Air Pressure Pressure in the real world

Transcription

1 Air Pressure Pressure in the real world OBJECTIVES Students will conduct experiments and collect data. Students will learn how air pressure affects real-world phenomena. Students will gain an understanding of air pressure. MATERIALS Experiment #1 straws paper cups Kool Aid 125 ml Erlenmeyer flask cork or rubber stopper CORE LEARNING GOALS The student will apply addition, subtraction, multiplication and/or division of algebraic expressions to mathematical and real-world problems The student will apply formulas and/or use matrices (arrays of numbers) to solve real-world problems The student will make informed decisions and predictions based upon the results of simulations and data from research. CALCULATOR SKILLS Simple calculations using order of operations. EQUATIONS Area (rectangle) = length x width Area (circle) = π x r 2 Experiment #2 mason jar index card water Experiment #3 wooden ruler notebook paper newspaper Experiment #4 large mouth jar (such as a large institutional pickle jar) plastic sandwich bag tape Experiment #5 2 rubber plungers (one with a small hole drilled into it)

2 Experiment #6 1 one gallon plastic milk jug 2 one gallon glass jugs water 3 one-holed rubber stoppers glass tubing rubber tubing Experiment #7 2 Coke cans hot plate pan of ice water tongs Challenge #1 straws tape scissors ACTIVITIES 1. Hands On Activities Experiment #1 Experiment #2 Experiment #3 Experiment #4 Experiment #5 Experiment #6 Experiment #7 Challenge #1 2. Discussion ADDITIONAL RESOURCES

3 Air Pressure Pressure in the real world TEACHER GUIDE Lesson/Background: Air pressure is the force exerted on you by the weight of tiny particles of air (air molecules). Although air molecules are invisible, they still have weight and take up space. Since there s a lot of 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 are accustomed to, in fact, we re so used to it that we forget we re actually feeling air pressure all the time! Weather forecasters measure air pressure with a barometer. Barometers are used to measure the current air pressure at a particular location in inches of mercury (mm Hg) or in millibars (mb). A measurement of inches of mercury is equivalent to millibars. Hands On: Experiment #1 Every kid knows how to make a straw work, but why does it work? For this experiment have the following set ups: 1. A straw resting in a paper cup of Kool Aid or punch. 2. A straw with a couple of pinholes punched in halfway up the straw resting in a paper cup of Kool Aid or punch. 3. A straw inserted through a cork or one-holed rubber stopper into a 125 ml Erlenmeyer flask containing Kool Aid or punch. 4. Two straws and a cup of Kool Aid or punch with a card having instructions to put both straws into your mouth, to place only one of the straws into the liquid and to suck simultaneously on both straws. Ask the students to relate what happened or didn t happen in each instance and explain the observations. What did they do with their mouth and jaw as they sucked? Experiment #2 Fill a jar to the top with water and wet the rim slightly. Lay an index card on the top of the jar. Hold the card firmly in place and turn the jar over. Now take away your hand and see what happens. The water should stay in the glass, showing that air pressure is exerted on the card from the top, side, and the bottom.

4 This experiment is demonstrated in the movie: airpressureexp2.mpg Experiment #3 Lay a ruler on the table so that about 1/3 of it lies over the edge. Place two sheets of notebook paper on the ruler and press against the table until the paper is flat as possible. Now hit the overhanging portion of the ruler with your hand and try to make the paper fly into the air. Repeat this procedure using two sheets of unfolded newspaper and record the results. The ruler should snap when placed under the newspaper, but not when placed under the notebook paper. The notebook paper is small enough that the ruler can lift it without breaking, while the newspaper has a much greater surface area than the notebook paper. The air presses down on the sheet of newspaper, so there is a lot of air pushing down on it and this is enough to stop the paper and ruler from moving. This experiment is demonstrated in the movie: airpressureexp3.mpg Draw a square centimeter on the floor or put a single sugar cube on the floor. The column of air above the square centimeter weighs 1030g. Determine how many square centimeters of the ruler were covered with the newspaper. What is the weight of air pushing down on the ruler? If 65 cm x 3 cm is covered with the newspaper, the weight of air pushing down on the stick is g or kg, or 442 pounds. Experiment #4 Obtain a large mouth jar (a large institutional pickle jar from the cafeteria works well). Get a large plastic sandwich bag and invert over the mouth of the jar. Push it into the jar and smooth it out so that it clings to the inside surface. Securely tape the bag to the mouth of the jar. Challenge the students to reach into the jar and pull the bag out. They will not be able to do this unless they rip the bag. Why? Point out that there is no glue or other type of adhesive holding the bag to the jar. It is clear why the sandwich bag cannot be pulled out of the jar. If the bottom of the jar is 25 cm, then the area is π r 2 = 3.14 (12.5cm) 2 = 491cm 2. Now the weight of the air pushing down on the bottom of the jar is

