Boyle's Law Examples in Real Life
What Is Boyle's Law and Equation?
In 1662, Robert Boyle discovered the volume and pressure of gasses are inversely proportionate when held at a constant temperature. Put simply, when volume rises, pressure drops, and vice versa.
The mathematic equation is equally as simple.
PV = k
In this equation, (P) represents pressure, (V) represents volume, and (k) is a constant.
This has become a basic principle in chemistry, now called "Boyle's law," and is included as a special case in the more general ideal gas law.
How Did Boyle Come up With His Law?
Using a vacuum pump invented by Otto von Guericke in 1654, Boyle carried out experiments investigating the properties of air and the vacuum.
During his experiments, he stumbled upon the greatest achievement of his life. By using a J-shaped glass tube that had air at the tip of the curve, Boyle altered the weight of the air using mercury and, as he did so, he saw that the space of air at the tip of the curve became smaller. He discovered that when you increase pressure on a gas, the gas's volume predictably shrinks.
Why Is Boyle's Law Important?
Boyle's law is important because it tells us about the behavior of gasses. It explains, with certainty, that the pressure and volume of gas are inversely proportional to one another. So, if you push on gas, its volume becomes smaller and the pressure becomes higher.
Examples of Boyle's Law in Life
You have probably been well-acquainted with Boyle's law for most of your life without realizing it. We experience examples of this law on a regular basis. The first example is a rather common one, assuming you have filled a tire with air before.
Generally, you fill a tire with somewhere between 30 to 35 PSI (pounds per square inch) of compressed air. This is a measurement of pressure. As you put more and more air into the tire, you are forcing all the gas molecules to get packed together, reducing their volume and increasing the pressure pushing on the walls of the tire. As long as the air temperature remains the same, you are experiencing a real life example of this law.
Other examples include:
Real-World Applications of Boyle's Law
- Spray paint
- The syringe
- The soda can
- The bends
Read on for descriptions of the examples listed above.
1. Spray Paint
While there are a couple different types of aerosol cans, some being a little more elaborate than other, they all rely on the same basic principle: Boyle's law.
Before you spray a can of paint, you are supposed to shake it up for a while as a ball bearing rattles around inside. There are two substances inside the can: one is your product (paint for example), and the other is a gas that can be pressurized so much that it retains a liquid state, even when it is heated past its boiling point.
This liquefied gas has a boiling point far below room temperature. Because the can is sealed, the gas is prevented from boiling and turning into a gas. That is, until you push down the nozzle.
The moment the nozzle of a spray paint can goes down, the seal is broken and the propellant instantly boils, expands into a gas, and pushes down on the paint. Under the high pressure, the paint is forced out of the nozzle as it attempts to reach an area with lower pressure.
2. The Syringe
This mechanism is far more simple than a can of spray paint. Syringes of all types utilize Boyle's law on a very basic level.
When you pull the plunger out on a syringe, it causes the volume within the chamber to increase. As we know, this causes the pressure to do the opposite, which then creates a vacuum. When a syringe is empty, the vacuum within the chamber sucks fluid in through the needle.
3. The Soda Can or Bottle
Typically when we open a bottle of soda, we slowly turn the cap to allow the air to escape before we completely remove the lid. We do this because we've learned over time that twisting it open too fast causes it to fizz up and spill all over. This happens because the liquid is pumped full of carbon dioxide, causing it to bubble up as the CO2 makes its escape.
When a soda bottle is filled, it is also pressurized. Much like the aerosol can mentioned earlier, when you slowly open the cap, the gas is able to increase its volume and the pressure decreases.
Normally you can let the gas out of a can or bottle release cleanly, but if the bottle is shaken up and the gas is mixed into the liquid, then you may have a mess on your hands. This is because the gas trying to escape is mixed into the fluid, so, when it does escape, it brings the foamy fluid out with it. Pressure in the bottle goes down, volume of the gas goes up, and you have yourself a mess to clean up.
4. The Bends
Any properly trained scuba diver knows when they are ascending from deep waters, a slow ascension is critical. Our bodies are built for and accustomed to living in the normal pressure of our lower atmosphere. As a diver goes deeper underwater, that pressure begins to increase. Water is heavy, after all. With the increasing pressure causing a decrease in volume, nitrogen gasses begin to be absorbed by the diver's blood.
