Air Pressure: How and Why

How We Measure It & Why It Matters (Science Club/Weather series of posts)

BRAINSTORM

There are so many fun science experiments to demonstrate Air Pressure, so the first thing I'm going to do here is to compile a collection of them. That way we have plenty to choose from if the students continue to be stumped.

champagne flute, clear container of water, $10 bill, paper towel

Pins in a Bottle
disposable plastic water bottle, 5-7 push pins, water

Drip Drop Bottle
disposable plastic water bottle, small nail, hammer, water

Five Ways to Demonstrate Air Pressure to Children

Water Glass Trick
glass, water, index card

Fountain Bottle (video)
2 L bottle, clay, straw, water

Ping-Pong Funnel
ping-pong ball, funnel

The Million Dollar Bet
paper towel, soda bottle

Kissing Balloons
string, two balloons

Bernoulli Brain-Teasers (PDF)

Use Your Lips to Levitate
dollar bill

Balloons That Boggle
string, two balloons, water

Suspended in the Air Stream
ping-pong ball, flexible straw

Fool the Spool
tack, playing card, large spool of thread

Squeeze the Stream
cookie sheet, pencils, tape, plastic wrap, sink or tub, soapy water

Building a Simple Hovercraft (video)
old CD, small Dixie paper cup, cap from a plastic sports bottle, hot glue gun, box cutter, pushpin, several balloons

Cartesian Diver (video)
2 L water bottle, disposable plastic water bottle, test tube

Diving Ketchup
clear plastic soda bottle with cap, water, bowl, ketchup or soy sauce packets

I think we'll do a review of temperature and density first, then the graphing of pressure in relationship to altitude, and then the air pressure experiments. And then, from there, we can look at how a barometer works in a later week.

1) cold air is heavier than warm air - vintage science concept chart from
"Air and Weather," prepared by Donald Nasca, designed by Cynthia Amrine

Warm air rises primarily due its lower density as compared to cooler air.

2) Density of a Candy Bar Lab
$2.80 on TpT
Hershey's chocolate bar, balance, ruler

This Is Why Earth, Surprisingly, Is The Densest Object In Our Solar System

3) Layers of the Atmosphere: Graphing Temperature and Pressure (PDF)
print page 2 of PDF
graph paper, scissors, tape, pencil

we are only going to graph pressure
cut the paper in half vertically and tape it to itself to be extra long and thin

Here's Where Outer Space Actually Begins

Looking Down
by Steve Jenkins (wordless)

Gravity
by Jason Chin (ALL CAPS)

4) Air Pressure and Density in the Atmosphere (PDF)
scissors, glue stick, pencil

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Wednesday, Nov 16

recall last week's Science lesson with Aurora Lipper on exploring the deep ocean (this is being presented again on Nov 17: Marine Biology, Oceanography, and Underwater Robots)

compare Water Pressure (the weight of the water above you) to Air Pressure (the weight of the air above you)

read Otis and Will Discover the Deep: The Record-Setting Dive of the Bathysphere and lay out three 12-inch and one 18-inch ruler to show 4 1/2 feet (the length, width, and height of their sphere)



watch TED talk recommended by Aurora Lipper: How We Found the Giant Squid by Edith Widder

do Pins in a Bottle experiment

add notes to Science Club notebook (this was a sketch of our experiment protocol, observations, and further questions)

their questions and comments were VERY illuminating; so often we forget to have kids explain what they think is happening in Science... but if we don't listen to them then we are not able to fully address their misconceptions

here are some of the things they had to say:

why doesn't the water leak from the sides when the pins are in?

when you take the cap off the bottle does more air come in and punch the air that's inside and push the water out of the holes?

what's the air pressure for each layer of the atmosphere?

why does changing air pressure make people get sick?

is caisson sickness a pressure sickness with air? because it can't be water pressure because you're not actually in the water

why do people have to wear oxygen tanks on Mount Everest?

how do oxygen tanks work?

is air pressure the same as density? maybe they're cousins but not siblings

it is hard to breathe when you're higher up because the air pressure down here is keeping the oxygen from just floating up away from you

if you didn't have grass in your yard then dust bowls and tornadoes would start

what is the air pressure in a tornado?

can tornadoes or hurricanes be made out of different materials, like can you have a mercury hurricane?

a hurricane is a kind of a tornado, or a tornado is a type of a hurricane

with a hurricane the warmth and the water fuels it, whereas a tornado forms at full strength but it keeps its strength until it starts to die

the faster a hurricane's winds are the faster it dies because it is picking up so much stuff and that slows it down; when you pick up stuff that's heavy it's hard to run fast

Wednesday, Nov 30

recall the Bernoulli exhibit at the Science Center

do first four experiments from Bernoulli Brain-Teasers (PDF)

Use Your Lips to Levitate
we used Monopoly money for this

Balloons That Boggle
the children named the balloons "Romeo" and "Juliet" and told me that we were the Capulets and Montagues trying to push them apart... no matter what we did they just moved closer together

Suspended in the Air Stream
it works best to have a Ping Pong ball for each child

Fool the Spool
we used Uno cards for this
(and it is totally find to use pushpins instead of thumbtacks)




The directions for Fool the Spool are not clear as to whether you put the spool over the head of the tack or the pointed end. We decided it was the pointed end. But when we read the explanation as to why it works, it really didn't explain what the tack is for. Is it to add weight? That was the big question still remaining at the end of our session.

