# Temp and pressure relationship with altitude

### Barometric formula - Wikipedia In the atmosphere, as we increase altitude the pressure decreases which will decrease the density. As you say, the temperature also decreases. Aircraft Performance in Relation to Atmospheric Pressure, Density and at high altitudes is evidence of low temperatures at high altitudes. Air temperature is colder on top of a mountain than at sea level, but if heat rises the relationship between temperature and pressure: When you pressurize air (or It is this lower pressure at higher altitudes that causes the temperature to be.

Near sea level there are about 2. Air molecules are held near the earth by gravity. In other words, air has weight. Weigh an empty bag, then fill it with air, it now weighs more. In addition gases, like air, are easily compressed, i. In other words, we say gases are compressible because they can easily be squeezed into a smaller volume.

Solids and liquids on the other hand are not easily compressed. The weight of all of the air above a given point in the atmosphere squeezes air molecules closer together, which causes their numbers in a given volume to increase increase in number density. The more air above a level and hence the more weight of air above a levelthe greater the squeezing effect or compression. Since air density is the number of air molecules in a given space volumeair density is typically greatest at the surface or sea level where it is squeezed by the weight of the entire atmosphere above and decreases as we move up in the atmosphere because the weight of air above becomes less and hence there is less of a squeezing effect See Figure Z.

Pressure Atmospheric air pressure results from the Earth's gravitational pull on the overlying air. Without gravity holding the atmosphere just above the ground surface, air molecules would spread out, and the gas pressure would be close to zero. The weight of the atmosphere acts as a force upon the underlying surface of the Earth. The amount of force excerted over an area of surface is called atmospheric pressure or air pressure.

Near sea level, the average air pressure is about In this class we will use the unit millibars mb to specify air pressure. At sea level the average air pressure is mb. Another way to think of this is that the total weight of all the air above sea levels weighs enough to cause mb of air pressure.

Since the air a gas is a fluid, the pressure force acts in all directions, not just downward. The pressure force pushing downward due to the weight of the air is the same as the pressure force acting sideways and even upward.

### Lesson C3: Elevation and Temperature

If you are having trouble understanding this, make an analogy with another fluid liquid water. Consider a deep swimming pool full of water. The water pressure anywhere in the pool depends on the weight of the water above that is the deeper you dive downward in the pool, the stronger the water pressure. Measuring Air Pressure Barometric pressure is measured in millibars mb but is often given in inches because older style of barometers measured the height of a column of mercury to indicate air pressure.

Normal air pressure at sea level is An aneroid barometer measures air pressure by the expansion or contraction of springs, housed in a partial vacuum, in response to changes in air pressure. In older mercury barometers, a column of mercury would rise or fall in response to changes in air pressure.

Air pressure is constantly changing due to fluctuations in temperature, which is related to air density.

## Change in the Atmosphere with Altitude

Warm Temperatures Warm air causes air pressure to rise. When air molecules collide, they exert force on each other. When gas molecules are heated, the molecules move more quickly, and the increased velocity causes more collisions. This is very important because students should learn that the only way to confirm the influence that elevation has on temperature is to keep all of the other variables constant.

Therefore, any differences in the temperature patterns can be attributed to elevation since it is the only difference in the locations. After locating the cities, ask the students if they can make any predictions about the weather for any of the locations. You can organize the students in pairs or small groups so they can share and discuss their predictions with each other, however each student should be held responsible for answering each question.

This can be play an important part in assisting the students elaborate their thoughts. Since these are real time weather readings, the weather stations for each of the locations may submit the current temperatures to the weather web site at different times during the day, and therefore you should only compare the high temperature readings for today's forecast.

Analyze the Data The effect that elevation has on temperature can be analyzed by using a scatter plot to graph the two measurements. Scatter plots demonstrate a trend in the data and are similar to line graphs in that they begin by plotting different data points. However, the difference is that each of the individual points are not connected together with a line but rather a trend line is added where approximately the same number of points occur below the line as above it. The students can either use a spreadsheet program recommended or create a graph to manually plot the points. It is recommended that you do not use the same elevation temperature data and you should mention that a trend line will not cross every point and that they should not connect the dots but rather estimate where the line should fall so that approximately the same number of points below the line as above it.

When explaining what a trend line is, it will be helpful to mention that when most of the data points are on or close to the trend line, this generally means there is a close relationship between the data points. On the other hand, if the data is all over the graph and it is difficult to draw the trend line, this most likely means that there is little correlation between the two variables.

Students should be able to determine the approximate change in temperature for every increase of 1,m in elevation based on the graph. The correlation coefficient corresponds to how much the different data points are correlate.