Weather Notes Part III (3)
Water in the atmosphere can be in all three states of matter (solid, liquid and gas)
Solid- snow, hail and sleet
Liquid – rain, mist, fog and clouds
Gas - Humidity
Water vapor- The gaseous state of water in the atmosphere
Condensation- Is the change of a gas to a liquid
Evaporation – Is the change of a liquid into a gas
Humidity – Water vapor in the air
Hot air – holds more moisture/humidity
Cold air - holds less moisture/humidity
Relative Humidity – is the amount of water vapor in the air compared to the amount of vapor
needed to saturate the air at its current temperature. It is reported in percent (%)
Dew point – The temperature at which condensation occurs. The dew point can vary depending
on the humidity in the air
Drop of water on your hand Lab:
During our activity we placed a drop of water on our hand and blew a light breeze across our
hand. The water droplet moved around our hand. After a few minutes the water droplet
evaporated into the air and became water vapor. Our hand felt cooler as this happened because
the evaporation of the water cooled our skin similar to the way our sweat cools our bodies on
hot summer days.
Sling Psychrometer (Wet bulb and dry bulb)
During this activity we used a sling psychrometer to measure the relative humidity in the
classroom. The psychrometer has two thermometers attached to it. One stays dry and the other
has a piece of fabric that get wet with water. We spun the thermometers for four minutes and
took the temperature of each when done. Then we took the reading of the dry thermometer and
the difference of the wet thermometer and used the data table to figure out the relative
humidity of the classroom. It was low 30-40%.
Cloud in a bottle:
During this activity we created conditions similar to what is needed in nature for a cloud to
form. We filled the bottle with air and place about 25 ml of water in the bottom. We shook the
bottle up and filled the air with as much humidity as we could. We placed a match in the bottle
to represent the pollution, dust and pollen in the air. We pump air into the bottle to raise the
temperature. Then we released the air quickly and a cloud formed because the water in the air
condensed on the smoke and dust particles that were in the bottle.
Observing Clouds
Stratus :
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Clouds that form low to the ground.
They form is stable air.
They are often large and Gray.
Total gray skies are stratus clouds
Cumulus:
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Puffy white clouds
Small and scattered
Usually means good weather and are referred to as fair-weather clouds
Cirrus:
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Clouds that are made from falling ice crystals
They from very high in the atmosphere
Look like long strands on pulled cotton candy. The longer they look the harder the wind
is blowing
Usually indicate air is dry and good weather should continue
The Water Cycle
Evaporation, Condensation and Precipitation
The sun evaporates water from lakes and oceans. As the air rises, it cools. The water vapor
condenses into tiny droplets of water. The droplets crowd together and form a cloud. Wind
blows the cloud towards the land. The tiny droplets join together and fall as precipitation to the
ground. The water soaks into the ground and collects in rivers and lakes. The cycle that never
ends has started again!
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#1 = The Sun
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#2 = Clouds
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#3 = Evaporation
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#4 = Precipitation
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#5 = The Ocean