## Magdeburg Vacuum Plates

April 1, 2013

by: Jon Smith

Teaching the basic concepts of air pressure has always been one of my favorite units in Physical Science.  There are so many great demonstrations, some with long colorful histories.  One classic standby is the use of the famed Magdeburg Hemispheres.  The Magdeburg Hemisphere demonstration was invented in 1656 by Otto von Guericke, then mayor of Magdeburg, Germany.

Having just invented the world’s first vacuum pump, Von Guericke set to work creating a device to demonstrate its valuable contribution to science.  That device was the Magdeburg Hemispheres.  Von Guericke’s original spheres were much larger than those commonly available today and made of thick metal.  He used them to dramatically demonstrate the pressure of the atmosphere by evacuating them and using two teams of 15 horses to attempt and pull them apart.  Of course the horses failed to separate them.

Most spheres commonly sold today are made of cheap black plastic and meant to be evacuated with a typical classroom vacuum pump.  They do a reasonable job of demonstrating the basic concept, but, in my own experience, do not hold up well to normal classroom use.  Over the span of my 20 year career I have probably had to replace these hemispheres at least five times.

When Educational Innovations began selling their Magdeburg Vacuum Plates, I thought that I would give them a try.  I was incredibly impressed!

While the plates lack the traditional hemispheric shape, what is gained from the shape change is significant.

By changing the area exposed to atmospheric pressure to a two dimensional circular surface, my 9th graders had no problem calculating the exact amount of pressure holding the plates together.  In addition, because the plates are two dimensional it allowed the designer to provide three different sized grooves and “O”-rings to actually change this area.  When the area is decreased, the force that holds the plates together is also decreased.  Not only can my students do the calculations to determine the new areas and corresponding forces, but they can “feel” them as well.  Using the largest groove and “O”-ring creates an area that requires roughly 170 lbs of force to separate.  Using the smallest “O”-ring, it only takes little over 60 lbs.

The product also comes with a very nice manual with a suggestion that I had never thought of.  Once I have my students calculate the force required for a given area, I have one student stand on a bathroom scale holding the upper handle of the evacuated plates while another student sits on the floor in front of the first student and pulls downward on the lower handle.  The students then watch the scale and note the maximum weight it records before the plates separate.  This weight, subtracted from the student’s weight, roughly approximates their calculated force.

I particularly like the fact that the vacuum plates come with their own hand pump.  While I own both a classic large laboratory electrical vacuum pump and a smaller “squeeze-type” pump, I love the fact that the included pump has an obvious mechanism that students can see.  The creation of the vacuum between the plates becomes something transparent and understandable rather than a magic “black box.”   This same pumping system is used in Educational Innovations’ mini-bell jars, and I love those, too.

Finally, I am most impressed with the strength and durability of these plates.  My set has been dropped, kicked, and beaten in every way imaginable by 9th graders over the past 5 years, and they still work like they did the day I took them out of the box.  I used to guard my Magdeburg Hemispheres protectively.  Now I pass these plates around the room and just let my students “have at them.”  It’s nice to have the kind of durability that turns a quick “one-off” demo into a truly “hands-on” experience.  Thank you EI!

## Look, Mom, No Wheels!

February 25, 2013

by:  Norm Barstow

The first practical design of the hovercraft was completed in the late 1950′s by British engineer, Sir Christopher Cockerell.  Since then, the continued development of this invention has been ongoing, and currently, the hovercraft is being used commercially, by the military, and for personal use.  Teachers have been constructing versions of the hovercraft using balloons, film canisters and flat materials in classrooms for years.

The principle behind the hovercraft’s levitation is that when the air is released from the balloon, it hits the ground and rushes outward in all directions. The air flowing from the balloon through the holes forms a layer of air between the hovercraft and the table. This reduces the friction (the resistance that occurs when two object rub against each other) that would have existed if the hovercraft rested directly on the table. With less friction, your hovercraft scoots across the table.

Furthermore, extra air molecules are packed underneath the structure, which in turn increases the pressure under the hovercraft.  This increased pressure below the craft produces an overall upward pressure force on the craft therefore it supports its weight. Since air molecules are always leaking out from beneath the craft, you’ll need a source of air molecules to replace them, which is provided by the balloon.

### Materials:

·      Large plastic plate (not the inflexible type)
·      Foam meat tray from grocery store  (6.5” X 8.5”)
·      Old CD
·      Stiff cardboard

• Poster putty such as Blue Tak, or Poster Tak
• Smooth surface
• Hole instrument: Ball point pen tip or hot nail or drill.