5 491 cm x 1030 g/cm 2 = g, or kg or 1114 lb of air. This experiment is demonstrated in the movie: airpressureexp4.mpg Experiment #5 Have two students come up and get two rubber plungers, and push them against each other. Ask them to now pull them apart. They will come apart very easily. Have the students reattach the plungers, and hold them together making sure that the hole is covered with your thumb. It works even better if your thumb is wet. Now when students pull on the plungers they will stick together. Because there was a hole in one of them, air was allowed to come into the gap, meaning that the pressure on the inside and outside was the same. The pushing together of the plungers forced out the air and by plugging the hole, air was prevented from coming in and equalizing. Now when the plungers are pulled apart the volume of air trapped inside increases, lowering the pressure. Because all of the outside air pressure pushing on the outside of the plungers is many times greater than the small pressure on the inside, the plungers are not easily separated. The total force can be calculated from the total surface area of the two circles multiplied by 1030 g. If the plungers have a 10 cm diameter there is about g, or 150 kg, or 330 lb of pressure holding them together. This experiment is demonstrated in the movie: airpressureexp5.mpg Experiment #6 Prepare three jugs of water: 1 one gallon plastic milk jug, and 2 one gallon glass jugs. Fill the plastic one and one of the glass jugs with water. To the other glass jug, add water to the halfway mark. Prepare identical one holed rubber stoppers for each jug. Insert one end of a short piece of glass tubing into the stopper and attach some rubber tubing to the other end. Run water through the tubing to remove all air and pinch off the end of the tubing with your fingers so that water doesn t fall out the end with the rubber stopper. Insert the stoppers into the three jugs still pinching the rubber hose. Ask the students to predict from which jug the water will drain out the fastest. Elevate the jugs over the sink and stop pinching the tubing. Ask the class why the water drained out of the plastic jug but not out of either of the glass jugs.

6 The atmospheric pressure is pressing on all sides of the jugs equally. In the plastic jug the pushing of the air on the outside of the jug in addition to the weight of the water in the jug overcomes the pushing in of the air experienced at the mouth of the jug. Consequently the water can drain out. Only because the plastic collapsed in response to the air pressure can we have enough downward force to overcome the upward force and have water flow. The glass jug does not allow the outside air pressure to be transmitted to the water. The upward air pressure is greater than the downward weight of the water and no draining from the full jug takes place. A small amount of water may drain from the half filled glass jug. Turning the jug upside down forces a little of the water in the tube to drain out. Because no air entered, as some water drained out of the flask it lowered the pressure above the water in the jug low enough that after a few seconds the upward air pressure is greater than the combined air pressure and water pressure in the jug, and the draining ceases. Experiment #7 Heat two Coke cans on a hot plate. Use tongs to pick up the can and rapidly turn it upside down and throw in into a pan of ice water. Instantly it will be crushed. Repeat using a Diet Coke can. This time there will only be a slight implosion of the can. The trick: In the classic Coke cans, add a few ml of water, so that the heating fills the can with gaseous water. In the Diet Coke can, only hot air fills the can. Upon rapid cooling the gaseous water changes to liquid water (the volume changed by a factor of 70) reducing the pressure inside the can drastically. The air pressure pushing in on the can and down on the water in the pan immediately crushed the can and forced water inside. In the Diet Coke can the cold water merely cooled the hot air down with very little decrease in volume. This experiment is demonstrated in the movie: airpressureexp7.mpg Challenge #1 Ask students to predict the tallest straw that they could build that would allow them to drink a soda. Indicate that they can join two, three, or more straws together to make a super straw. (A short slit in one straw will allow the joining. A tight strip of tape to prevent leakage is recommended.) Have teams work on this problem.

7 The maximum height that they will be able to draw the liquid up is about 33 feet. This is equivalent to a pressure of 760 mm of mercury. In other words, the outside air pressure can only push up water to a height of about 33 feet, no matter how hard they suck. Because Coke has all the sugar in it and its density is greater than pure water, thy may not even be able to get it to rise 33 feet. After this activity it should be obvious why we use mercury instead of water. This challenge is demonstrated in the movie: airpressurechall1.mpg Discussion: 1. If you were on a mountain, would the weight of the air above you (air pressure) be greater than or less than it is now? 2. What do you think causes wind? 3. If you lived in Kansas and observed a sudden drop in air pressure, what kind of weather would you expect to see soon? 4. Why do hot air balloons rise? 5. Air weighs less than water, would you expect the pressure exerted by water to be greater or less than the pressure exerted by the same amount of air? Additional Resources: An engineering degree can take you anywhere that you want to go! The engineering resources section of the American Society for Engineering Education website offers information on engineering careers. ASME Pre-College education services include workshops, teaching materials and partnership opportunities to help teachers and engineers to strengthen the math, science, engineering, and technology skills of young people and to assist them in becoming more aware of the role of engineering in their lives.

