Relative Humidity Indicator
The hygrometer contains a humidity sensitive element that absorbs and disperses the humidity (moisture) in the air around it.  In this case, the element is a small spiral floating in fluid.  The spiral winds and unwinds as the moisture from the surrounding air is absorbed or released.  This motion is transferred to the indicator hand, which moves on the reading surface.  It takes approximately four hours in a fairly windless atmosphere for the indicator to relate the change in humidity level.

Students will read a hygrometer and understand that the amount of moisture in the air changes as weather conditions change.

Instructions for Set Up
The hygrometer may be wall mounted or placed in the area where the relative amount of moisture in the air is to be measured.  Although accurate for this type of mechanism, all hygrometers except a sling psychrometer show only approximate readings.  It takes several hours for the hygrometer to change readings if it is moved to a more or less humid atmosphere.  It is to be used only indoors.  It is most accurate away from heat or cold sources and out of a breezy area.

Activity:  It Feels Like Summer

Objective:  Students will accurately read the humidity of the room and of the air in a humidity tent, understanding that humidity is moisture in the air.

Humidifier (warm or cool moisture)
Clear plastic to cover desk or table and drape to floor for a tent.
Time: 15 minutes to introduce hygrometer and note room humidity
40 minutes (after the hygrometer has been in the tent for several hours) for children to experience the tent
40 minutes to meet, discuss, and fill out recording sheet

Background Information:
The mechanism in a hygrometer measures the amount of moisture in the air.  When there is less humidity, the air feels lighter and is easier to breathe.  When the relative humidity is higher, the air feels heavy and moist.  It is harder to breathe.  When the air is hot and humid in the summer, most often the moisture is evaporating as part of the water cycle.

In a whole group, discuss humidity as the amount of moisture in the air.  Relate the moisture to the water cycle.  Show the students the hygrometer and discuss how it works.  Have them read it and begin their recording sheets.
    Set up the humidity tent.  Place a room type humidifier under a desk or table and turn it on.  Place a large sheet of plastic over the desk.  It should fall to the floor to create a fairly closed tent.  Place the hygrometer in the tent, but well off the floor.  Let the humidifier work for three or four hours.
    Have small groups or individual students sit for a few moments in the tent and read the hygrometer.  They can then fill out the next portion of their recording sheets.
    After all the children have experienced the humidity tent and filled out the beginning of their recording sheets, meet once again as a whole group.  Have them share their personal observations about the two atmospheres. Expand the discussion to climates.  Where is the air always very humid? (rain forests)  Where is the air always very dry? (deserts)  What are these two places like for man and living things on the earth?

Math Extension:  Pie Graphs
Use the work sheet to have students relate the percentage of humidity in the two atmospheres to a visual, pie graph presentation.

Hygrometer Recording Sheet
Name ___________________

Atmosphere 1:  In your classroom

The relative humidity is _____________%.

Atmosphere 2:  In the humidity tent

The relative humidity is _____________%.

Which felt better to breathe?__________________ because


What kind of weather would there be if the hygrometer said 100% humidity?  _____________

Pick a city and state you would like to visit.  ________________

What do you think the relative humidity would be like there?  Would it be fairly dry?  Fairly wet with lots of rain?  Why do you think that?

 Barometer  Rain Gauge  Anemometer  Probe Thermometer

This curiculum project was funded by the Colby Partnership for Science Education, the Howard Hughes Medical Institute, and the Bell AtlanticFoundation