### Construction of the hovercraft:

1.  Find the center of your base and make a hole (3/32” or about the size of  the hole in a spool of thread.)  Caution.  If you use the plastic plate, it is best to use a hot nail because a ballpoint pen tip will not make a round hole.  Use vise grips to hold the nail and heat it over a flame.

2.  Make a similarly sized hole in the bottom of the film canister. You can use a ball point pen here or a hot nail.

3.  Stretch the balloon and fit the opening over the open end of the film canister.  Be sure to fit the balloon far enough onto the film canister so the neck of the balloon keeps the inflated balloon upright and does not flop over.

4.  Make a ring of the Poster Tak around the hole in the base. Be sure not to cover the hole.  The ring should be the diameter of the film canister base.

5.  Inflate the balloon by blowing through the hole in the bottom of the film canister. When it is fully inflated, have a partner pinch the neck of the balloon or twist it so it doesn’t deflate.

6.  Carefully set the balloon/film canister assembly on the ring of poster putty and press down to seal.

7.  Place the Hovercraft on a smooth surface and let the air flow.

8.  Give it a little tap to get it going.

Here is a step by step video to help you get going:

### HINTS and SUGGESTIONS:

• Place a piece of tape over the base of the hovercraft until you’re ready to launch.
• Experiment with inflating the balloon, twisting it to seal in the air, and then trying to fit the balloon neck over the film canister opening.
• Experiment with different hole sizes, bases, balloon sizes.

## Bernoulli’s Principle: Lessons Made Out of Thin Air

November 25, 2012

by:  Tami O’Connor

A few weeks ago my daughter, a new fifth grade teacher, asked me to come into her school to present a hands-on science lesson.  Nothing delights me more than working with kids in a classroom.  After 16 years of teaching, it’s hard to be away from it.  At first I was unsure what I was going to bring in.  I have so many really neat activities at my disposal that it is difficult to select just one.  I finally narrowed it down to activities dealing with air pressure, which is part of their curriculum (always a plus!).

As I rummaged through the office, I unearthed my supply of funnels, flex straws, and ping pong balls and decided that Daniel Bernoulli would be my guest of honor that day.  When I started my lesson, I blew up a balloon and talked about air and its properties.  Inviting comments, I discovered that they had some very interesting background knowledge, and most of it was correct…

I then pulled out another balloon, only longer and made from plastic rather than latex.  It was actually a windtube; our eight foot long Bernoulli bag!  My first question was, how many breaths would take to inflate the wind tube?  Guesses ranged from 50 to one million.  It was, after all, a group of ten year olds…  I bunched the end and brought the bag to my mouth.  I decided to put just 5 breaths into the bag, and then after pushing all the air down to the bottom of the windtube, we estimated how many additional breaths it would take to completely fill the bag.  As it turned out, had I filled the bag the same way I started, it have would taken about 45 of my deep breaths to inflate it fully.

At this point I threw out a challenge: if anyone in the classroom could inflate the bag using their breath faster than I could I would give the entire class the rest of the day off to play outside.  Well, as you can imagine, the kids began to assemble their “dream team”.  I explained they could only select one person as my opponent.  They put forth the captain of the swim team explaining that his lung capacity was better developed than any of his classmates.  We stood back to back, and we each had a teammate holding the far end of our windtube so the spectators could track our progress.  One student in the class was selected to announce, on your mark, get set, and GO!  At that point I started faking the sound I would make if I were actually trying to inflate the bag, to fool my opponent into thinking I was working really hard.  After he had put about 6 breaths into his bag, I stood back and held my bag at arm’s length with the mouth of the tube wide open and blew a long steady stream of air into the opening of the bag.  Within seconds the entire tube was filled.  At this point all the kids in class began to giggle since the swim captain was turning red and still working relentlessly to inflate his bag.

Why did this happen?  According to Bernoulli, a fast moving column of air creates a decrease in air pressure.  Only a small percentage of the air in the bag came from my lungs.  The rest was drawn from the room.  As I increased the speed of the air I directed into the opening of the windtube, the pressure around it decreased and more air was drawn into the bag.

Ok, so now the class totally understood the concept, and it was time for the next activity.  I gave each student a flex straw, a funnel, and some clear tape.  They were instructed to attach the narrow end of the funnel to the short end of the straw using the tape.  I assured them that the funnel and straw did not need to fit snugly.  The tape connected the two pieces kept any air from escaping.

I asked the students to place their hand above the opening in the funnel, blow into the straw, and tell me what they felt.  As expected, the kids felt their breath exiting through the wide end of the funnel.

