The Ridgetop Site must be at higher elevation than the Open Lowland Site because it always has a lower barometric pressure. Ridgetop has a lower barometric pressure than Open Lowland because fewer molecules of air lie between the Ridgetop site and the top of the atmosphere than lie between the Open Lowland site and the top of the atmosphere. Quantitatively, however, the spatial variation of barometric pressure with elevation is larger than the temporal variation at any given site. Using your results from the hands-on investigation with the barometer and the tall building, plus your observations of barometric pressure at Black Rock Forest, estimate the difference in elevation between the Ridgetop Site and the Open Lowland Site. The difference in pressure between the two sites is a measure of the mass or density of the column of air in between the lower and higher elevations.
Students examine digital photographs recorded at the same time and place each week.
The students will then examine the photographs, looking for patterns or trends. Students try to explain the relationship between the time of year and the density of the column of air. Teacher guides discussion with examples of materials that become less dense as they get warmer, for example mercury in a barometer. They make a graph showing the air temperature as the independent variable, and the difference between barometric pressure at Open Lowland and Ridgetop as the independent variable. The difference in barometric pressure between the Open Lowland site and the Ridgetop site is a measure of the mass or density of the column of air between the two elevations.