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Cold air is Dense

Introduction:

we wish to set up a learning case in which students will discover, with the examination and manipulation of real data from a herbal environment, that:air has mass and density, andcold air is denser than warmth air. These insights space absolutely an essential to knowledge virtually everything around weather and climate. Until a student has actually his or she mind firmly roughly these two concepts, the or she is not all set to understand exactly how storms work, not prepared to know why the prevailing winds blow the method they do, not prepared to understand why deserts take place where lock do.Although these two principles are an essential underpinnings of basically every physical procedure in the atmosphere, they space not intuition obvious--in fact, they room counter-intuitive. The student looks about at the wait skeptically-- if there are so numerous molecules in that air, why can"t we see them? If air has weight, why doesn"t it register on a scale? On hot summer nights, the air feels oppressive, heavy--don"t phone call me that hot August wait is low density "Air has mass", "air has actually density", and also "cold air is dense" space the kinds of statements that students often tend to memorize and also parrot back, there is no actually altering their world-view, because these declaration don"t fit through their day-to-day endure of real-life air. Because an understanding of the relationship between density and temperature of air is basic to so many natural processes, however is counter-intuitive, it is a good investment of student and also instructor time to construct this understanding upwards from a solid communication in the monitoring of genuine data.

Insights/Curriculum Highlights:

Air is do of molecules, and therefore has mass. Barometric pressure is a measure up of how much mass of air, i.e. How many air molecules, exist above the point of measurement, all the method up to the peak of the atmosphere. Therefore, barometric pressure decreases through elevation. Any given volume the air has actually density. The thickness of air deserve to vary from place to place and also from time come time.The distinction in barometric pressure in between observation web page at various elevations is a measure of the thickness of air in a tower of air in between those two elevations.Cold wait is denser than warm air.

Thinking skills / Pedagogical Highlights:

Making a connection between laboratory range observations and also atmosphere-scale data sets. Drawing on hand-operated observations to define an facet of a organic system. Thinking around a phenomenon (density that air) that is invisible. Imagining limits or limits, and thinking about phenomena in ~ those boundaries (a shaft of air, a package of air)Linking nature that space detectable to the human being senses (e.g. Wait temperature) with molecular scale phenomena (molecules per volume that air).Linking nature that are measurable at the macroscopic scale (e.g. Barometric pressure) to molecular range phenomena (number of molecules). Structure a chain of thinking from cause to effect.Building a chain of reasoning from observation to interpretation. Using time series graphs; comparing how different parameters vary with time. Recognizing the a measurable home varies with time (barometric pressure rises and falls together weather solution pass) and likewise through space (barometric pressure decreases with boosting elevation).Recognizing covariance: 2 properties varying in the very same direction under the affect of the exact same circumstances (barometric push at the open up Lowland website covaries v that at the Ridgetop site). Using a scatterplot; thinking about two or 3 data parameters simultaneously.

Procedure:

