How to Teach Kids About Air Pressure
August 15, 2019
Although we rarely think about it, air surrounds us at all times and exerts a force on every inch of our bodies. This force, known as air pressure, is one of the most important topics in science, as it explains weather patterns, how airplanes fly and a variety of other wonders. In case you’re planning on teaching kids about air pressure, we’ve provided you with an explanation of the basics and some simple, fun and engaging experiments to demonstrate the power of this natural phenomenon.
What Is Air Pressure?
The term “air pressure” is used in reference to the weight of air molecules pressing down on the earth. At sea level, air pressure is generally 14.7 psi (pounds per square inch), which means that 14.7 pounds are pressing down on every square inch of our bodies. The reason we can still move our bodies freely is because the air is exerting pressure on us in all directions, and the reason we aren’t crushed is because the air pressure inside our bodies is the same.Air pressure is determined by the following three factors:
- Temperature: As air gets warmer, it expands. This expansion causes the density of the air to decrease, which results in lower pressure. When air gets colder, on the other hand, it shrinks. This shrinking causes the air to become denser, which leads to higher pressure. This phenomenon is why areas near the equator, which are hot, generally have low air pressure, and areas near the North and South Poles, which are cold, have high air pressure.
- Altitude: The higher you are above sea level, the less dense the air is. As less dense air weighs less, it produces lower air pressure, which is why it can be difficult to breathe on top of a tall mountain. It also explains why your ears will pop when you’re going up or down a mountain in a car — your inner ear has air trapped in it, and as the air pressure outside decreases, the air trapped in your ear will cause the eardrums to push outward. This expansion is what causes the “pop.”
- Moisture: The amount of moisture in the air also affects the density of the air and, therefore, the air pressure. Water vapor is a light gas compared to the gases that make up the atmosphere, which is primarily oxygen and nitrogen. So when the moisture in the atmosphere increases, the amount of nitrogen and oxygen decreases per unit of volume, which causes the density of the air to decrease.
Differences in Air Pressure Cause Movement
One of the most interesting aspects of air pressure is that when a pocket of air pressure is changed, things begin to move. This pressure difference that creates movement is what causes wind, tornadoes and many other weather phenomena.
When you’re discussing the movement of air, keep in mind that scientists speak in terms of the higher pressure “pushing” things, not lower pressure “pulling” things.
How to Measure Air Pressure
Air pressure is commonly measured using a mercury barometer. A mercury barometer contains a column filled with mercury, and the higher the air pressure is, the higher the column of mercury will be. By measuring the height of the column, you can determine the air pressure.
These days, it’s more common to use a digital barometer, which is portable and more accurate than the traditional type. This device uses an electrical capacitor to measure air pressure.
Air Pressure and Weather
Areas with low pressure are generally associated with bad weather. If an area has low air pressure, air from neighboring areas, which have higher air pressure, will move in. This change, in turn, will cause the air to move upward, as it has nowhere else to go. When the air moves up, water vapor will condense, which will lead to the formation of clouds and rain.
Areas with high pressure, on the other hand, are typically associated with good weather. In high-pressure areas, low-level air will spread outward, allowing air above to come down. This downward motion warms the air up, causing evaporation and leading to nice, dry weather.
Air Pressure and Science Experiments
Here are 10 simple air pressure experiments for kids that can help them better understand its effects.
1. Indoor Tornado Experiment
This experiment will allow you to create a tornado in a bottle. You will need:
- A transparent mayonnaise jar
- Liquid dish soap
- Food coloring
To do the experiment, complete the steps below:
- Pour water into your jar until it’s roughly two-thirds full. Then, add several drops of food coloring to the water. Any color is fine.
- Add in one teaspoon of your liquid dish soap and one teaspoon of vinegar.
- Put the lid on the jar. Make sure it’s on as tight as possible to avoid leaks and serious messes.
- Shake the jar, then give it a twist so that the liquid inside will start spinning.
What you’ll observe is a small vortex that resembles a tornado.
2. Unspillable Water Experiment
In some situations, air pressure is stronger than gravity. This experiment demonstrates the strength of air pressure as it keeps the water in a glass in place — even when the glass is turned upside down.
This experiment requires:
- A juice glass
- An index card (4 x 6 inches)
The steps are as follows:
- Fill your glass with water right up to the top. Allow the water to run over so that the lip of the glass is wet.
- Put the index card over the full glass. Use your hand to press the card down firmly, making a good seal around the glass’s wet lip.
- While working over a sink or tub, hold your card in place with one hand and turn the glass over. Then, let go of the card carefully. It will not move, and the water will remain inside the glass.
This experiment demonstrates that the force the air pressure exerts against the index card is even stronger than the force gravity exerts on the water in the glass. The air pressure keeps the card from moving.
3. Book Blowing Experiment
The book blowing experiment demonstrates how powerful compressed air can be.
For this project, you’ll need:
- Three books
- A large plastic bag that’s airtight
To perform this experiment, follow these four steps:
- Stack three books on top of one another.
