Humidity: How and Why

How We Measure It & Why It Matters (Science Club/Weather series of posts)

Wednesday, Mar 15

do Static Electricity Experiments
Dining Room - station 1
balloon, wall

Bathroom - station 2
plastic pen, wool sweater, a thin stream of water from the sink

Library - station 3
plastic pen, wool sweater, 3 hole punch, sheet of copy paper

explain static electricity and how it works

consider the positive end and negative end of a magnet, and look at how they are attracted to or repel one another

note that the term 'electricity' comes from elektron, which is the Greek word for "amber" and think about what that connection might be (early triboelectric experiments in Ancient Greece)

the prefix tribo means "rubbing" in Greek, so 'triboelectricity' means electricity resulting from rubbing

explain why static electricity experiments work better in the winter when humidity is less

look up the humidity outside at the present moment

let children design their own humidity experiments (dishes of water with food coloring or sugar dissolved in them, left out covered or uncovered, left in places in the house of different temperatures)



even though they know that humidity means water dissolved into the air, it's helpful to watch it happen firsthand!

they are interested in how quickly it will happen, what else will evaporate up along with the water and what will be left behind (sugar? food coloring?), and if water can get out of a closed container

Wednesday, Mar 22

Today we checked up on the results of our experiments. A lot of interesting things happened, actually! Some of them I knew would happen and some of them I didn't:


Water goes up. Sugar stays behind. This was an expected result, but still fun to see all the crystals down on the bottom of the cup.

Notice that the line on the side of this cup is the original water level as of one week ago. So we learned that adding the lid slowed down evaporation, but did not stop it.

Food coloring also stays behind (which we all expected).



BUT, from other experiments (each child designed his/her own), we also learned that adding food coloring to water makes it evaporate more slowly! We went and checked the ingredients list in food coloring, and hypothesized that the food coloring ingredients make the water more viscous and thus it evaporates just a tad more slowly.

AND one group checked to see if stirring in -- or not stirring in -- the food coloring made a difference in the evaporation rate. And it did! I would have never ever thought to investigate that. Children are so marvelous.

The cup of water which was placed in the fridge also evaporated more slowly than the one on the countertop, and we had a few ideas as to why that could have happened.

- the temperature being colder ?
- the refridgerator being a closed system ?
- do fridges have humidity controls as well as temperature controls ?



The children had to first observe the results of their experiments, draw sketches and make notes in their Science Notebooks, and then give a short summary of their results to the class.




All of that took longer than I expected, so instead of beginning to make hygrometers using human hair, we just went over the experiment protocol and I explained how we would build the hygrometers. As it turns out, they are not interested in making one, so we just ended the class with a discussion and a diagram of how you would set one up. Since human hair does respond to humidity, it makes a surprisingly accurate hygrometer! You calibrate it by blowing a hairdryer on it until the length of the hair stops changing (and mark that line as 0% humidity) and by placing it in a closed plastic storage container with a sponge saturated with water until length of the hair stops changing (and mark that line as 100% humidity). Amazing!

Make a Hygrometer with 3 Strands of Hair - Science Buddies

Wednesday, Mar 29

wrap up humidity by showing our new weather stick and explaining how it works (Can A Stick Really Predict Good Weather?)



have students work in pairs to make a K-W-L chart for Clouds

do Make a Cloud in a Jar experiment (method 1)

NOTE: Our conversations about humidity really came in useful when we hatched baby chicks in the classroom in April!

our previous exploration: wind speed

our next exploration: rainfall

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