Lesson 4 of 14
Objective: SWBAT 1)describe and define gas pressure, 2) explain what causes air pressure 3) complete simple air pressure calculations
Teaching students about air pressure can be challenging as you need to give them multiple opportunities to look for evidence of air pressure around them. In this series of activities students make observations to show how air pressure is that work in a variety of situations.
To set this activity up I suggest that you set up stations around the room. Begin with a demonstration at the front of the class to pique their interest in and explain to them how they will rotate through various stations and record your observations. As this lesson is quite full, you may want to video tape the demonstrations to use as an activator if the lesson extends into a second day.
Some of the key terms that you're going to cover in this lesson include:
- Clear plastic cup
- Index card
- Drinking glass
- Crumpled ball of paper
- Pair of clean toilet plungers
- 2 L plastic bottle
- Large plastic syringes
- Large tubs or a sink to catch the spilled water
- Students work on inferring ideas about the relationship of gas, volume and pressure.
- Students make observations of air pressure affecting different substances.
What kid doesn't love balloons? A great attention grabber for this lesson is to blow up a balloon and let it fly. I happen to use Rocket Balloons* as they are bright, loud and really zip around the room.
Once students calm down a bit, ask them the following questions:
- Why does the air leave the balloon?
- What makes the balloon fly faster or slower?
- Could air pressure have something to do with what you've observed? If so how?
Follow their responses up with questions about what they think air pressure is and how it may be related to weather.
*Note: These do contain latex, so check for allergies!
Since this lesson involves several stations you may opt to spread it over a couple of class periods. Alternatively you could perform the demonstrations of your choosing in front of the class and have students observe and record in their journals.
Be sure that students have ample time to record their observations and I always suggest to my students to include both drawings and annotations along with their observations in their journals.
For each of the observations make sure that students are paying attention to the presence of air pressure both inside and outside of each container. Before they begin demonstrate how to use arrows to indicate the direction and origin of air pressure. If they believe that there is greater pressure in certain areas have them add additional arrows.
- Balloons (several)
- 2 liter bottle
Push a deflated balloon into a bottle and stretch the open end of the balloon back over the bottle's mouth.
- Two clean plungers
Line up the bottom of two plungers and press them together until all the air is gone then try to pull them apart. Not so easy huh?
How might air pressure be causing them to stay stuck?
Fill a clear plastic cup with water. Place a laminated card over the top of the cup. Hold the card to the mouth of the cup and invert over a plastic tub. You can now let go of the card—it remains suspended, and the water does not spill out.
Why doesn’t the card fall?
- Plastic syringe
Have students do the following:
With the cap off, remove the plunger from the syringe barrel. Place one mini marshmallow inside the syringe, leaving the cap off. Choose a second marshmallow of the same size to serve as the control.
Place the plunger in the syringe barrel and push it in, forcing out as much air as possible without squeezing the marshmallow.
Place the cap on the tip of the syringe. Pull the plunger, hold it in the out position and observe. (The marshmallow expands.)
Compare the size of this expanded marshmallow with the size of the control marshmallow.
Predict what will happen if the plunger is released. Release the plunger and observe.
Have students record in their journal why they think the final size of the marshmallow is smaller than its original size.
This activity helps illustrate the pressure volume relationship of the gas, known as Boyle's Law. Boyle’s Law states that volume varies inversely with pressure at constant temperature and constant amount of gas; therefore, as volume increases, pressure decreases. Likewise, volume decreases, pressure increases. In the closed system of the syringe, when the plunger is pulled out, volume increases in the pressure inside the syringe decreases.
It is likely that there will not be enough time on the same day to sufficiently explain what students observed at each station. Don't skip the conversation! If not on the same day, the next day. If you video tape a demo of each of these activities, it's a great activator for the next lesson.
Facilitate discussion with your class and ask them to explain their evidence showing that air pressure existed in each of the demonstrations. This is an important time to check for understanding and push student thinking by asking them to tell you more about their explanations. Making connections between the demonstrations offers another route to scaffolding students' who are struggling with making the leap from the concrete (visual) to the elements that aren't visible. You want to come away from this discussion having a better understanding of what they think air pressure is and how these demonstrations help them understand.
I like to use this time as well to have students come up and show me their thinking by drawing on the board or I also have a set of individual whiteboards and dry erase markers that I hand out to the students occasionally so they can draw what they're thinking, hold that up to the class and present to us their ideas.
Helping students make their thinking visible is an important tool both for you and for them in building comprehension and understanding. Make sure at this time if you use a strategy to have students include arrows to indicate the direction of force in the amount of force. It may be necessary to ask them to several arrows as they may only want to include one in their explanations. For example the air pressure outside of the balloon would be coming from every single direction.
In the first demonstration, there is air already present inside of the 2 L bottle. As students attempt to blow air into the balloon inside the bottle, they're pushing against the pressure of the air inside the bottle.
In the second demonstration, when the glass is inverted into the water, there is already air inside the glass. This air only prevents the water from filling up the inside of the cup, keeping the crumpled paper dry.
In the third demonstration, the two plungers are difficult to separate because once the air between them is evacuated the surrounding air pressure is pressing the two plunger heads together.
In the fourth demonstration, the air pressure of the air in the room pushes up on the card; this is greater than the weight of the water pushing down on the card.
In the fifth demonstration, as the air outside of the marshmallows is removed the air trapped inside of the marshmallow expands. Air pressure in these little pockets inside the marshmallow equalizes with the air pressure outside the marshmallow. Some of the air pockets will break, so when air is put back into the chamber the marshmallows may be smaller than they were initially.
On the next day I present my students with an Air Pressure challenge. Working in pairs, they have 15 minutes to design a simple demonstration, with with a diagram, that shows the presence of air pressure. I give them access to anything in the lab (within reason). I do not let them use any of the demonstrations that we have already seen, but they can use these as inspiration for their ideas.
In the images below you can see students working out ideas using a plunger, a water bottle rocket (which they remembered from 5th grade science), and other materials.
Below are two student demonstrations.
As a follow up to this lesson and to provide a check for understanding, I use a thinking routine to prompt students to share their ideas on air pressure.
I begin by creating three posters with the following titles:
- What I understand about air pressure.
- What I still don't understand about air pressure.
- What I am wondering about atmospheric pressure.
I post these around the room before class and then you can begin or end class by asking kids to write a response to each prompt on a sticky note and place their response on each poster.
This helps to make their ideas visible, reveal any misconceptions, share what they understand and open up new area for study. Below are some sample responses.