When the diver begins his ascent and the pressure is lessened, these gas molecules begin to expand back to their normal volume. With a slow ascent, or through the use of a depressurization chamber, those gasses can work their way back out of the bloodstream slowly and normally. But if the diver ascends too quickly, the blood in their vains becomes a foamy mess. The same thing that happens to a foamy soda is what happens to a diver's bloodstream during the bends. On top of that, any built up nitrogen between the diver's joints will also expand, causing the diver to bend over (hence its name) in severe pain. In the worst cases, this sudden depressurization of the body can kill a person instantly.
The Cartesian Diver: Build Your Own Example of Boyle's Law
By now you either have a basic understanding of Boyle's law and how it can be applied to the real world, or you're suddenly afraid to go swimming.
Either way, this last example of Boyle's law in action is something you can build yourself! First, you need a small list of supplies:
- One transparent 2-liter bottle
- One small glass dropper
Once you've managed to gather these supplies, follow the steps below.
How To Build a Cartesian Diver
- Add water until the 2-liter bottle is full.
- Take your eyedropper, the "diver," and fill it with just enough water so that the top of the dropper is just buoyant enough to float on top of the water.
- Apply the lid to the 2-liter bottle. It must be airtight!
- Squeeze the bottle.
If you have successfully followed the instructions, your Cartesian diver should dive to the bottom as you squeeze the bottle. That's Boyle's law in action!
When you squeeze inward, you are reducing the volume of the bottle. As we know, this reduction in volume increases the pressure.
This increase in pressure pushes against the water, forcing more water up into the eyedropper. This additional water decreases the diver's buoyancy, causing it to "dive" to the bottom. Stop squeezing the bottle, and your diver will ascend back to the water's surface.
DIY Cartesian Diver (Video)
What Is the Ideal Gas Law?
Since it is hard to exactly describe a real gas, scientists created the concept of an ideal gas. The ideal gas law refers to a hypothetical gas that follows the rules listed below:
- Ideal gas molecules do not attract or repel each other. The only interaction between ideal gas molecules would be an elastic collision with each other or with the walls of the container.
- Ideal gas molecules themselves take up no volume. While the gas takes up volume, the ideal gas molecules are considered point particles that have no volume.
There are no gasses that are exactly ideal, but there are many that are close. This is why the ideal gas law is extremely useful when used as an approximation for many situations. The ideal gas law is obtained by combining Boyle's law, Charle's law, and Gay-Lussac's Law, three of the major gas laws.
What Is Charle's Law?
Charle's law, or the law of volumes, was discovered in 1787 by Jaques Charles and states that for a give mass of an ideal gas at constant pressure, the volume is directly proportional to it's absolute temperature. This means that as the temperature of a gas increases, so does its volume.
V / T = k
The equation of Charle's law is written above, with (V) representing volume, (T) representing temperature, and (k) representing a constant.
What Is Gay-Lussac's Law?
Gay Lussac's law, or the pressure law, was discovered by Joseph Louis Gay-Lussac in 1809 and states that, for a given mass and constant volume of an ideal gas, the pressure exerted on the sides of its container is directly proportional to its absolute temperature. This means that pressure indicates temperature.
P / T = k
The equation of Guy Lussac's law is written above, with (P) representing pressure, (T) representing temperature, and (k) representing a constant.
How Does Boyle's Law Relate to Breathing?
When it comes to the effects of Boyle's law on the body, the gas law specifically applies to the lungs.
When a person breathes in, their lung volume increases and the pressure within decreases. Since air always moves from areas of high pressure to areas of low pressure, air is drawn into the lungs.
The opposite happens when a person exhales. Since the lung volume decreases, the pressure within increases, forcing the air out of the lungs to the lower pressure air outside of the body.
What Are the Two Stages of the Breathing Process?
The breathing process, sometimes called respiration, can be simply broken down into two stages: inhalation and exhalation.
During inhalation, also called inspiration, the diaphragm contracts and pulls downward and the muscles between the ribs contract and pull upward, increasing the volume of the lung cavity and decreasing the pressure within. As a result, air rushes in to fill the lungs.
During exhalation, also called expiration, the diaphragm relaxes and the volume of the lung cavity decreases while the pressure within increases. As a result, air is forced out.
How Do You Know When to Breathe?
Breathing is controlled by a respiratory control center at the base of your brain. This center sends signals down your spine that ensure your breathing muscles in your lungs contract and relax regularly.
Your breathing can change depending on how active you are, as well as on the condition of the air around you. Other factors that may affect your breathing include your emotions or deliberate actions such as holding your breath.
A Final Word
I did leave a certain application of Boyle's law out of this list that is used far more than any of the above examples. This system is directly powered by the rules of Boyle's law, and is a device you use every day, everywhere you go.
What is it? Comment your answer below!
© 2012 Steven Pearson