This experiment illustrates the effect of pressure change and aerosols on cloud formation.
Materials:
1) Two clear, empty, plastic water bottles with lids. Remove labels.
2) Matches.
Directions:
· For the first bottle, add about 1 inch of hot tap water and put the lid on. Shake vigorously.
· Look through the bottle. It is best viewed in good lighting against a dark background.
· Squeeze the bottle as hard as you can, then release it. Repeat this 5 or 6 times.
· You are trying to see if there is any change in the air inside the bottle. To get a clear view, swirl the water around to remove condensation from the inside walls of the bottle.
· For the second bottle, again add about 1 inch of hot tap water, put the lid on, and shake.
· Take the lid off, light a match, blow it out, drop it into the bottle while it is still smoking, then immediately put the lid back on the bottle.
· Again look through the bottle, squeeze the bottle as hard as you can, then release it. Repeat this several times. Swirl the water as needed to remove condensation from the inside walls of the bottle.
· Safety precautions are always important “in the lab”. Take a moment to put the matches away, out of reach of children. Thanks!
Which bottle had better cloud formation, the one with smoke in it, or the one without?
Did the cloud appear when you caused high pressure on the air in the bottle (by squeezing), or when you caused low pressure (by releasing)?
What is happening?
The warm moist air in the bottle is close to saturation. Squeezing the bottle increases the air pressure which also causes an adiabatic temperature increase. This increased temperature allows more water to evaporate. Releasing the bottle decreases the pressure and temperature slightly and causes the excess water vapor to condense. The smoke particles are condensation nuclei which improve cloud formation.
The formation of the cloud when the pressure decreases is analagous to what happens to a parcel of air rising in the atmosphere.
Answer the following questions, based on the experiment and these sections in your textbook: Dew-Point Temperature, page 495
Adiabatic Temperature Changes, page 498
Condensation and Cloud Formation, page 596
The amount of vapor needed for saturation ________ with increasing temperature.
increases
decreases
Saturation occurs if sufficient water vapor is added to air, or if air is cooled to its dew point.
True
False
Cooling below the ________ causes water vapor to condense.
Air that is allowed to expand ________; air that is compressed ________.
cools; warms
warms; cools
When a parcel of air moves upward, it expands and cools.
True
False
In order for a cloud to form, air must be cooled below its _____ point.
In the experiment, squeezing the bottle causes pressure and temperature to ________; releasing the bottle causes pressure and temperature to _________.
increase; decrease
decrease; increase
Tiny bits of particulate matter known as ________ serve as surfaces for water vapor condensation.
Give two examples of condensation nuclei.
Explain why the cloud appeared when you released the bottle.
