Air Pressure?

Introduction: (Initial Observation)

Do you know why air planes can not go to the moon? Or why astronauts wear space suits? Or why it is hard to climb to Everest? Or what drives pneumatic equipment?

The answer to all these questions is air pressure.

When you learn about air pressure, you can stand in your back yard and calculate (estimate) the height of atmosphere.

You can fill up a cup with water and turn it upside down and show every one that water will magically stay in the bottle.

In this project we will investigate and demonstrate the power and benefits of air pressure.

Depending on the purpose of your science project, you may select one or more of the related experiments to perform.

Information Gathering:

Find out about air pressure. Read books, magazines or ask professionals who might know in order to learn about the effect and benefits of air pressure. Keep track of where you got your information from.

The following are samples of information that you may gather:

Air pressure is the force exerted on you by the weight of tiny particles of air (air molecules). Air molecules are invisible, however, they still have weight and take up space. Since there’s a lot of this empty space between air molecules, air can be compressed to fit in a smaller volume. When it’s compressed, air is said to be under high pressure. Air at sea level is what we’re used to, in fact, we’re so used to it that we forget we’re actually feeling air pressure all the time. Air pressure is measured with a barometer. Barometers are used to measure the current air pressure at a particular location in “inches of mercury” or in “millibars” (mb). A measurement of 29.92 inches of mercury is equivalent to 1013.25 millibars.

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

The purpose of this project is to demonstrate the uses and power of air pressure. We will do it by design or finding experiments that shows or benefits from air pressure.

As a part of this project I want to know how the temperature affects the volume or pressure of air in a container. This is tested in Experiment number 6.

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

The demonstration experiments do not need defining variables.

For the question of affecting temperature on air pressure, following is how you define variables:

Independent variable (also known as manipulated variable) is the air temperature.

Dependent variable (also known as responding variable) is the air pressure.

Constants are the amount of air and the volume of the container.

Hypothesis:

Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.

This is a sample hypothesis:

Air pressure will increase by any increase in the temperature.

My hypothesis is based on my gathered information that heat can cause expansion in solids, liquids and gases. By keeping the volume constant, additional pressure will build up.

Materials and Equipment:

List of materials can be extracted from experiments.

Experiment Design:

Experiment 1: (Egg in Bottle)

In this experiment we try to fit a hard-boiled egg into a container that has an opening that is a little small for the egg to fit into.

Material needed for this experiment are:

• • a hard boiled egg
  • a glass baby bottle or bottle with a neck that is just a little too small for the egg to fit through
  • a piece of paper
  • matches or lighter
  • some cooking oil, butter, or margarine

Warning: This experiment uses fire, so be careful and follow all safety procedures. Never do fire experiments when you are alone, even if you are an adult. If you are not an adult, then at least one of the people with you should be an adult. Think through the experiment before you try it, to be sure that everything you do is safe.

For this experiment, we are going to put a hard boiled egg into the bottle. First, you a need a hard boiled egg. Let it cool and carefully remove the shell. Be sure not to damage the egg, as this will cause the experiment to not work properly. If you accidentally tear your hard boiled egg, chop it up and put it on a salad. It makes a nice snack while you are boiling another egg.

After you peel the egg, you have to put it in the bottle. Put the oil, butter, or margarine around the inside of the mouth of the bottle and then gently place the egg on the top of the bottle. Not much happens. It just sits there. If you tried to push the egg into the bottle with your fingers, the egg would tear. We want the egg to be whole when it is inside the bottle. How are we going to do it?

We will start by removing the egg from the top of the bottle. CAREFULLY hold a piece of paper about one inch wide and three inches long. While you are holding one end, use the match to light the other end. As soon as it is burning, drop it into the bottle and quickly place the egg on top. Watch carefully what happens.

The paper burns for a second or two. As the fire goes out, the egg begins to move downwards into the bottle. It squeezes through the neck and drops into the bottle. How did that happen?

Most books will tell you that the paper burned up the oxygen, lowering the air pressure inside the bottle, and that the greater air pressure on the outside of the bottle pushed the egg inside. They are right about the air pressure part, but the lowered pressure in the bottle is not due to the burning of the oxygen.

When you burn paper in oxygen, the carbon in the paper combines with oxygen in the air to form a new gas called carbon dioxide. This gas takes up about as much space as the oxygen, therefore, the burnt oxygen is replaced with carbon dioxide and the pressure in the bottle stays the same.