Now, with their new-found knowledge of how fast moving air creates low pressure, I asked the students to predict what would happen if they put a ping pong ball into the opening of their funnel and then blew into the straw.  Each and every one of them predicted that the ball would be blown out of the funnel!  Some even went so far as to boast that their ping pong ball would hit the ceiling (of course they stipulated that they had to be standing rather than sitting at their desks). Many times in my teaching career I wished I had brought a camera into my classroom.  That day was one of them!  When I counted to three, every face in the room turned red while they tried with all their might to blow that ping pong ball out of the funnel.

Of course, the ping pong ball wasn’t going anywhere.  Bernoulli’s Theorem, also known as Bernoulli’s Principle, states that an increase in the speed of moving air (or any flowing fluid) is accompanied by a decrease in the air or fluid’s pressure.  The airflow around a ball or other curved object placed in an airstream will increase its speed.  When the air increases its speed its pressure decreases.  The low air pressure created around the ball allows the high pressure from above the ball to push the ball back into the funnel.

Ok, so after the students were able to explain this concept to me we moved onto the next activity.  Using the same straw, I gave them each two pieces of 1.5”x1.5” oak tag and a toothpick.  One piece of oak tag was hole punched in the middle, and I instructed the students to attach the card to the short end of the straw so that the hole was flush with the end of the straw and it looked like a tabletop. I asked them to secure the bottom of the card to the straw using tape.

Next, I pushed a toothpick through the center of the second card and placed the two cards together with the toothpick protruding into the straw.  The next challenge…  What would happen when I blew through the straw?   Surely, after the last two demonstrations they would get this one.  Only one lone student hypothesized that the cards would remain together.  The others insisted that the cards would fly apart, but because of the toothpick the second card would fly straight up.  How I wanted to cringe.

Needless to say, the class (well, all but one) was amazed that no matter how hard they exhaled into the straw, the cards remained together.  The only thing that was even more impressive was when I instructed the class to rotate their straws 180 degrees, while holding the second card in place, and to blow.  As they blew a steady stream of air into their straws I had them remove their hands.  Then the excitement became even more apparent as the cards still remained together!  Well, at least until they stopped blowing to try to get my attention.  By this point the kids were all able to explain that the card remained in place, defying gravity, because the decreased air pressure between the cards allowed the higher air pressure from within the room to force the cards together.

The final activity involved the straw, two ping pong balls, a 12-inch piece of kite string and some tape.  Working in pairs, the students attached one ping pong ball to each side of the string with tape.  While one student held the string with the ping pong balls hanging approximately 1 cm apart, the second student blew a steady stream of air between the two.  As they had predicted, rather than moving apart, because of Bernoulli’s Principle, the spheres actually moved together!  Phew!  Though it took a little while, the concept was finally clear in their minds.  A fast moving column of air creates a low-pressure area and draws other objects in.

As I left the classroom, the students were trying to come up with other ways to demonstrate how Bernoulli’s principle could be demonstrated.  It just doesn’t get better than that!  Once I returned to the office, I realized that, though all the materials are fairly common, they not always found together.  So I put a kit together, and we now produce it at EI.  Bernoulli’s Principle Class Kit has all the materials you will need to conduct the activities mentioned above with a class of 25 students.

## Bubble Basics

November 12, 2010

by: Michelle Bertke and Melanie Bunda

Bubbles are always a fun and interesting activity for kids of all ages.  However, bubbles are not only fun, they are also an excellent teaching tool for some abstract concepts such as air density, dissolved gasses, and air pressure.  Below is a collection of bubbly activities that highlight each of these topics. Educational Innovations offers a full line of wonderful bubble products!

Gravity Defying Bubbles

Different gasses have different densities.  The air around us is mostly nitrogen (N2) and oxygen (O2), which are both lighter than carbon dioxide (CO2).  When a heavy gas, such as CO2 is placed in a tank, it will sink to the bottom without mixing.  This can be achieved by placing a few blocks of dry ice in a large fish tank or clear plastic bin covered loosely with a lid and allowing them to sublime.  This will take several minutes. Always use caution when handling dry ice by using proper gloves and safety goggles. Once full, blow bubbles over the surface of the tank.  When the bubbles reach the interface of the two gasses, they will float.  If you fill the tank with CO2 unnoticed, have the kids speculate as to why they think the bubbles didn’t reach the bottom, and what might be in the tank.  An alternative is to fill a balloon with CO2 by filling it with baking soda (or an alka seltzer tablet) and placing it over the opening of a bottle filled with vinegar (or water).  Lift the balloon so the contents spill into the bottle and react with the liquid, allow the balloon to fill from the reaction, twist and remove.  Use it to blow bubbles.  Compare these bubbles to those blown with regular air (use a fan, not your breath for best results).  Have students compare the two bubbles.  Which one falls faster? Which one floats longer?

