Explain Today's Lesson
Body of the Lesson
|Students listen and observe as factual material is presented by the teacher with the aide of the computer web site presentation. Students are presented with the experiment guidelines and are asked to hypothesize as to what will happen and why. Guidelines include setting up and conducting the experiment and recording the results. Afterwards they will be asked to form conclusions from their observations.|
|Learners & Context|
|Room Setup||Media Used|
|Standard science classroom equiped with a computer with internet access linked to an overhead projector.|
|To Bring||To Do Ahead|
|Materials: 1 large empty Pyrex jar 1 Cup of very hot water 1 metal lid or pie tin to cover the jar 1 empty tin can full of ice cubes 1 flashlight.||Rehearse experiment|
Motivation: Instructor ask the class to think back to the last time it rained. The streets were wet and puddles formed. What became of the water in the puddles? It dry up, yes but what exactly does that mean? It changed form. Like the way boiling water turns to steam but the water in the puddle didn't boil. It just slowly evaporated. But the same thing happened; the water became water vapor.
Explain Today's Lesson
Overview: The main principles and theories of the days lesson are touched upon. a) Water can exist in three states: a liquid, a solid (ice) or gas (water vapor). b) When water transforms from a liquid into a gas we say that evaporation has occurred. c) Water vapor condenses back into liquid. d) We'll conduct an experiment that will, we hope, show how clouds form and rain falls.
Body of the Lesson
a) 70% of the Earth's surface is covered with water: oceans, lakes and streams. Some of this water is evaporating or changing into a gaseous state called vapor. In warmer weather and tropical climates the process speeds up. Liquid water can evaporate at a wide range of temperatures. When water is boiled it is easy to see the vapor in the form we call steam. Most of time water evaporates without our noticing. Water can exist in three states: as solid, ice; as a liquid, water; and as a gas, vapor. The difference lies in how tightly the molecules are pack together and how fast the water molecules are moving. Molecules of water vapor are fast moving and far apart. That makes water vapor hard to see. When the temperature is high or the pressure is low molecules want to spread apart into vapor When temperature is low or the pressure is high molecules pack tightly together as water or as ice. Ice form at 32 degrees Fahrenheit, or 0 degree centigrade. Water boils at 212 degrees Fahrenheit or 100 Centigrade. Water can evaporate at any temperature between the freezing and the boiling points. How quickly evaporation occurs depends on pressure and temperature. Remember last time we talk about air having mass? Well, that's what is meant my air pressure. The air pressing down varies slightly from hour-to-hour and place-to-place. It effects the rates of evaporation and condensation. c) What is condensation? That is when water vapor turns back into a liquid state. Why does it do that? Because of a change in either temperature or pressure or both. The point at which vapor condenses and turns back into water is called the Dew Point. Unlike boiling point and freezing point which stay the same, the Dew Point varies with temperature and pressure. Dew point is important in predicting fog.
Rain Cloud in a Jar Experiment: Materials needed by each group: 1 large empty Pyrex jar 1 Cup of very hot water 1 metal lid or pie tin to cover the jar 1 empty tin can full of ice cubes 1 flashlight. Procedure: Pour about 1/2 cup of hot water into the jar and cover the jar so that the steam is captured inside the jar. Place the tin can on top of the jar and fill it with ice. Students will observe and record what is happening inside the jar. A cloud should appear inside the jar. The flashlight will help show the cloud more clearly just as the sun illuminates real clouds. In the beginning the cloud should appear white and then turns gray. This happens because as the cold air above cools the cloud the droplets within the cloud combine and grow larger partially blocking out the light from the flashlight. When the droplets become large enough they become too heavy to float in the air and fall as rain or roll down the side of the jar. When drops become large, heavy and fall it is called precipitation. In nature, drops form around a dust, pollen or salt particle called a nuclei Source: Teaching Children About Science by Elaine Leverson Students answer questions or complete a questionnaire: Was the hypothesis correct? If yes, why? If no, why not?
Summary: Students reform as a large group and report the result of their experiments with the prompting of their instructor and the instructional website. Remotivation: Congratulates the students on the success of their experiments and on their conclusions. Instructor summarizes the main points of the lesson.
Closure: Instructor asks them to think about how the things we've studied effect the weather especially the variety of clouds and storms. Instructor tells the class the lesson is over.