Conservation of Matter: Steel Wool & Vinegar

This is another versatile demonstration to use in your student of chemistry - learn about chemical changes, chemical reactions, conservation of matter and even air pressure.

Depending upon the take-home message you want your students to get, you might structure the activity in a few different ways, but the basics are the same.

You'll need some steel wool, vinegar, bottles or flasks and a balloon.

Pull apart some strands of steel wool and push some into each bottle.  Pour some vinegar onto the steel wool.  (Some instructions tell you to soak the steel wool in the vinegar for a few minutes and then remove the steel wool.  I just left mine in it).

Stretch a balloon over the opening of one bottle, but leave the other as is.

You could find the mass of each system at this point, if you're interested in conservation of matter.

Allow the bottles to sit and the reaction to occur. 

The vinegar removes the coating from the steel wool, and the steel will be begin to oxidize in the presence of oxygen. 

As the reaction is occurring, the balloon will be pushed into the bottle.  Why?

The oxidation reaction is using up the oxygen in the bottle, which will lesson the number of air molecules in the bottle, thus reducing the pressure in the bottle.  Because the pressure outside the bottle is greater than the pressure inside the bottle, it will push the balloon in. 

You can stop there if you're interested in simply looking for evidence of a chemical change, studying the chemical reaction or seeing the affects of air pressure. 

If you're interested in conservation of matter, continue on. 

Find the mass of each system once again.

The closed system (i.e. the one with the balloon covering the opening), should have the same mass it had in the beginning. 

The open system's mass should have gained mass, as it continued to pull more oxygen into the system to carry out the reaction further. 

Air Pressure: Egg into a Flask

This is another classic! 

In preparation for this demonstration, you'll need to hard boil some eggs.  When cool, peel them. 

You'll need a flask or bottle (Snapple bottles are a good size) with an opening that's smaller than the egg (the egg should be able to sit on top of the opening.  You may wish to grease the opening a little to help the process, but it usually isn't necessary.

To perform the demonstration:

Light a small piece of paper on fire with a match or lighter.  Drop the paper into the flask/bottle.  Quickly place the egg on the opening.  Watch.

The fire will extinguish when all the oxygen has been consumed.  And the egg will slowly work its way into the bottle/flask.

Since the oxygen has been consumed, there is less air in the flask, so the air pressure outside of the flask pushes the egg in. 

(At this point, you're probably looking for an additional picture.  My camera went on hiatus, so there is no picture, but I can tell you that my egg was too large for the bottle I had on hand, so even if I had a picture, it wouldn't look terribly different from the one above.)

There are ways to use air pressure to get the egg out, but I can never get them to work.  Instead, I break up the egg with a knife and dump it out.  Not as dramatic, but it works!  If you're interested in trying it for yourself, do a Google search and you'll find numerous sites with directions.

You'll probably want to try this demonstration once before performing, to check that your bottle/flask opening and egg are a good size match.  (See above).  Of course, eggs are all slightly different sizes, so there's no guarantee that you won't get the egg stuck in the neck of the flask, but it should give you a good idea!

Flatten an Index Card

Challenge your students (or family members or friends or anyone else you encounter) to find two ways to flatten an index card, without touching it.

To prepare, fold an index card in half and set it on the table to make a tent. 

Your challengee will likely immediately blow on the top of the card to push the middle down.

The challenge comes in finding a second way to accomplish the task. 

It's time to put your knowledge of Bernoulli and air pressure to work!  By blowing under the card, you'll move those air molecules out of the way, allowing the air molecules on top of the card to push the card down.

Air Pressure and Bernoulli:Clanging Cans

This demonstration is very similar to the balloons and the cardboard tubes.

There are two ways to try this one:

Version 1:
First, lay two empty soda cans on their sides a few inches apart, parallel to one another.

Blow between the cans and watch them roll together.  It happens because you've pushed the air molecules that were between the cans out of the way, so the air pushing on the opposite sides of the cans is unbalanced and the roll together.

Version 2:
Set up a bunch of straight straws parallel to one another, about half an inch apart from one another. 

Set the two cans upright on the straws, a few inches apart.

Blow between the cans and watch!

Summer Science Camp: Air Pressure Demonstrations

If your budget or location doesn't provide you with the opportunity to do a Chemistry Magic Show, consider a series of air pressure demonstrations.  They can be just as much fun, and the science behind them is easier for younger students to understand than the chemistry. 

Start things with a bang - literally - and use air pressure to crush a can. 

It follows nicely to collapse a milk jug. 

Set up the Balloon in a Flask and have students keep an eye on that while you're proceeding through other demonstrations. 

Sucking an egg into a flask is always a favorite.  A simple Internet search will provide you with instructions thousands of times over. 

