Moisture in Your Everyday Life
The questions on the next several pages are related to real life experiences that you have had or may encounter at some time in your life. Answer as many questions as you can as completely as possible in the time provided. You should work with at least one other person. Your group will be given a specific question number to start with. At the end of the allotted time each group will discuss their answers.
1. You live in Kansas and it is January. Your clothes dryer just broke and you have to hang your clothes out to dry on the clothesline. The weather conditions indicate a temperature of 40 (F and a dewpoint temperature of 20 (F. Will the clothes dry? Explain.
Yes, the clothes will dry. Clothes dry when water evaporates from them. As long as the air is not saturated, water can be evaporated into it. Once the air is saturated it contains as much water as it possibly can (for that temperature) and you cannot add any more vapor into the air. The clothes will dry because the dewpoint and air temperature are far apart, indicating that the air is far from being saturated.
2. Explain why does it take longer for vegetables to cook at higher elevations. (Hint: consider the elevation and the temperature at which water will boil)
At the surface, the boiling point of water is 100 (C (212 (F). As water boils, bubbles of vapor rise to the top of the liquid and escape. The saturation vapor pressure exerted by the bubbles must equal the pressure of the atmosphere, otherwise the bubbles would collapse. So, boiling will only occur when the saturation vapor pressure of the escaping bubbles is equal to the total atmospheric pressure. As you move to higher elevations, air pressure decreases. This means that you will be able to get water to boil at lower temperatures (92 (C). Recall that SVP is related to temperature. Lower temperatures produce lower SVP. Once water boils, the temperature remains constant. If you continue to heat the water, the energy is used to convert the liquid water to water vapor. Because the vegetables are boiling at a lower temperature, they will have to boil longer to cook thoroughly.
3. Would you expect water in a glass to evaporate more quickly on a windy, warm, dry summer day or on a calm, cold, dry winter day? Explain.
The water would evaporate more quickly on the summer day. The windy conditions will enhance evaporation (as opposed to the calm winter day conditions.) Both days are “dry”, however they are very different temperatures. The air has a larger capacity for water vapor at higher temperatures and so more water will evaporate into the air on a warmer day than a colder day.
4. If you take a hot shower in the bathroom, the mirror will fog up. Explain why this happens. Explain why aiming a stream of air from a hair dryer at it will make the mirror clear again.
With the hot shower on, you are increasing the dewpoint in the bathroom as water evaporates from the stream of water from the shower into the air. When the amount of water vapor in the air is the maximum amount possible, then the air is saturated (the dewpoint temperature = air temperature). At this point, adding any more vapor into the air will cause condensation to occur. Water droplets begin to condense on the mirror (they are easy for us to see but they are condensing on all the surfaces in the bathroom). If you blow air over the condensed water, evaporation will start to occur. If the air is warm, the saturation vapor pressure of the air near the mirror will increase, thereby decreasing the relative humidity and causing evaporation to occur.
5. Two people with long thick hair live in different parts of the country; one in Arizona and one in North Carolina. In the summer if they both wash their hair and leave it to air-dry. One will have dry air within an hour while the other persons hair not dry all day. Whose hair will...
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