8 The American Institute of Aeronautics and Astronautics realizes that learning starts with a teacher, a curious student, and fun in the classroom. Learn about how things work from helicopters to computers and more. Fun with algebra. Get help with your algebra homework online. NASA Connect the show that connects you to math, science, technology, and NASA. Turn imagination into reality with a future in engineering. Learn about the new faces of engineering as we recognize the new generation of engineers who are turning ideas into reality.

9 Air Pressure Pressure in the real world Student Worksheet Experiment #1 Everyone knows how to make a straw work, but why does it work? For this experiment have the following set ups: 1. A straw resting in a paper cup of Kool Aid or punch. 2. A straw with a couple of pin holes punched in halfway up the straw resting in a paper cup of Kool Aid or punch. 3. A straw inserted through a cork or one-holed rubber stopper into a 125 ml Erlenmeyer flask containing Kool Aid or punch. 4. Two straws and a cup of Kool Aid or punch. For this set up, put both straws into your mouth, place only one of the straws into the liquid and suck simultaneously on both straws. Relate what happened or didn t happen in each instance and explain the observations. What did you do with your mouth and jaw as you sucked? Experiment #2 Fill a jar to the top with water and wet the rim slightly. Lay an index card on the top of the jar. Hold the card firmly in place and turn the jar over. Now take away your hand and see what happens. Experiment #3 Lay a ruler on the table so that about 1/3 of it lies over the edge. Place two sheets of notebook paper on the ruler and press against the table until the paper is flat as possible. Now hit the overhanging portion of the ruler with your hand and try to make the paper fly into the air. Repeat this procedure using two sheets of unfolded newspaper and record the results. Draw a square centimeter on the floor or put a single sugar cube on the floor. The column of air above the square centimeter weighs 1030g. Determine how many square centimeters of the ruler were covered with the newspaper. What is the weight of air pushing down on the ruler? Experiment #4 Obtain a large mouth jar (a large institutional pickle jar from the cafeteria works well). Get a large plastic sandwich bag and invert it over the mouth of the jar. Push it into the jar and smooth it out so that it clings to the inside surface. Securely tape the bag to the mouth of the jar. Try to reach into the jar and pull the bag out. Even though there is no

10 glue or other type of adhesive holding the bag to the jar, you will not be able to do this unless you rip the bag. Why? Experiment #5 Have two students come up and get two rubber plungers, and push them against each other. Ask them to pull them apart. They will come apart very easily. Have the students reattach the plungers, and hold them together making sure that the hole is covered with your thumb. Now when students pull on the plungers they will stick together. Experiment #6 Prepare three jugs of water: 1 one gallon plastic milk jug, and 2 one gallon glass jugs. Fill the plastic one and one of the glass jugs with water. To the other glass jug, add water to the halfway mark. Prepare identical one holed rubber stoppers for each jug. Insert one end of a short piece of glass tubing into the stopper and attach some rubber tubing to the other end. Run water through the tubing to remove all air and pinch off the end of the tubing with your fingers so that water doesn t fall out the end with the rubber stopper. Insert the stoppers into the three jugs still pinching the rubber hose. Ask the students to predict from which jug the water will drain out the fastest. Elevate the jugs over the sink and stop pinching the tubing. Ask the class why the water drained out of the plastic jug but not out of either of the glass jugs. Experiment #7 Heat two Coke cans on a hot plate. Use tongs to pick up the can and rapidly turn it upside down and throw it into a pan of ice water. Instantly it will be crushed. Repeat using a Diet Coke can. This time there will only be a slight implosion of the can. Challenge #1 Ask students to predict the tallest straw that they could build that would allow them to drink a soda. Indicate that they can join two, three, or more straws together to make a super straw. (A short slit in one straw will allow the joining. A tight strip of tape to prevent leakage is recommended.) Have teams work on this problem. Discussion Questions 1. If you were on a mountain, would the weight of the air above you (air pressure) be greater than or less than it is now? 2. What do you think causes wind? 3. If you lived in Kansas and observed a sudden drop in air pressure, what kind of weather would you expect to see soon?

11 4. Why do hot air balloons rise? 5. Air weighs less than water, would you expect the pressure exerted by water to be greater or less than the pressure exerted by the same amount of air? Vocabulary: Pressure The force of the air as it pushes on a surface. It is measured either in pascals or in pounds per square inch. Additional Resources: An engineering degree can take you anywhere that you want to go! The engineering resources section of the American Society for Engineering Education website offers information on engineering careers. ASME Pre-College education services include workshops, teaching materials and partnership opportunities to help teachers and engineers to strengthen the math, science, engineering, and technology skills of young people and to assist them in becoming more aware of the role of engineering in their lives. The American Institute of Aeronautics and Astronautics realizes that learning starts with a teacher, a curious student, and fun in the classroom. Learn about how things work from helicopters to computers and more. Fun with algebra. Get help with your algebra homework online. NASA Connect the show that connects you to math, science, technology, and NASA. Turn imagination into reality with a future in engineering. Learn about the new faces of engineering as we recognize the new generation of engineers who are turning ideas into reality.