But if the egg was pushed into the bottle by air pressure, what lowered the pressure in the bottle? The answer is temperature. While the paper was burning, it heated the air in the bottle. The heating air expanded and pushed out past the egg. If you put the egg on the bottle quickly and watch carefully, you may be able to see the egg shake as the air rushes out past it. As the flame begins to die down, the air inside the bottle cools. As it cools, it gets smaller, reducing the pressure in the bottle. The egg acts as a cork, sealing the top of the bottle to keep air from coming in to balance the pressure. Instead, the higher outside pressure pushes the egg into the bottle.

Now, how do we get the egg out of the bottle? One way is to turn the bottle upside down, with the egg resting in the neck of the bottle. Put your mouth against the mouth of the bottle and blow as hard as you can. This increases the pressure inside the bottle. Quickly move the bottle away from your mouth and the egg should pop out. Rinse off the carbon from the burned paper and now your egg is edible.

Experiment 2: (Make a barometer)

Materials

• Glass or aluminum, or hard plastic bottle.
• Plastic tube.
• Gum or glue.
• Water or colored water.

Instructions:
Bend a thin clear plastic tube to make a U shape with an attachment. Put some water in the U section of your tube. (Colored water is more visible). Secure your tube on the side of a cardboard. Insert the attachment tube into a glass bottle and use some glue or gum to make it air tight.

Your bottle can be mounted horizontally or can stand vertically.

What’s happening

High pressure will make the colored water go up on the bottle side and low pressure will make it go down on the bottle side. Movement of water in the opposite side of our U tube will be reverse.

Question:

What happens to your barometer when a big storm comes? Record your observations for about 2 weeks. Can you use your barometer to predict a storm?

Experiment 3:

The Magic Can – a demonstration of pressure

1. Take the coffee can and punch 3 small holes in the bottom. Also punch one hole in the plastic lid.
2. Now fill the can about 1/2 way with water and put the lid on.
3. Place your hand over the hole and press down on the lid. Notice how the water streams out of the holes on the bottom due to the pressure you are exerting on the lid.
4. Now slowly stop applying pressure to the lid. Notice how the stream of water stops. You can stop and start the flow of water simply by removing you finger from the hole. (Now would be a good time to hand the can to one of your parents…)

When you filled the can only half full, you left some space empty. This space actually was not empty – it was filled with air. Pressure on the lid exerted pressure on this air, which in turn exerted pressure on the water, forcing it out of the can. When you stop pressing on the lid, and leave your finger over the hole, the pressure of the air outside the can holds the water up from the bottom.

Experiment 4:

The Enchanted Cardboard

Can you imagine a column of water floating in mid air? We will actually accomplish this in this experiment.

You will need:

• • a plastic cup filled 3/4 full with water

• • a stiff sheet of cardboard or plastic

• • a sink to perform the experiment over (things can get a little wet in this experiment)

Wet down the rim of the cup and one side of the cardboard with water. Next, place the wet side of the cardboard on top of the rim of the glass. Then, very carefully turn the glass upside-down while keeping the cardboard firmly pressed against the rim of the glass with one hand. If you do it carefully enough, a small amount of water will pour out of the glass — that’s supposed to happen. But try not to let any air bubbles get into the glass. Finally, slowly remove the hand holding the cardboard in place.

What will happen?

Experiment 5:

Can Crush Experiment

In this experiment we create a condition that the pressure inside a can be less than the atmospheric air pressure. That will allow us to see the effect of atmospheric pressure.

Material needed: 1 gallon metal can, hot plate, heat resistant gloves and adult supervision.

Note that this experiment can be performed on any metal can.

Step 1:
A small amount of water (relative to the can) is added to the can. The cap is left off of the can and the can is placed on the hot plate. The can is left on the hot plate until the water begins to boil. After the water has started boiling, the can is left on the hot plate for some time.

During this step, the water is allowed to boil. Some of the water’s particles are changing from liquid state to gas state. These warm gas particles rise above the liquid. This steam slowly forces the air particles out of the can. Eventually, the can will contain almost entirely the liquid water at the bottom and water vapor in the rest of the can. Almost all of the air will have been forced out of the can.

The air outside the can is trying to press the can inwards with a certain amount of pressure. The water vapor inside the can, however, is trying to expand the can outwards with the same amount of pressure. Since these two pressures cancel, the can is unchanged. In order to maintain this equilibrium, the water vapor is escaping out the top of the can.

Step 2:
The can is quickly sealed using the original cap. It is very important that the cap is securely sealed. The can is then removed from the hot plate (in order to protect the table, it may be necessary to place the hot can on a piece of wood).

Step 3:
After some time, the can begins to slowly crush in on itself, often very loudly! (To speed the process along, ice is sometimes placed on top of the can.)

