Air+Pressure

= Air Pressure =
 * Grade Level and Topic: ** Grades 6-8

Amelia Ahnert (aea5125@psu.edu)
 * Names and Contacts: **

Lindsey Anderson (lta5008@psu.edu)


 * Educational Standards: **
 * ** 3.2.7B- ** Apply process knowledge to make and interpret observations
 * ** 3.5.7D- ** Describe factors that effect evaporation and condensation
 * ** 3.5.7C- ** Describe basic elements of meteorology


 * Instructional Objectives: **

As a result of this lesson students should


 * Describe the power of air pressure and it's effects
 * Explain what causes the drop in air pressure
 * Relate the change in air pressure to observations of water being sucked into can


 * Content Explanation: **

This demonstration-based lesson is on air pressure. This force exerts 14.9 pounds per square inch. This can be visualized with a piece of printer paper, which has over 1,393 pounds being pushed on it by air. The reason that this doesn't feel heavy is because the pressure is distributed evenly across its entire surface (including the bottom). The air pressure is balanced out but, if you were able to get rid of the pressure pushing on the bottom of the sheet, it would weigh the amount described previously (1,393 lbs.). This is the same idea that is used for this demonstration with the aluminum can. Originally the air exerts a force on the inside of the can to balance out the air pressure outside. When water evaporates inside of the can, the vapor that is produced replaces the air inside. This vapor exerts an equal force still to the air pressure outside the can. When the temperature is cooled quickly, the vapor condenses and there is a decrease in pressure inside the can. This causes the more dominating outside air pressure to crush the can. You may notice that some water gets sucked up into the can when exposed to the cold water. This is because the vapor inside has condensed and there is room in the can for the water; however, the water doesn't t replace the vapor fast enough to prevent the outside air pressure from crushing it.


 * Administrative Considerations: **

There are no chemicals or hazardous materials being used in this lab. It is important to tell students to be careful with water around electronics and to make sure they do not touch the hot plate. Another area to be cautious with is the aluminum can will heat up when placed on the hot plate to boil the water. It must be handled with the use of tongs to prevent burning.

This lesson uses different learning strategies including verbal instruction, discussion, demonstration, and written explanations in an effort to include multiple types of learners. Students will record their observations on a worksheet. The observational nature of the lesson should facilitate the understanding by ELL/ESL students.


 * Materials: **


 * ·Posters (premade with several diagrams on them)
 * ·Clean, empty soda can
 * ·Hot plate
 * ·Tongs
 * ·600 or 100 ml beaker
 * ·Cold water (preferably with ice)
 * ·Oven mitt and safety goggles


 * Preparation Required: **
 * ·Turn on the hot plate to get it ready before you start the demonstration
 * ·Mix the ice and water together in the beaker
 * ·Remove tab from soda can
 * ·Photocopy worksheets (enough for each student)


 * //__ Body of the Lesson: __//**


 * Predict: ** (8 minutes)

Introduce ourselves, learn kids name

// Do you know what air pressure is? Why do you think air pressure is important? Etc. //

We plan to basically ask several questions to assess the students' prior knowledge.

Using the posters prepared before class, discuss what exactly air pressure is and how it related to the weight of everything around us. // If you removed the air pressure from beneath a simple piece of paper, it would weigh over 1,393 pounds. This is because air pressure exerts a force of 14.9 lbs/inch2 and without the air pressure below balancing the air pressure from above; you would only feel the weight due to the air pressure above the piece of paper. Air pressure has a habit of moving from areas of high pressure to areas of low pressure. It is this natural process, called the PRESSURE GRADIENT FORCE, that drive the Earth's weather patterns, from simple breezes to tornados and hurricanes. We will be demonstrating this PGF throughout the course of this demonstration. //

// There are several things you can do to decrease or increase the air pressure in a certain location. One way to decrease pressure is to increase temperature. Why do you think this is? //

// If we heat a little bit of water inside a can in order to fill the can with water vapor, what do you think will happen? If we were to then stick that can into a beaker filled with cold water, what do you think would happen then? Why? //


 * Observe: ** (5 minutes)


 * 1)  1.Fill the 600 to 1000 ml beaker with cold water and some ice if available. The water should be very cold.
 * 2)  2.Put about 15 ml (1 teaspoon) of water in the soda can and place it on a heated up hot plate.
 * 3)  3.Allow the can to sit on the surface of the hot plate until water vapor starts coming out of the whole in the can. (The water in the can should be boiling)
 * 4)  4.Once vapor starts coming out the top, allow the water to boil for an additional 30 seconds.
 * 5)  5.Using tongs, grasp the can and quickly invert it and dip it into the beaker filled with water.
 * 6)  6.The can should collapse almost instantaneously.


 * Explain: ** (5 minutes)

After the demonstration, ask the students for their opinions about what they just observed. // Why do you think the can was crushed when dunked in the cold water? Do you think this will always happen? How can we modify this experiment to test your hypothesis? //

Allow the students to fill out their worksheets based on what they observed.

// Explain why the can was crushed. //// What caused the can to collapse? When you heated the can you caused the water in it to boil. The vapor from the boiling water pushed air out of the can. When the can was filled with water vapor, you cooled it suddenly by inverting it in water. Cooling the can caused the water vapor in the can to condense, creating a partial vacuum. The extremely low pressure of the partial vacuum inside the can made it possible for the pressure of the air outside the can to crush it. //

// A can is crushed when the pressure outside is greater than the pressure inside, and the pressure difference is greater than the can is able to withstand. You can crush an open aluminum can with your hand. When you squeeze on the can, the pressure outside becomes greater than the pressure inside. If you squeeze hard enough the can collapses. Usually, the air pressure inside an open can is the same as the pressure outside. However, in this experiment, the air was driven out of the can and replaced by water vapor. When the water vapor condensed, the pressure inside the can became much less than the air pressure outside. Then the air outside crushed the can. //

// When the water vapor inside the can condensed, the can was empty. You may have expected the water in the pan to fill the can through the hole in the can. Some water from the pan may do this. However, the water cannot flow into the can fast enough to fill the can before the air outside crushes it. //

Ask final questions to test their knowledge of the material.