After each experiment we stopped and drew a sketch, and the children tried to figure out how to show what the (invisible) air is doing. It was challenging but very fun. Personally, I think that the best thing is to have different colors for different speeds of air.

The big takeaway here? When a fluid flows through a region in which its speed increases, its pressure will fall. And air is actually a fluid!

Why will the money curve upward, the balloons go toward each other, and the card stay on the spool? The faster moving air has less pressure. So the still air becomes the stronger of the two. In the Ping Pong ball experiment, you're supposed to be able to gently nudge the ball and the still air will push it back into its pocket of lower pressure. That didn't work for any of my students. It's hard enough to get the ball to float above the straw for any length of time! So I have to say that, although that was probably their favorite of all the experiments, to me it was the least useful.

Still air is strong air. And if you have them say that over and over -- and make muscles and do body builder postures and grunt -- it really sticks! They joked that I could have a shirt made up that says STILL AIR IS STRONG AIR and wear it when we go to the Science Center. My Bernoulli swag!

FUN FACT: While in Venice, a seafaring city, Bernoulli learned the Paris Academy was offering a generous prize for the best design of a sand-clock for timekeeping at sea. His response was to design an hour glass whose trickle of sand was unaffected by rough seas. For this work he was awarded the Grand Prize. (from https://www.famousscientists.org/daniel-bernoulli/)

Wednesday, Dec 7

recall last week's lesson

do final experiment from Bernoulli Brain-Teasers (PDF)
cookie sheet, pencils, tape, plastic wrap, sink or tub, soapy water

we did this in three teams of three children

we did this outside on the driveway (which is on a slope)

each team needs a large (11 x 17") cookie sheet, a handful of old pencils, and a roll of cellophane tape



be advised that they will use A LOT of tape

I came around and tore a piece of plastic wrap for each group

after they set up their channels I had them sketch a diagram of their setup before they could get their soapy water (a large red plastic cup, water, dish detergent, plastic knife to stir)

after they poured the water they added notes to their diagram as to what happened

This experiment has a huge cleanup because there will be plastic wrap and little pieces of tape everywhere, and a bunch of wet and very soapy pencils to try to clean and dry off, so I suggest having a trashcan and a roll of paper towels handy. It did work well to do it outside. It did NOT work well to help them understand Bernoulli's principles. They all thought that the water slowed down when it went through the narrow passageway. So I would NOT recommend this experiment.

do Density of a Candy Bar Lab ($2.80 on TpT)

Again, we worked in three teams of three students but I do think this one would be better in pairs. In the soapy water lab there were more jobs for people to do, so group of 3 were fine. But in this lab, I saw some people sitting around with nothing to do, especially when the calculating happened at the end. And you could divide up the measuring very simply (one person does length/width/height and the other person does mass). And it's easy to divide up the chocolate bar at the end.

I printed only page 3 of the PDF, so that they had a data table

Each team will need a paper plate, Hershey's chocolate bar (or vegan alternative), and a ruler.

I had them share the kitchen scale. They had to measure in centimeters and grams.

Before the exercise, we had a discussion about what density is. We remembered the ocean bottle (oil and water) and how the oil will always move to the top, no matter if you shake it hard, no matter if you flip it upside down. We thought about the difference between mass and volume. We brainstormed how two things could be the same mass but one could float and one could sink. What are some things that could have a mass of 10 grams but sink? What are some things that could have a mass of 10 grams but float? What do the sinking things have in common? What do the floating things have in common? Could you take a sinking thing and change it into a floating thing by keeping it the same material but changing its shape? This is something to explore next time!!!!

Density is the relationship between mass and volume.

They did all of the measurements for their whole and half candy bars and wrote them in the chart. Then we came back together. Give EACH TEAM a calculator for the next part.

I asked them, if volume is how much space you take up (and I stretched my arms up high), to represent this would you use the length? width? height? or all three? They said, all three. So I told them to multiply the l x w x h and write the result in the righthand margin of their worksheet. We drew a heavy vertical line after the mass column in the data table to make this distinction easier to see.

Then I reminded them that density is the relationship between mass and volume. And the way that you can express that relationship in a single number is to divide mass by volume.

D = m ÷ v

So they calculated that and wrote the answer in the lefthand margin of their worksheet. Then we discussed everyone's answers.

