To demonstrate the concept of evaporation
Plates - styrofoam or plastic, not paper (enough for partners)
one purple, orange, black crayon for each group
Humidity Detector - optional
Teacher wipes a damp sponge across the chalkboard. The class should watch
and make observations about what happens. They should notice the streak
slowly disappear. Ask:"Where does the water on the board go? What happens
to puddles after it rains? Where does the water go? Have you ever seen
clothes hung out on a line to dry in the sun and wind? Where does the water
from the wet clothes go?"
Do this lesson on a dry day, not a rainy or a foggy day. Divide the class
into partners. Each pair needs a plate and three different colored crayons.
Each pair should make a shallow puddle of water on their plate. Then they
should use a purple crayon to make a circle around their puddle of water.
Have each pair choose different places in the room to place their plate
(i.e. in the sun, in the shade, near a heat register, etc.). Let the plates
sit for about an hour. During that time make some predictions about what
will happen to the puddles of water. Ask:"If we leave our puddles of water
in the spots we chose around the room, what do you think the puddles will
look like in one hour? What will happen to the water? Will the puddle be
the same size? Will it be larger or smaller?"
After about one hour has passed, have each pair check their puddles. Each
pair should make a orange circle around their puddles if the puddles have
changed any. (The puddles should shrink.) The different groups can compare
puddles. Have each pair leave their plates and puddles where they are for
one more hour. During this time compare the predictions the children made
about what they thought would have happened to what actually happened.
Also discuss what the students think will happen to their puddles in the
next hour. Ask:"What will your puddles look like in one hour? What will
have happened to the water? Where does the water go? Do you think there
will even be a puddle left? Why?"
After one hour, recheck the puddles. Each group should make a black circle
around the new puddle. The groups can compare the puddles again. Have a
discussion about what happened to the water. Some possible questions to
ask are: If there are differences in how fast puddles in different parts
of the room evaporated, discuss reasons for that:"Who's puddle shrunk,
or evaporated faster? Why? (Relate this to the locations in the room).
What happened to your puddles? Where did the water go? What types of places
helps evaporation to happen faster?" The teacher will want to direct the
students, if necessary, to the idea that water goes into the air and that
we call this process evaporation. Have the students leave their
plates where they are overnight, so that they can check them again in the
morning. Ask : "What do you think the puddle will look like when you come
back to school next time?"
In front of the class, take a dry sponge and squeeze it to show that there
is no water in the sponge. Ask: "How much water is in the sponge?" Holding
the sponge in the air and using a tablespoon, slowly pour water onto the
top of the sponge one tablespoon at a time. Have the students count aloud
the number of spoonfuls you adding. While doing this ask: "What is happening
to the water? Where is it going? What do you think is going to happen as
I keep filling the sponge with water? Can I put water into this sponge
forever? Will we be counting forever?" Keep adding water by the tablespoon
until the sponge is saturated and starts to drip water. Ask: "What has
happened to the sponge? Why is water dripping from the sponge? Pretend
the sponge is air, what does the water dripping from the sponge act like?
(rain or a cloud) Does anyone know another name which means something is
full of water like the air or the sponge?" (If no student knows saturated,
then explain: "When air is full of water like the sponge is full, we say
the air or the sponge is saturated.) Record on the board : sponge
full = ? spoonfuls of water.
Ask the students : "Can you tell me how many tablespoons of water I poured
into the sponge when it was only halfway full of water?" Record on the
board : sponge 1/2 full = ?/2 spoonfuls of water. Ask the students : "How
many spoonfuls of water were in the sponge when the sponge was empty?"
Record on the board : sponge empty = 0 spoonfuls of water. Ask the students
: "How many tablespoons of water would be in the sponge if the sponge were
nearly ready to rain or drip? How many tablespoons of water would be in
the sponge if it were nearly empty but not totally empty?" Explain: We
can now use our scale to measure how close our sponge is to raining. Weatherpeople
can measure how close the air is to raining by using a humidity scale.
Next to the scale for the sponge, make a corresponding scale for air labeled
Introduce that weatherpeople can measure the amount of water in the
air or the humidity using instruments called humidity detectors. If available,
pass around a humidity detector for the students to examine otherwise bring
in a picture to show the class. Ask the students : "Have any of you ever
watched the news in the evening and heard the weatherperson give a value
for the humidity?" Explain that the weatherperson may use an instrument
like the humidity detector to determine the amount of water in the air
or the humidity. Have the students record humidity values in their weather
journals. The humidity values should be taken at the same time every day
- afternoon works best. If available, measure the humidity using the humidity
detectors, otherwise the values can be obtained from a radio or tv news
The next day, have pairs observe their plates and puddles. Ask : "What
happened to the water? Where did the water go? What is the name for water
going from liquid into the air? (evaporation) What is the name for water
that is in the air? (humidity) How do we measure the amount of water in
the air? (humidity detector)" Review how the air acts like a sponge to
soak up water. Like the sponge, the air can hold only so much water. Ask
: " What kind of weather would you expect to happen if there was a lot
of water in the air or high humidity? What kind of weather would you expect
to happen if there was very little water in the air or low humidity? What
kind of humidity values would you see on cloudy or foggy days? What kind
of humidity would you expect to find on a clear and sunny day? How would
you dress or prepare for school on a high humidity day?"
Discuss: When we left our plates with puddles out overnight and came back
the next day, what did we find? What had happened to the water? Do you
think the humidity in the room changed overnight? How? Why? Do you think
the humidity outside changes when you hang your wet clothes outside to
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