Challenge a student to Blow up a Balloon in a Bottle! 

Give your students a shower with the Straw Fountain. 

Find two strong students to try to pull apart Two Plungers. 

Bernoulli demonstrations are a bit counter-intuitive and fun.  Try the cardboard tubes or balloons. 
And, if at all possible, finish with some bell jar demonstrations.

Air Pressure: Plungers!

On a large scale:

Get your hands on two plungers - new and clean would be preferable (I've actually seen small ones, perfect for this demonstration, at a dollar store)! 

Match up the edges and push the plungers together.

Now try to get them apart.  Not an easy task! 

You pushed all the air out of the middle, so there's nothing pushing them apart.  Only lots of air on the outside pushing them together.

In the end, if you have a good seal, you'll need to force some air in to break the seal, but splitting the plungers apart.

On a smaller scale:
You can have your students perform this activity themselves using suction cups (the kind you sometimes use to hang things in your windows).  The physics is exactly the same, just smaller!

Air Pressure and Bernoulli: Rising Paper

This simple activity is a great introduction to Bernoulli. 

Cut strips of paper, about 1 cm wide.

Hold a single strip up to your lip. 

What do you think will happen if you blow across the paper?  How will the paper move? 

Many students will think that blowing across the paper will push it down.  In fact, just the opposite happens:

By blowing, you push the air molecules above the paper out of the way, so the air molecules located below the paper are unbalanced and push the paper up. 

Weather: How Much Air is Pushing on You?

The air all around you is filled with molecules, all of which exert pressure on you. 

Picture this...
You're standing upright.  Rising straight up from your head, into the furthest reaches of the atmosphere, is a column.  This column is filled with air molecules.  While the effect of each individual molecule is miniscule, their combined effect is a force with which to be reckoned.  How much atmospheric weight do you think your head has to support?  Go ahead, take a guess...

First we need to find out how large your head is.  For the purposes of this activity, we're going use inches so we can get an answer in pounds.  It's rather un-scientific of us, but it will provide us (in the U.S.) with the greatest understanding.

Back to your head.... find the circumference of your head, using either a fabric measuring tape or a length of string that you then lay against a meter stick.  I come up with 22 inches.

Now you'll need to do some math to find the radius.  Circumference is equal to 2 x pi x radius.  So, to get the radius, you'll need to divide the circumference by pi and then divide that number by 2.  For me, it's 3.5 inches.

Now you'll use the radius to find the area of the top of your head.  Area is equal to pi x radius x radius.  For me it's 38.47 square inches. 

Atmospheric pressure at sea level is 14.7 psi (that's pounds per square inch), and while I don't live exactly at sea level, that number will work well enough for our purposes.  So, the area of my head multiplied by atmospheric pressure gives me the weight of air pushing on my head.  In my case, it's 38.47 square inches x 14.7 psi = 565 pounds. 

Pretty unbelievable, isn't it?  But it's true.  We aren't aware of it because we're used to it, we've never known anything different.  And we aren't crushed by that force because there are fluids inside our body exerting pressure that keeps things balanced.  Those air molecules are pushing on all sides of your body, not just on top of your head, which also helps keep things balanced.

If you're interested, atmospheric pressure in Denver, with an approximate altitude of 1 mile, is 12.2 psi.  You might want to have your students determine how much the atmospheric weight changes as they go from sea level to 1 mile.

Air Pressure: Suction Cup Drink Holder

Education Innovations sells these neat rings that work like a suction cup to hold your drink. 

You slide a can or bottle into the ring, set it on a smooth, flat surface and it sticks! 

While not terribly expensive, it's simple enough to make your own version.  You'll need a flexible, stretchy material.  I've found that the plastic jar grippers, sometimes given away by companies, work well.

The original Lil' Suctioner has a radius of just over 2 inches.  While I wouldn't go smaller than that, it certainly wouldn't hurt if yours was bigger. 

Cut about a one inch hole in the center of your material. 

Slip the material over a can or bottle and test it out for yourself. 

By the way, the Lil' Suctioner includes some air pressure facts, including the weight of the atmosphere pushing down on it (~221 lbs).  But, there's no reason you can't figure it out for your own drink holder.  If it's a circle, measure the radius; if it's a rectangle, measure the length of the sides.  Make all measurements in inches. 

Calculate the area of your material (for a circle: pi x radius x radius; for a rectangle: side x side) and multiply that area by 14.7 psi (pounds per square inch).  That will give you the number of pounds of the atmosphere pushing down on your drink holder, of in other words, the pounds of force you'll have to exert to lift up your drink.

Air Pressure: Penny in a Balloon

Place a penny inside an uninflated balloon.

