How do we know something is true? In grade school, you may remember being taught a process by which an observation elicits a question, from which a hypothesis can be derived, which leads to a prediction that can be tested, and proven…or not) These steps are commonly known as the Scientific Method, and they’ve been successfully used for thousands of years, by such legendary people of science as Aristotle (384 – 322 BC,) Roger Bacon (1219 – 1292,) Johannes Kepler (1571-1630,) Galileo Galilei (1564-1642) and right up to today’s scientists who run the CERN Large Hadron Collider. The collider is the largest machine in the world, and its very purpose is the testing and proving (or not) of hypotheses based on questions that come from observations (often made in the LHC itself) in ongoing efforts to answer amazingly complex questions regarding space, time, quantum mechanics, and general relativity.

The Scientific Method is actually the reason (more on this in a minute) for the name of a fundamental law of physics: Boyle’s Law. It states:

“For a fixed amount of an ideal gas kept at fixed temperature, pressure and volume are inversely proportional.”

And can be mathematically represented:

**PV=k**, where:

**P =** is the pressure of a gas
**V =** is the volume of that gas, and
**k =** is a constant

So, if “k” is held constant, no matter how pressure changes, volume will change in inverse proportion. Or, if volume changes, pressure will change in inverse proportion. In other words, when one goes up, the other goes down. It’s also quite useful in another formulaic representation, which allows us to calculate the resultant volume (or pressure,) assuming the initial volume & pressure and resultant pressure (or volume) is known:

**P**_{1}V_{1}=P_{2}V_{2}, where:

**P**_{1 }and **P**_{2} are the initial, and resultant, pressures (respectively) and
**V**_{1 }and **V**_{2} are the initial, and resultant, volumes (respectively)

This is in fact, what happens when compressed air is generated, so this formula is instrumental in many aspects of air system design, such as determining compressor output, reservoir storage, pneumatic cylinder performance, etc.

Back to the reason it’s called “Boyle’s Law” – it’s not because he discovered this particular phenomenon. See, in April of 1661, two of Robert Boyle’s contemporaries, Richard Towneley and Henry Power, actually discovered the relationship between the pressure and volume of a gas when they took a barometer up & down a large hill with them. Richard Towneley discussed his finding with Robert Boyle, who was sufficiently intrigued to perform the formal experiments based on what he called “Mr Towneley’s hypothesis.” So, for completing the steps of Scientific Method on this phenomenon – going from hypothesis to law – students, scientists, and engineers remember Robert Boyle.

Russ Bowman

Application Engineer

EXAIR Corporation

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IMGP6394 image courtesy of Matt Buck, Creative Commons License

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