The team that is most careful with their measurements will of course get the best result.

They were very surprised that the density was the same for both (even the people who had predicted that it would be the same... which makes me wonder why they had checked that prediction). But then we talked about how it's like equivalent fractions. You have a relationship of 1/2. You multiply the top and bottom by 3 and you get 3/6 but those two numbers still have the relationship of 1/2. If you have chocolate (which has a certain density, ie. a relationship between mass and volume) and you cut the mass in half and the volume in half, those two new numbers will still have the same relationship.

Density is changed only by a change in temperature or pressure.

I really liked this lab because it involved practicing measuring with a ruler (a skill kids don't use that much in real life, so they get very fuzzy on it quickly) and making calculations. I would definitely do this again! I let them eat the chocolate afterwards. I gave everyone a whole chocolate bar because I was in a hurry (I recommend that you allot less time for the measuring than you think but more time for the calculating than you think) but upon reflection it would of course have been better to give everyone half. A whole 1.55 oz bar is a lot of chocolate. And if I had organized the children in teams of two, they could have just each eaten half the bar.

Wednesday, Jan 4

review the science content we have covered so far by reading chapter 1, "The Air Around You," of The First Book of Weather by Rose Wyler


The First Book of Weather
by Rose Wyler

stopping for discussion, acting things out, and notetaking as follows:

p.2 - add Fun Fact to Science Club notebook
two million air molecules placed in line would hardly stretch across a grain of salt

p.3 - act out being the Earth's gravity pulling on air molecules and likening it to a greedy trick-or-treater grabbing and grabbing at candy until he has a huge pile of it all around him

p.4 - add illustration to Science Club notebook
gravity holds down the atmosphere

p.4 - add Fun Fact to Science Club notebook
nine-tenths of the air molecules are in the first 10 miles above sea level

p.4 - make a line of childen as air molecules standing close together, bumping into one another, and passing the movement along; then have the children scatter all around the living room so that they cannot reach each other (just as in the high levels of the atmosphere, where wind cannot exist)

p.5 - use the first joint of your thumb to approximate an inch and imagine a square inch of ground

p.5 - add Fun Fact to Science Club notebook
the total weight of all the earth's air is over 5 quadrillion tons

p.5 - add illustration to Science Club notebook
the tall column of air above you pressing down on you (our bodies are adapted to this, as deep sea fish adapt to the pressure in which they live... when a blobfish comes out of the ocean his body cannot withstand the rapid pressure change)

Blobfish might be a gooey mess out of water, but check out a living one! (VIDEO)


Pink Is For Blobfish: Discovering the World's Perfectly Pink Animals
by Jess Keating

pp.6-7 - we did not read about this experiment; instead I opened a can of vacuum-packed coffee (Eric Sloane writes on page 24 of his book, "Of course, the vaccuum is not a complete one, but the pressure inside the can is simply less than the pressure outside; when you open the can you can hear the outside atmosphere rush in with a pfuff sound.")



p.9 - act out being the Earth both rotating (Fred the rooster makes one complete circuit in 24 hours) and revolving around the Sun (Fred makes one complete circuit in 365 days)

p.14 - add illustration to Science Club notebook
the top of mountains are cold because the air is warmed from below by the earth (the sun's rays warm the earth and then the earth gives off heat into the air)

p.18 - look at chart on p.25 of Eric Sloane's Weather Book

before reading page 19, look at, act out, and thoroughly explain the eardrum diagram on p.26 of Sloane's book

the membrane on the top of the unopened coffee can will act exactly like the eardrum, and strech out or push in in response to the changing air pressure (there is another variation/ illustration of this experiment on p.24 of Sloane's book)

because the coffee can is completely sealed and has no "Eustacean tube" escape valve to help it adjust and equalize the pressure, it has no choice but to respond to the change

before reading page 21, show illustration on p.25 of Sloane's book

do coffee can barometer experiment on p.19 of Wyler's book

record the current needle position on barometer in Science Club notebook

watch Pressure Demo: Balloon and Shaving Cream

Wednesday, Jan 11

read page 25 of Sloane's book, choose a new location for our barometer so that it is away from a door and away from a heater

review answers to Science Club Quiz, add a more complete explanation of how a thermometer works to Science Club notebook

break into two teams

team 1 - temperature - Drawing Isotherms (pages 1, 3 & 4 of PDF)

team 2 - air pressure - Graphing Pressure (page 2 of PDF)

we only graphed air pressure

cut piece of graph paper in half and tape it to itself so that it is long and thin, label the altitude axis correctly without a break

x axis - air pressure - measured in millibars
1 square equals 100 mb
this axis should go from zero to 1200 mb

y axis - altitude - measured in kilometers
1 square equals 10 km
this axis should go from zero to 500 km

come back together and share your activity with the other team

our previous exploration: temperature

our next exploration: wind direction

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