Dancing Raisins

All kids will know that soda pop is fizzy, but they may not know where all those little bubbles come from.  This demonstration will highlight the dissolved gasses in soda.  Fill a glass with a clear soda.  As you pour in the soda (pour gently down the side to retain maximum fizziness in the liquid), you will see bubbles forming from the bottom and the sides of the glass.  Ask the students why they think that bubbles only form in these places.  Next, take a few raisins and drop them into the soda (you may need to break the raisins into smaller pieces).  You will notice that bubbles immediately begin to form in the crevices of the raisins.  As more bubbles collect on a raisin, it will begin to rise.  When it reaches the top, the bubbles on the outside will escape into the air and this will cause the raisins to sink, and the cycle to begin again.  Pretty soon you will have a glass of dancing raisins.  This should raise discussion about dissolved gasses and buoyancy.  Students can experiment with different sodas and different materials to see what may cause more or less bubbles to come out of solution.

Mentos and Soda

Another classic example of dissolved gasses is the Mentos and soda demonstration.  This demonstration can be done by anyone with just a two liter bottle of soda and a pack of original Mentos.  Make sure you are in an area which can get messy and sticky.  Simply open the soda and the pack of Mentos.  (Fashion a Mentos delivery apparatus out of a rolled up piece of paper to prevent getting sprayed.)  Quickly drop the Mentos into the soda all at once and immediately step back.  The ensuing fountain will go high into the air and cause widespread excitement.  The same tests can be done as were mentioned in the raisins: what kind of soda makes the highest fountain? Do different types of Mentos cause differences in the height of the fountain?

Square Bubbles

All bubbles are round.  Or are they?  A free flying bubble, no matter what shape wand produced it, will always be round.  Why is this?  When you blow a bubble, the soap solution stretches as the air flows into it, and the air pushes equally on all sides of the bubble.  This creates a perfectly spherical bubble with equal pressure on all sides.  But what happens when the wand is a three dimensional cube?  Make a cube frame out of pipe cleaners.  (Make sure to attach a handle to hold on to.)  Fill a tall beaker with soap solution and dip the cube into it, fully submerging it.  Remove the cube from the container, and you will see a square “bubble” stretched between the sides of the form.   If you blow on one side of the cube structure, the sides will collapse in on each other and come together at a point.  Now take a straw and gently blow into the center of that point.  If you get it just right, you can form a cubic bubble in a bubble!  Give the students several pipe cleaners and allow them to create their own 3D bubble wands.  See what other kinds of bubbles they can form.

Any way you look at it, either from a scientific point of view or as a kid on a sunny day, bubbles are a fascinating activity to be shared by all.  Next time you are strapped for something to do, just whip up a batch of bubble solution and let your imagination run wild.

## Science Never Sucks

May 27, 2010

by: Tami O’Connor

One of my all time favorite air pressure activities is an oldie and a goodie!  It involves getting an egg into a classic, hard-to-find milk bottle, like the ones delivered to grandma’s door.  Unfortunately, some students (and some teachers) still think an egg can actually be sucked into a bottle.  As you probably know because the air pressure is greater outside of the bottle than inside, the better explanation is that the egg is literally pushed into the milk bottle.

Here is the explanation… The demo begins by placing two or three burning matches or a burning strip of paper into the empty bottle.  Then a shelled, moistened hard-boiled egg is placed on the mouth of the bottle.  The egg is clearly larger than the opening in the bottle.  The air inside the bottle begins to heat up and subsequently expands.  It is easy to notice the egg dancing around a bit as the air inside the bottle escapes around it.

Shortly after the flame inside the bottle extinguishes, the egg enters the bottle with a noticeable pop!  There is no doubt that the kids just love this demonstration.  I’ve done it at a number of science demonstrations and assemblies, as well as in my own classroom, and the response is always a surprised gasp followed by applause!

The only thing the kids enjoy more than watching the egg enter the bottle is watching me trying to get the egg back out of the bottle…  In my younger days I learned that I could only do that demo once since I had to wait to get the kids out of my class before I would attempt to blow the egg out of the bottle.  I’ve had egg on my face more than once…  The trick is, after blowing into the mouth of the inverted bottle, moving your face away quickly… well, very quickly.

