WHEN MOISTURE COMES OUT OF THE AIR 



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TEST OF MASTERY OF THE TOPIC 



In your notebook complete the statements, answer the 

 questions, and comply with the instructions. 



1. List three factors which aid evaporation. 



2. When water or other (solids, liquids) evaporate, 



the surroundings are (warmed, cooled) because (heat, 



cold) aids evaporation. 



3. List three factors which hinder evaporation. 



4. Boiling is rapid (evaporation, condensation) , 



5. A simple device that measures relative humidity is 



called a . The dry bulb reads than the wet bulb 



because . Evaporation from the wick is controlled by 



the in the air. 



6. Give several examples of cooling by evaporation. 



7. A day that is good for drying clothes should be (warm, 



cool) 



and (still, windy) 



with (low, high) 



relative humidity. 



8. On a certain day the relative humidity was found to 

 be 70 per cent. This means that the amount of moisture 



actually was only per cent of the which it 



could at that temperature. 



9. Evaporation body temperature because of the 



effect produced by the of from its surface. 



10. In some hot and dry countries water is kept cool 

 by placing it in a porous earthen jar through which some 

 of it can slowly seep. As the film of water on the outside of 



the jar , it takes the needed from the water on 



the inside of the jar, thus cooling it. 



11. From the knowledge gained in the study of this topic, 

 infer why electric fans are used on very warm days. Do 

 fans actually cool the air? 



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TOPIC 2. WHEN MOISTURE COMES OUT OF THE AIR 



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SUGGESTED PROBLEMS AND QUESTIONS 



1. What causes moisture to come out of the air? 



2. What is the water cycle? 



3. What causes the moisture that comes out of 

 air to assume different forms such as clouds, 

 dew, fog, rain, hail, and snow? 



SUGGESTIONS AND HELPS FOR STUDY 



1. You will find that answering the following ques- 

 tions will aid in the solution of the problems. You will 

 be able to answer some of them from your reference 

 study, while others will require experimentation. 



a. Problem 1 

 What is condensation? 



In what ways does condensation differ from evapora- 

 tion? 



What is the dew point? 



What is the relative humidity at the dew point? 



What causes cold water pipes and pitchers of cold 

 drinks to "sweat"? 



b. Problem 3 



What is dew and what are its causes? 



What causes fogs and clouds? 



What are the different cloud forms? 



Under what conditions are frost and snow formed? 



How are sleet and hail formed? 



2 V . You may find the following new words and 

 jikrases in this study : 

 cirrus a type of feather-like cloud formation usually 



found at great heights. See Figure 59. 

 condensation a change from the vapor state to the 



liquid state. 

 cumulus a type of cloud formation which resembles 



mountains. See Figure 59. 

 nimbus a type of cloud formation which is dark, usuallv 



rolling, from which rain or snow may come (Fig. 59). 



precipitation the moisture which comes out of the air 

 as rain or snow. 



stratus a type of cloud formation usually at low levels 

 and appearing in layers or strata (Fig. 59). 



water cycle the round through which water goes in na- 

 ture in the processes of evaporation and condensation. 



EXPERIMENTS OR DEMONSTRATIONS WHICH WILL 

 HELP ANSWER THE PROBLEM QUESTIONS 



Experiment 22. How can the dew point be deter- 

 mined? 



Secure a bright, shiny cup, such as an aluminum meas- 

 uring cup, and fill it about two thirds full of cold water. 

 Lower the temperature slowly by adding small bits of ice. 

 Stir the ice and water continually with a thermometer and 

 note the temperature of the water when mist begins to form 



Fin. 55 



on the outside of the cup. Stop adding ice, allow the mist 

 to disappear, and note the temperature. Again cool by add- 

 ing ice and note the temperature at which the mist forms. 

 The average of these three readings will be the dew point 

 for that day. 



In your notebook 1 record the notes of this experiment 

 and complete the statements given below. 



The moisture which condensed on the outside of the 



cup came from the . air can hold more moisture 



than air. The dew point is the temperature at which 



the in the air begins to On any day the moisture 



present in the air is sufficient to saturate it at the 



1 See workbook, p. 14. 