1. Introductory hand-operated Investigation: do a BarometerStudents develop home made barometers and also discuss how they work. Instructions for this activity are included in numerous middle institution science books. See, because that example: R. L. Bonnet and G. D. Keen, earth Science: 49 science Fair Projects, TAB Books, 1990, pp. 127-131.2. Video : Torricelli"s exploration of wait pressureStudents view and discuss the ar of the "Connections" video in i m sorry Torricelli"s discovery of air pressure is illustrated. In this video, a mercury barometer is carried up a mountainside, and also the mercury is checked out to fall as the climber ascends. (Alternatively, students have the right to read a description of the same discovery in the publication Connections through James Burke, 1978, Little, Brown & Co, Boston, pp. 74-17.) The translate is that the weight of the mercury balances the load of the overlying air. The load of the overlying waiting decreases together the climber rises greater in the atmosphere; thus less load of mercury is required to balance the reduced weight of the overlying air. 3: reproduce Torricelli"s experiment in a tall buildingUsing a handheld barometer, students will certainly measure the barometric push at street level. Then, emulating the experimenter in the "Connections" video, they will certainly climb the stair or ascend the elevator of a high building, measure barometric pressure at every landing or at several stops follow me the way. They observe the the air pressure at the street level is higher than in ~ rooftop level (figure 1). Because that a twelve story building the difference in air push is about 4 mb. The structure needs to it is in at the very least 8 stories high to register an unambiguous barometric push difference. 4. Data-based investigation: barometric pressure from BRF Students study barometric press data sets that were videotaped at open Lowland and also Ridgetop sensor web page at black color Rock Forest. (figure 2). Display should it is in zoomed so the a month of two at a time is visible. Every pair the students have the right to be responsible for several months that data. Data can be published out and also scotch videotaped together to form a long time series of a year or much more duration. (If printouts from various students room combined, be certain that every students collection the plot vertical scale the same.) Points come observe:Over time, the barometric pressure at each website goes up and down, up and also down. The periodicity is about a week, however the sample is not really regular.Barometric push at the Ridgetop website is constantly less 보다 at the open Lowland site. Barometric press at Ridgetop and at open Lowland covary: in other words, once one walk up, the various other goes up; as soon as one walk down, the various other goes down. The difference between the barometric push at Ridgetop and also Open Lowland is bigger than the difference between the high and also low pressures at one of two people Ridgetop or open Lowland. In other words, the variability in an are is greater than the variability gradually in this data set. Point out to figure out and/or discuss: The up and also down wiggles of each barometric push record reflect weather solution passing throughout the field area. (This can be the subject of a separate investigation, in which students find the relationship between barometer trends and also sunny or merganser weather.) Barometric pressures at the 2 sites covary since they room subject to the same weather systems.Which site carry out you think is at higher elevation? Think around the hand-operated experiment with the hand-held barometer, and around the experimenter in the connections video. The Ridgetop Site need to be at greater elevation than the open up Lowland Site because it constantly has a reduced barometric pressure. Ridgetop has actually a reduced barometric pressure than open Lowland due to the fact that fewer molecule of air lie in between the Ridgetop site and also the top of the atmosphere than lie between the open up Lowland site and the peak of the atmosphere. We usually think around barometric pressure variation in the paper definition of changes through time ("the barometer is falling" or "the barometer is rising"), related to the i of weather systems. Quantitatively, however, the spatial sports of barometric pressure with key is bigger than the temporal sports at any kind of given site. (Optional) making use of your outcomes from the hands-on examination with the barometer and also the high building, plus your observations of barometric push at black color Rock Forest, calculation the distinction in elevation in between the Ridgetop Site and the open up Lowland Site.5. Data-based investigation: qualitative relationship in between density & temperature that air return to the lengthy time series of barometric push versus time end the course of the year, students will certainly observe that the push difference in between the ridgetop and lowland is not constantly exactly the same. The difference in pressure between the 2 sites is a measure up of the mass or thickness of the pillar of waiting in in between the reduced and higher elevations. What is an altering the thickness of the pillar of air in between the ridgetop and lowland elevations? Students study digital photographs tape-recorded at the exact same time and place each week. Each student or college student pair is responsible for someday of data, v data to adjust spaced one or two weeks personal (the entire course should span fifty percent a year of data). For their day, each student-pair assembles a sheet of paper with the digital photograph, add to a number representing the difference in between the barometric push recorded in ~ the ridgetop and also the lowland train station on their day (figure 3). The sheets of file will then be arranged follow me a wall surface in order from shortest to highest number; i.e. In order native least thick to most dense column the air between ridgetop and also lowland elevations. The students will then examine the photographs, in search of patterns or trends. Us anticipate that the students will observe the the snowy cold-looking photographs are clustered in ~ the high air-density end of the continuum, and also the summery hot- feather photographs are clustered at the low air-density end of the continuous (figure 3). Students shot to describe the relationship between the time that year and also the density of the tower of air. Teacher guides conversation with examples of materials that become less thick as they gain warmer, for instance mercury in a barometer. Course eventually hypothesizes the a cold pillar of wait is an ext dense than a heat column of waiting (figure 4). 6. Data-based investigation: quantitative relationship between density & temperature of wait (for solid high school students or undergraduates) Students check the hypothesis (figure 4) the cold waiting is denser than heat air, and that this is why the difference in barometric pressure in between the Ridgetop and also Open Lowland website is bigger is cold weather. They do a graph reflecting the air temperature together the live independence variable, and the difference between barometric press at open up Lowland and Ridgetop as the independent variable. (figure 5). The difference in barometric pressure between the open Lowland site and also the Ridgetop website is a measure of the mass or density of the shaft of air in between the 2 elevations. Students watch a strong correlation between temperature and barometric pressure distinction (figure 5). This supports the hypothesis that air temperature is affecting the weight (density) that the shaft of air in between the ridgetop and also lowland elevations.


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Teacher can comment on this observation in terms of the habits of gas molecules in an answer to heating or cooling. Created by Kim Kastens, Lamont-Doherty earth Observatory (kastens