Boyle's Law Examples in Real Life
Boyle's Law Explained
In 1662, Robert Boyle discovered that when held at a constant temperature, the volume and pressure of a gas are inversely proportionate. Put simply, when the volume goes up, pressure drops, and vice versa.
The mathematic equation is equally as simple: PV=K where P=Pressure, V=Volume, and K is simply a constant.
This has become a basic principle in chemistry, now called "Boyle's law" and is included as a special case into the more general ideal gas law.
Examples in Real Life
You have probably been well acquainted with Boyle's law for most of your life, and haven't even realized it. We experience examples of it on a regular basis. Several times a day, we might use it as a tool, while we also sometimes recognize it as a killer.
Ever filled up a tire? You will generally fill it to somewhere between 30-35 PSI (Pounds per square inch). 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. As long as the air temperature remains the same, you are experiencing a real life example of this law as you watch your PSI change.
Read on for more examples.
While there are a couple different types of aerosol cans, one being a little more elaborate than the other, they both operate off of the same basic principle: Boyle's law. We'll examine the more elaborate of the two, since it's far more popular.
We know that before you spray a can of paint you are supposed to shake it up for a while, listening as a ball bearing rattles around inside. There are two substances inside the can, one being your product (paint for example), and the other being 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 will be a substance that has a boiling point far below room temperature. The can is sealed, preventing this gas from boiling and turning into a gaseous state. That is, until you push down the nozzle. The moment the nozzle goes down, and the seal is released, there is now an escape route. The propellant instantly boils and expands into a gas and pushes down on the product trying to escape the high pressure, and expand it's volume the atmosphere where there is less pressure. This forces the product to shoot out from the nozzle, and you have a coat of paint.
Did You Know?
The "Ideal Gas Law" was created as a combination of Boyle's law and Charles's law.
This 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 attempting to re-pressurize back to atmospheric levels. Since the only fluid available on the other side of the needle tends to be a liquid such as blood, which gets sucked into the chamber. This then reduces the volume and increases the pressure back to where it wants to be.
The Soda Can
Typically we will take a bottle of soda, slowly turning the cap allowing the air to gradually escape before completely removing the lid. We do this because we've learned over time that popping it open too fast causes it to fizz up and spill all over you and everything around you.
Carbonation is exactly what it sounds like. Water is pumped full of carbon dioxide, causing it to bubble up as the CO2 makes its escape. Throw some syrup into the mix, and you have soda pop. 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 suddenly able to increase its volume in order to decrease the pressure. Since the soda itself is carbonized, the CO2 gasses decide they want to escape as well, and you have your fizz.
All is fine and dandy, until you shake the bottle up. Shaking up the bottle causes that neat pocket of carbon dioxide gas in the top to mix in with the soda. Now, pop the cap off. Suddenly all of these excess gas bubbles within the soda want to expand and escape their high pressure environment as well. Rather than being able to expand and shoot out of that neat pocket of air with a "pffffffft," they expand while they're still in the soda. As it tries to muscle its way out, it pushes the soda along with. Pressure in the bottle goes down, volume of the gas goes up, and you have yourself a mess to clean up.
Any properly trained scuba diver knows that 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 increase in pressure causing a decrease in volume, nitrogen gasses begin absorbing into the diver's blood.
When the diver begins his ascent, 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 as they return to their normal volume. Ascend too quickly, however, and his blood becomes a foamy mess. Remember what happens when carbon tries to escape the soda? That same thing is happening in the poor diver's bloodstream. On top of that, any built up nitrogen between the diver's joints will also want to expand. This causes the diver to bend over (where it gets the name) and experience severe pain. In more severe cases, this sudden depressurization of the body can kill a person instantly!
The Cartesian Diver: Build Your Own Boyle's Law
- By now you either have a basic understanding of Boyle's law and how it can be applied in 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! Don't worry, it's simple. First you will need a small list of supplies:
- One 2-liter bottle (clear)
- One small glass dropper
Many don't have the money or time to acquire these supplies. If you fall into that category, you may be able to sell a few things on eBay that have been lying around in a box or attic. Or in a box in the attic.
Once you've managed to gather these supplies, it would be advised to find a handyman or somebody skilled in construction/engineering to assist in deciphering the following steps:
- Fill the 2 liter bottle between 2/3 and 3/4 full of water.
- Take your eyedropper, the "diver," and fill it with just enough water so that the top of the dropper is just buoyant enough to tread the water.
- Apply the lid to the 2 liter bottle. It must be airtight!
- Squeeze the bottle.
If you have successfully followed the instructions, good for you. 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 of all of the gas, including what is contained in your eyedropper.
This increase in pressure pushes against the water, forcing more water up into the eyedropper. As you can see, this additional water decreases the diver's buoyancy, causing it to "dive" to the bottom. Stop squeezing the bottle and everything returns to normal, allowing your diver to ascend back to the water's surface. You would be keen to let go slowly, so your diver doesn't ascend too quickly. Wouldn't want it getting the bends!
One More Thing...
I did leave a certain system 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 it is a device you use every day, everywhere you go.
What is it?
Comment below, let me know!
© 2012 Steven Pearson