a syringe.

(Adapted from dwb5.unl.edu)

Let’s assume you get the following data.

The best way to determine a relationship is to plot a graph that gives a straight line.

Since the pressure is directly proportional to the mass of the can plus water, we can use the mass instead of pressure.

At this point we (theoretically) don’t know the relationship, so we plot

We plot pressure as the independent variable (along the horizontal or

You could do this by hand, but it is more convenient to use a computer to do the job for you.

Your graph looks like a hyperbola, as in the diagram above.

The equation for a hyperbola is

It looks as if we should try a plot of

We calculate the values of

We get the straight line plot shown below.

You can extend the line backwards until it reaches

If you use a computer or a calculator, you can tell it to calculate the equation for the line that best fits all the points (the regression line).

My computer tells me that the equation is

The graph of

This means that the measured volume is **inversely proportional** to the pressure — **Boyle's Law**.