Blow up the balloon, most but not all the way.  Tie the balloon.

Dip a pin or needle in some cooking oil.  Poke the pin into the balloon, into the end opposite the knot.  Remove the pin.

Hold the knot and twirl the balloon around, so the penny goes to the bottom.  Have the penny cover the hole made by the pin.

Turn the balloon over and observe the penny - it "sticks" to the top of the balloon. 

By inflating the balloon, you increased the air pressure.  The force of those air molecules is greater than the force of gravity, so the penny stays where it is.  (It doesn't take much of a force from your finger to overcome the force of those air molecules!)

Bernoulli: Ball in a Cup

Challenge your students to get the ping pong ball out of the cup* following this 1 rule:
     ~~They cannot touch the cup or ball with any part of their body.~~

The only way I know of to complete this task is to apply Bernoulli's Principle by blowing across the top of the cup and ball, allowing the ball to rise.

If that's too easy, you can add a second step to the challenge and have the students move the ball from one cup to another without touching anything.


*Try out the cup you plan to use ahead of time.  If the cup is too deep, it won't work.  If you use a paper cup, you can always cut the sides down.  But, be careful, if the cup is too shallow, students will just blow the ball out and not put Bernoulli to use.  I found that a cordial glass (see below for a cordial glass story) works well, if you have one shaped like mine!


Here's the story... when we were little (like, before we started school), my cousins, brother and I drank apple juice out of mini wine glasses at my Grandma's on special occasions, like Easter.  I was in college before I realized that those glasses were not in fact miniature wine glasses made for small children to use when the grown ups were drinking wine, but were really cordial glasses.  :)  Who knew?!?!

Air Pressure: Dry Paper

Fill a tub or small aquarium with water (the water should be deeper than the cup you're planning to use for this activity).

Crumple up a sheet of paper and place it in the bottom of a cup (use enough paper so it will stay in the bottom when the cup is turned over.

Hold the cup upside down and push it into the water.

Pull the cup up and out of the water.  Remove the paper.  Is it wet or dry?  Why?

The cup was filled with air.  When you pushed the cup into the water, you trapped the air in the cup.  The air pushed on the water, pushing it out of the way of the cup.  As a result, the paper stayed dry.

Air Pressure: Bell Jar Demonstrations

If your school has a bell jar and vacuum pump, break them out!  Try some of my favorites:

- 1 -
Fill a small beaker part way with water.  Have some students touch the water - it's cool/room temperature.  Place the water in the jar and turn on the pump... the water quickly boils.  Remove the water and have students touch it again - it's still cool/room temperature!  With no air pressure, water boils at room temperature! 

 - 2 -
Fill a small balloon with just a small amount of air (just enough so there's air in there, not enough to even stretch the balloon).  Place the balloon in the jar and turn on the pump.  The balloon will expand!  Without air surrounding it, the air molecules trapped in the balloon will begin to expand, thus expanding the balloon!

 - 3 -
Place a marshmallow in the jar and turn on the pump.  The marshmallow will grow right before your eyes!  It's like the balloon above - there's air trapped in the marshmallow that expands when outside air pressure is removed.  Eventually the sugar structure will be stretched to its breaking point and the marshmallow will stop expanding.  When you return the air pressure, the marshmallow will be completely crushed - there's no structure to support/trap air molecules any more.

For some extra fun, pick up some extra Marshmallow Peeps during the holidays!

 - 4 -
Place a small dollop of shaving cream in a small beaker.  Set the beaker in the jar and turn on the pump.  The shaving cream will expand, out of the beaker and will fill the whole bell jar (be careful - turn off the pump before the shaving cream gets into the pump - that would be disastrous).  The shaving cream has air trapped inside of it.  It behands in the same manner as the marshmallow. 

You can also use whipped cream for this, but I find ath shaving cream cleans up very quickly and easily. 

**I've been told that you can do the marshmallow "trick" in one of the vacuum systems for food preservation (the kind that pulls the air out of a jar).  Not having such a system, I haven't been able to confirm, but that information came from a very reliable student.

Air Pressure and Bernoulli: Balloons!

Hang two balloons so they are a few inches from one another.

Blow through the gap in the middle of the balloons.

The balloons move together!  You pushed the air molecules from the middle out of the way, allowing the air on the other side of the balloons to push them toward the middle.

Air Pressure and Bernoulli: Cardboard Tubes

Place two cardboard tubes (make sure they're nice and round) on a table, an inch or two apart from each other.

Use a straw to blow through the gap between the tubes.

The tubes roll together! You pushed the air molecules from the middle out of the way, allowing the air on the other side of the tubes to push them toward the middle.