Scuba divers (ultramarinfoto, iStockphoto)
Scuba divers (ultramarinfoto, iStockphoto)
There are four laws, known as Gas Laws, which describe how gases behave. The four laws are Boyle’s Law, Charles’s Law, Gay-Lussac’s Law and Avogadro’s Law. Boyle’s LawRobert Boyle, a famous English chemist, discovered in 1662 that if you pushed on a gas, its volume would decrease proportionately. For example, if you doubled the pressure on a gas (increase the pressure two times), its volume would decrease by half (decrease the volume two times). The opposite is also true. If you reduced the pressure on a gas by 3.5 times, then its volume would increase by 3.5 times. This law is an example of an inverse relationship - if one factor increases, the other factor decreases. Relationship between pressure and volume of a gas (©2020 Let’s Talk Science). Image - Text Version
Pulling up on the lid of a sealed container increases the volume and decreases the pressure. Pushing down on the lid of a sealed container decreases the volume and increases the pressure. Boyle’s Law in Everyday LifeHere’s a story from British Airways. Back when British Airways was called British Overseas Airways Corporation (BOAC) (before 1974), female flight attendants in the airline were finding that their uniform skirts were fitting on take-off but once they reached cruising altitude, their skirts felt too tight. This tight-skirt mystery was solved using gas laws! A spokesman for BOAC used Boyle’s Law to explain what was going on. He explained that as the pressure in the cabin decreased at the higher altitude, the pressure in the flight attendants’ stomachs also decreased, thus causing the volume of their stomachs to increase (making their stomachs bulge). Since then, female flight attendants wear adjustable skirts. The working of a syringe can also be explained using Boyle’s Law. When the plunger of a syringe is pulled out, the volume inside the barrel increases, resulting in a decrease in the pressure inside the barrel. Fluids (such as water) flow from a high pressure area to a low pressure area. This means that once the pressure inside a syringe is lower than the pressure outside the syringe, a fluid near the needle (e.g., water, medicine, etc.) will flow into the syringe. Parts of a syringe (Let’s Talk Science using an image by Biggishben via Wikimedia Commons).The opposite is also true. When the plunger is pushed back in, the volume decreases and the pressure increases. Once the pressure is greater than that outside the syringe, the fluid inside the barrel will flow out. The operation of your lungs also can be explained using Boyle’s Law. When you inhale (breathe in), your diaphragm (a large muscle below your lungs) lowers, which increases the volume inside your lungs. This makes the air pressure inside your lungs lower than the air pressure outside your lungs (and your body); therefore, the outside air is drawn into your lungs (much like the syringe). When you exhale (breathe out), your diaphragm pushes upwards, reducing the volume inside your lungs, increasing the pressure and forcing the air outwards. A: Inhalation (breathing in) and B: expiration (breathing out) (Let’s Talk Science using images by LadyofHats on Wikimedia Commons (A) and Wikimedia Commons (B)).A weather balloon is a special type of high altitude balloon. These balloons can reach heights of 18 to 37 km above the Earth carrying instruments for measuring atmospheric pressure, temperature and wind among other things. When weather balloons are sent up, they are only partly filled with gas (typically with helium). Why don’t they fill them completely? Short answer – because they would pop! At higher elevations, the air pressure outside the balloon is lower than the pressure of the helium inside the balloon. As Boyle’s Law states, this causes the volume inside the balloon to increase. If the balloon was already full, this increase in volume could cause the balloon’s rubber to stretch beyond its breaking point. A U.S. Navy weather balloon (Source: U.S. Navy photo [public domain] via Wikimedia Commons).
When the plunger of the syringe was pulled out the pressure decreases so th volume increases, this can be related to the appearance of the marshmallow wherein it gets smaller when plunger was pushed in that increases the pressure and its becomes big in the absence of pressure or when the plunger was pulled out Bring Science Home A pressure-filled science project from Science Buddies
Key Concepts Physics Gas Pressure Volume Boyle's Law Introduction Background You can observe a real-life application of Boyle's Law when you fill your bike tires with air. When you pump air into a tire, the gas molecules inside the tire get compressed and packed closer together. This increases the pressure of the gas, and it starts to push against the walls of the tire. You can feel how the tire becomes pressurized and tighter. Another example is a soda bottle. To get carbon dioxide gas into the liquid, the whole bottle is usually pressurized with gas. As long as the bottle is closed, it is very hard to squeeze, as the gas is confined to a small space and pushes against the bottle's walls. When you remove the cap, however, the available volume increases and some of the gas escapes. At the same time its pressure decreases. One important demonstration of Boyle's law is our own breathing. Inhaling and exhaling basically means increasing and decreasing the volume of our chest cavity. This creates low pressure and high pressure in our lungs, resulting in air getting sucked into our lungs and leaving our lungs. In this activity you will create your own demonstration of Boyle's law. Materials
Observations and Results The results look different with the water-filled balloon. Although you are compressing the air inside the syringe when pressing on the plunger, the water inside the balloon does not get compressed. The balloon stays the same size. The water balloon also keeps its shape when pulling out the plunger while closing the tip of the syringe. In contrast to gases, liquids are not compressible as their particles are already very close together. Boyle's law only applies to gases. If you filled the syringe with water as well, you should still have seen the air-filled balloon shrinking while pushing the plunger into the syringe. The air-filled balloon also should have expanded when pulling the plunger out while the tip of the syringe was closed. You might have noticed, though, that you were not able to push and pull the plunger in and out as far as you could with the air-filled syringe. This is again because of the fact that liquids cannot be compressed like gases. You should have observed that also when trying to push the plunger in or pull it back in the water-filled syringe with the water-filled balloon. It was probably impossible to move the plunger in and out! More to Explore This activity brought to you in partnership with Science Buddies Discover world-changing science. Explore our digital archive back to 1845, including articles by more than 150 Nobel Prize winners. Subscribe Now! |