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Observing Air Stratification

Introduction

This experiment works best in a room with a very high ceiling. It also works best when there is a mixture of warm and cold air in the room. This might occur late in the day during the summer, when there is still hot air in the room but the air conditioner has been just turned on to cool the air inside the room.

Objective
To observe air stratification in our daily lives.

Equipment
Clamps and stand
Datalogger interface connected to a PC
2 temperature sensors
Metre stick
BluTack/tape

Experiment Setup

Set one of the external temperature sensors hanging down 3-5cm above the floor. Don't let it touch the floor, because the floor itself might be warmer or cooler than the air right near the floor. Use BluTack to hold it in place against the table, but make sure it does not touch the wall either. There should be air all around the sensor.

Place the other temperature sensor about 2 metres from the floor, but don't put it right above the computer monitor. The monitor gives off heat, and this will affect the sensor readings. Use a bit of BluTack to hold the sensor.



Connect the 2 temperature sensors to the datalogger interface. Place the interface in the middle of the 2 sensors. Use the datalogger software to plot the temperature collected from the 2 sensors in the same graph against time.


Results and Answers
At first the two lines will be very close together. Give the sensor a few minutes to register their new temperatures. Now look at the graph. Does the 2 lines show different temperatures? If so, why do you think this is? And if not, why do you think this is?


Conclusion
"Air stratification" is the result of hot air rising and cold air sinking. If you see a large difference, then you can see where all of your heat has gone! It is up near the ceiling, because warm air is less dense and more buoyant than cold air, causing it to rise. Cold air is denser and less buoyant, so it settles down near the floor. What if you do not see a difference? It could be that your ceiling is relatively low, so there is not enough room for the air to stratify (split into warm and cold areas). It could also be because all of the air in the room is the same temperature. Since it is the difference in temperature that causes stratification to occur, air that is the same temperature does not stratify. Also, if there is noticeable air movement (like a draught or a fan) in the room, the air will be mixed together and there will be less stratification.

 
  Heat
  Observing Air Stratification
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