Immediately after the cap has been placed securely on the can and the can has been removed from the hot plate, the can contains almost entirely water and water vapor. As discussed above, the water vapor is trying to expand the can with the same amount of pressure that the air is trying to crush the can. As the can sits in room temperature, however, there is an exchange of thermal energy between the warm water vapor and the cool air (the can acts as an intermediary). This causes the water to cool. Eventually, the water cools so much that it begins to condense. Some of the water vapor particles are changing from gas state to liquid state. Since the pressure exerted by a liquid on the sides of its container is much less than the pressure exerted by a gas, the pressure inside the can begins to drop. This pressure drop causes the can to be crushed by the air surrounding the can.

Experiment 6: How does the temperature affect the air pressure in a closed container

Introduction:
Gas containers or cylinders are designed to resist certain pressures. Excessive pressure increase may cause the container to burst and explode the same way that a rubber balloon does. In this experiment we want to know how the air pressure in a closed container changes in different temperatures.

One possible way to do this experiment is by using a steel container and a pressure gage similar to those used to measure the pressure of air in automobile tires. Then we can simply modify the temperature with any heat source and measure and record the pressure. The problem is that not all students will have access to such equipment. To simplify the process we can measure the volume increase instead of pressure increase. We can then use the formula P1.V1=P2.V2 to calculate the pressure.

The above formula that can be found in physic books means that the product of pressure and volume for any amount of gas is constant. As you reduce the volume, the pressure will increase in a way that:

Initial pressure X Initial volume = Secondary pressure X Secondary volume

Materials:

• • Glass or hard plastic bottle.
  • clear plastic tube with known inside diameter
  • Gum or glue
  • water or colored water
  • ruler
  • Glass thermometer

Procedure:

Bend the clear plastic tube to make a U shape with an attachment (similar to what you did in experiment 2).

Put some water in the U section of your tube. (Colored water is more visible.)

Place the thermometer inside the bottle in a way that you can read the temperature.

Secure the tube on the side of a cardboard. Insert the attachment end of the tube into the bottle and use some glue or gum to make it air tight.

To the best of your ability, calculate the total volume of air in the bottle, including the attached air in the tube.

Place the bottle on ice to make it cold. Read the temperature and when it increases 5 degrees, mark the level of water in the tube.

Remove the ice so the bottle starts to warm up. On every 5 degrees temperature increase, record the temperature, place a new mark on the tube, measure the volume increase, and calculate the total new volume. Finally, record all your in your data table.

When the bottle temperature gets to the room temperature, you will need to use a hair dryer to warm up the bottle to higher temperatures. Do it slowly and continue to record the temperature and volume every 5 minutes or ever 5 degrees (Celsius or Fahrenheit).

Your results table may look like this:

Use the formula P1.V1=P2.V2 to calculate pressure change and record pressure changes in your results table.

Make a graph:

Use the temperature column and the pressure column of your results table to draw a line graph. If you don’t know how to make a graph, click on “How to start” in the control panel and find the link about making graphs.

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.

Summery of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

This experiment turned out the way we expected. The egg was forced into the jar due to the unbalance ness of pressure.

Conclusion:

Using the trends in your experimental data and your experimental observations, try to answer your original questions. Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

How much pressure is on our bodies?

Earth’s atmosphere is pressing against each square inch of you with a force of 1 kilogram per square centimeter (14.7 pounds per square inch). The force on 1,000 square centimeters (a little larger than a square foot) is about a ton!

Why doesn’t all that pressure squash us?

Remember that you have air inside your body too. That air balances out the pressure outside, so you stay nice and firm and not squishy.

Why do my ears pop sometimes when I go to higher elevations?

If you’ve ever been to the top of a tall mountain, you may have noticed that your ears pop and you need to breathe more often than when you’re at sea level. As the number of molecules of air around you decreases, the air pressure decreases. This causes your ears to pop in order to balance the pressure between the outside and inside of your ear. Since you are breathing fewer molecules of oxygen, you need to breathe faster to bring the few molecules there are into your lungs to make up for the deficit. As you climb higher, air temperature decreases. Typically, air temperatures decrease about 3.6° F per 1,000 feet of elevation

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.

References:

http://kids.earth.nasa.gov/archive/air_pressure/

http://www.tnrcc.state.tx.us/air/monops/lessons/airpressurelesson.html

http://www.iit.edu/~smile/ph9603.html

http://www.grc.nasa.gov/WWW/K-12/airplane/pressure.html

http://www.ed.uiuc.edu/YLP/Units/Curriculum_Units/95-96/Weather_GChung/own_barometer.html

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