February 11, Weather and Water Investigation 6 Day 6

Transcription

1 Weather and Water Investigation 6 Day 6

2 What is dew point? Bell Work

3 Response Sheet: Water In The Air Answers When we put water on our hands and waved them in the air, our skin felt cooler. That's because when water evaporates it needs energy to get the molecules moving fast enough to escape the liquid water. The energy transfers from your skin and the surroundings to the liquid water. So when the water evaporates, you feel cooler. Sweat contains water, so it works the same way.

4 Dew Point Data By Class February 11, 2013

5 Knowledge Builders 40. Some people refer to condensation on a cold glass as dew. What is dew? Droplets of water seen on plants and other surfaces, usually in the morning. 41. How does dew form? Surfaces cool to the temperature that lets water vapor condense into droplets.

6 Knowledge Builders 42. The temperature at which water changes from a gas to liquid - the temperature that you determined experimentally - is the dew point. Dew point is the temperature at which air is saturated. Dew-point temperature is not the same everywhere, so you always have to figure out the dew point for the area you are interested in at the time. 43. Dew point depends on the amount of water vapor in the air. If a lot of water vapor is in the air, you don t have to lower its temperature much to reach saturation. If very little water vapor is in the air, however it must be cooled to a very low temperature for saturation to take place.

7 Vocabulary 8. Dew Point - the temperature at which air is saturated.

8 Dew-Point Questions Answers 1. Dew point is the temperature at which water-vapor saturation occurs in air. Any additional drop in temperature will cause water vapor to condense as liquid, forming dew, fog, or clouds. Dew point helps meteorologists predict the weather, particularly whether it will be rainy, foggy, or cloudy. 2. Dew would not form if the air were dry - very low humidity - unless the temperature got extremely low. Dew would not form if the temperature did not drop low enough to reach water vapor - saturation. Dew would not form if it were windy. 3. It would probably form as frost instead of dew.

9 Dew-Point Questions Answers 4. The glasses must be colder than the air in the house. Energy from the air transfers to the glasses. This reduces the temperature of the air in the vicinity of the glasses. If the temperature drops below dew point for the air in the house, condensation will occur on the available surface, the glasses. Solution: warm the glasses above the dew point before putting them on in the house. 5. Dew point can change, depending on the humidity in the air. The air has to be saturated before condensation can happen, so when there's less water vapor in the air (humidity), the air is saturated at a lower temperature. You could do the dew - point investigation on different days when relative humidity has changed to see if the condensation temperature (dew point) changes.

10 Handouts: Dew-Point Questions Teacher Notes Materials: Knowledge Builders, Response Sheet: Water In The Air, results from condensation activity. Procedure: 1. Check over Bell Work - We will not give a full answer until later. 2. Check over homework - Response Sheet: Water in the air. 3. Have one student from each group come up and write the result of their condensation activity on the board (a difference for 3-4 degrees is expected). 4. Average the numbers and write on the board. The average is the temperature at which water vapor condenses on this day, at this time, in the classroom. 5. Go over Knowledge Builders. 6. Work on handout in groups: Dew-Point Questions 7. Go over questions in class. 8. Collect questions. Homework: Study over Weather and Water Investigation 6 Knowledge Builders and Vocab.