Middle school students should be ready to collect, organize, and and display data. Weather projects offer good data for charts and tables and address many key science concepts.
The Purpose of the Science Project
Few people understand how relative humidity is determined, but the process is very simple. Evaporation occurs slowly when air is already damp and rapidly in dry air. Since evaporation cools a thermometer, the amount of cooling on wet thermometer bulb will be less when the air is wet and more when the air is dry. A comparison of the two temperatures using a wet-bulb, dry-bulb table gives the relative humidity.
Materials for Science Project
The student will need:
- 1 thermometer — either a pocket type or a glass type like those in science labs
- small amount of Kleenex or toilet paper
- three-panel poster
- three or four feet of fishing line or strong string
- a small container with a few ounces of water
Science Fair Project Procedure
The thermometer readings should be taken three times on the same day — morning, once from 7:00 AM to 8:00AM; once at midday from noon till 1:00 PM; once after sunset about 7:00 PM till 8:00 PM. The poster will take another hour or more depending on how much time is given to neatness and organization.
For each reading session a wet-bulb and a dry-bulb temperature should be taken and recorded using the following procedure. Since humidity varies more outside than inside it is important that the readings be outside on a clear day when no predicted major changes in weather are forecast.
- For each pair of readings — wet-bulb and dry-bulb — proceed as follows:
- For thee morning reading, after the thermometer has adjusted to outside temperature — allow five minutes or more.— record the temperature as the dry-bulb temperature.
- Wrap the bulb or stem of the thermometer in a no more than two layers of tissue and wet it. The paper will stay in place once wet.
- Tie the line or string securely to the top of the thermometer to so that it can swing freely. If string is not available, hold the thermometer firmly at the top and swing it back and forth or in a circle to allow air to flow over the wet bulb. Record this as the wet-bulb temperature.
- .Repeat steps #2 - #4 for the midday and nighttime readings.Use a wet-bulb, dry-bulb table to determine the relative humidity for each time.
Discussion of the Science Project Results
The term “ relative humidity ” is used because humidity — water vapor in the air — depends on, or is relative to air temperature. Cool morning air typically has a high relative humidity because cool air has lost the necessary heat energy to evaporate lots of water. This is why there is dew in the morning — the previously evaporated water molecules in the air slow down and stick to each other and objects and form liquid water.
The dew evaporates as the air warms up adding heat energy to the water molecules and become water vapor again and the capacity of the warmer air to “hold” more water vapor increases, so the relative humidity drops.
When darkness comes, the air temperature drops and the daily cycle begins all over with the formation of dew which continues to condense as long as the air cools. Rainy or foggy days will typically have high humidity all day as indicated by the moisture continuously condensing.
Warm, muggy days will have humidity from 40% to 60% at midday. The muggy feeling indicates that water on the body does not quickly evaporate because the air already has lots of moisture and the body is not losing heat fast enough to cause perspiration to evaporate and cool the body — the function of perspiring is to regulate body temperature.
This project can be strengthened by taking three readings at the same time on a day that is rainy and cooler and comparing the results of a clear day with a rainy day.
Displaying the Results of the Science Project
A review of the scientific method is a good idea. The hypothesis should be an “If… then…” statement — i.e., “If relative humidity is measured in the morning it will lower at midday and go up after sundown.” This is only an example and students are encouraged to make their own. There should be no penalty for an incorrect prediction, since the experiment produces knowledge in any case.
A bar graph should show the recorded humidity changes over time. Time is usually placed on the horizontal axis with humidity reading displayed on the vertical axis.
Neatness is usually part of a scoring rubric for a science project. The graph should be in the center panel. A prominent project title should be included.
A few photographs of the experiment help people understand what was done. These can be displayed on the right side of the panel.
Weather experiments are good because they are often easily done and yield good data for tables and graphs. Students should always follow the experimental method for any scientific investigation.
Source:
- “Welcome to Science Fair Project World!” (Accessed October 26, 2011)
Harvey Craft - I am a retired educator with diverse experience. I read anything science, education, and history. I write to share what I learn.