- Ask the student to move the books by blowing in their direction. Of course, they won’t be able to.
- Place the plastic bag on your table, then place the three books on top of it. The bag’s open end should hang out over the table’s edge.
- Show that if you blow with enough force, the books will start to rise off the table. It’s the compressed air in the bag that’s causing the movement.
4. Caved-In Can Experiment
This experiment involves using the power of air pressure to crush a can. You’ll need:
- A large container
- Ice cubes
- A measuring cup
- An empty soda can
- A stove
- Potholders or tongs
Once you’ve acquired the materials, follow the steps below:
- Fill the container with ice cubes and water. Set this container to the side so that you can use it later on.
- Pour 1/2 cup of water into your empty soda can.
- Put the can on a stove burner. If your student does this step, be sure to supervise them.
- When steam starts to come out of the hole at the top, you’ll know the water inside is beginning to boil. Turn the stove off, and use the potholders or tongs to take the can off the burner.
- Quickly place the can in the container with the ice water by turning it upside down and resting it on its top. Now you can observe the can collapsing as it cools down.
In this experiment, when the water was heated in the can, steam was produced, which pushed the air out of the can. Then, when the can was submerged in the ice water, the temperature of the steam lowered, causing it to condense back into water. This change, in turn, caused the air pressure inside the can to be much lower than the air pressure outside, and the weight of the air outside crushed the can.
5. Magic Egg Experiment
This experiment involves using the force of air pressure to push an egg through the neck of a bottle. Gather the following materials to perform this experiment:
- A hard-boiled egg
- A bottle with a neck wide enough that the hard-boiled egg can squeeze through
- A match
This experiment involves the following steps:
- Take the shell off your hard-boiled egg.
- Light the match and toss it into the bottle.
- Set the peeled egg on the bottle’s mouth, with the small end of the egg down. The egg will then pop into the bottle.
When the air in the bottle is consumed by the flame of the lit match, it causes the air pressure in the bottle to become lower than that outside of the bottle. The higher air pressure outside exerts a force on the egg, pushing it inside the bottle.
6. Plunger Experiment
This simple experiment only requires two clean, old-fashioned rubber-and-wood-stick plungers. To conduct the experiment:
- Stick the two plungers together. You might need to get the rims wet first.
- Try separating them.
Completing the separation is much harder than most kids imagine. When you rammed the two plungers together, you forced out the air from the cavity that the insides made when they were pushed together. This air being forced out caused the air pressure inside to be much lower than that outside. As higher air pressure always pushes, it kept the two plungers together.
7. Ping Pong Funnel Experiment
The ping pong funnel experiment involves having a ping pong ball in the bowl of a funnel and blowing through the funnel. The ball, instead of being blown away, is tightly held in the bowl. To complete the experiment, follow two steps:
- Insert the ping pong ball into the funnel and blow on it hard. Try tilting your head back so that the end with the ball is pointing toward the ceiling. See if you can blow hard enough so that, when you invert the funnel, the ball doesn’t blow away.
- See if you can pick the ball up from the table.
When you blow into the funnel, the air where the ball is moves more quickly and creates a lower air pressure than the rest of the air that surrounds the ball. As a result, the air pressure underneath the ball is lower than the surrounding air, which is a higher pressure. The higher pressure air pushes the ball back into the bowl of the funnel — regardless of which way you point the funnel.
8. Fountain Bottle Seal Experiment
The fountain bottle seal experiment demonstrates using air pressure to push water through a straw. Gather the following materials:
- A water bottle (2 liters)
- A lump of clay
- A long straw
Follow these three simple steps:
- Fill the water bottle halfway with water.
- Seal the bottle using the lump of clay wrapped around the straw so that the bottle’s mouth is completely sealed.
- Blow into the straw forcefully. You will notice that water begins to come out of the straw.
When you blow into the bottle, the air pressure inside the bottle increases, which in turn exerts a force on the water, forcing it up the straw.
9. The Million Dollar Bet Experiment
For this experiment, you’ll need:
- A water or soda bottle
- A piece of paper
To do the experiment, follow these steps:
- Lay the bottle down horizontally on a table.
- Wad up the ball of paper and stick it in the bottle’s mouth. The ball should be roughly half the size of the bottle’s opening.
- Challenge the student to blow the wad of paper into the bottle, saying “I bet you a million dollars you can’t blow the paper into the bottle!”
Those attempting the experiment will find it very difficult to get the paper to go in the bottle because there’s no place for the air that’s already inside to go except out through the bottle’s mouth, in which case it would take the paper with it.
10. Flying Papers Experiment
For the Flying Papers Experiment, all you need is a normal sheet of paper. Hold the sheet to your bottom lip, and then blow across the sheet. You’ll notice that the sheet flies upward! This same phenomenon explains how airplanes can fly. By blowing across the sheet, you’re lowering the air pressure, as the air is moving faster. Because the air pressure on the underside of the sheet is now relatively higher, it pushes the sheet of paper upward.
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