As I got more creative (and spoke with more experienced teachers), I realized that there are other ways of getting the egg out of the bottle besides blowing into the mouth.  Another way to accomplish the same results (while remaining clean!) is to pour hot water on the outside of the bottle while the egg is seated the neck of the inverted bottle.  I usually rinse the inside of the bottle out with cold water first.  The process of running hot water over the outside of the bottle filled with cool air serves to warm the bottle, thus warming the air inside the bottle and causing the air to expand once again, forcing the egg out of the bottle.  Blowing a hair dryer over the outside of the bottle achieves the same results.

If you want to merge two lessons into one, you can also use an Alka Seltzer tablet, or vinegar and baking soda, to generate Carbon Dioxide gas inside the bottle, and force the egg out by increasing the amount of gas inside the bottle.

Another common, but erroneous, explanation  can be found on the web and even in some books. In fact, about half of the explanations on the web seem to use this explanation: that the burning material removes oxygen, thus lowering the pressure inside the bottle.  This ignores the fact that, for each molecule of oxygen removed, a molecule of carbon dioxide or two molecules of carbon monoxide are formed.

Some students have argued that it’s gravity that pulls the egg inside the bottle… That’s questionable given that the egg is much larger than the mouth of the bottle, but one easy way to combat that question is actually my favorite way to demonstrate the concept of air pressure.  This idea was shared with us by science teacher, Jeff Feidler of Ursuline Academy in Wilmington, DE.

Cut a small piece from the large end of the egg so that it stands easily.  Place a birthday candle in the narrow part of the egg and ignite the candle.  Lower the bottle onto the egg so that bottle touches the surface of the egg.  As the candle extinguishes, air pressure should be sufficient to allow the bottle to be lifted while the egg is hanging on.  Due to the lower air pressure inside the bottle, the egg will remain in the opening of the bottle.  Hold the bottle steady. The egg will eventually be pushed upward into the bottle.  This version of the demonstration will take a little longer than the traditional method detailed above, but is a great way to celebrate birthdays in your classroom…..and to show that gravity is not the explanation!

Educational Innovations sells these hard-to-find milk bottles for an additional activity that utilizes a  one way mesh screen.  Water can be poured into a bottle covered with a screen, and when the bottle is inverted, the water doesn’t come out!

Procedure:
1. With an elastic band attach a double layer of nylon net screen to the top of a milk bottle.
2. Show students that water can easily be poured into the bottle through the screen.
3. Place a small piece of card stock (ca. 7 x 7 cm; 3 x 3″) on top of the
screen, hold it in place with your hand, and invert the bottle over a sink or bowl.
4. Slowly slide the card out.
5. Ask students why you can you pour water into the bottle, but when inverted the water does not flow out?
6. Tip the inverted bottle slightly and then bring back to the upside down position. The water will begin to flow out of the bottle while it’s tilted and then will stop flowing when the bottle is back in the starting position.

Why does this happen? The force of flowing water allows the water to enter the bottle through the screen. Water in motion tends to remain in motion.  When the bottle is inverted, the water stays in the bottle because the molecules of water have a greater attraction to themselves than to the screen. The water is said to exhibit surface tension. In addition, when the bottle is inverted, a small amount of water is lost from the bottle, the air which remains at the top of bottle slightly expands, and the pressure of the air inside the bottle is slightly less than the outside atmospheric pressure. The combination of the water’s surface tension and the greater outside atmospheric pressure explains why the water tends to remain in the bottle. When the bottle is tipped slightly and then returned to the upright position, outside air enters the bottle and water runs out until the forces return to static equilibrium.

Whether you have your own bottle or choose to purchase one from Educational Innovations, you can have tons of science learning fun with your students in almost every grade level!

## Density Activities With The W-Tube

February 12, 2010

by: Tami O’Connor

The W-Tube is a device that was invented and developed by Ron Perkins, Chemistry and Physics high school teacher for 33 years and founder of Educational Innovations.  This amazing teaching tool was designed to have students in every grade level, kindergarten through high school, discover and gain a deeper understanding of concepts relating to density and air pressure.

In order to solve each puzzle, students need to have a basic understanding of density and air pressure.  Depending upon the grade level of your students, you may want to conduct a few experiments or demonstrations prior to having them attempt the W-Tube challenges on their own.  The following two activities do not utilize the W-Tube, however they will provide some younger students with the background knowledge necessary to successfully complete the W-Tube challenges.

This first activity is a valuable demonstration that shows that air takes up space.  Start by balling up a paper towel or tissue and affixing it to the bottom of a plastic cup using two-sided tape.  Invert the cup with the tissue inside and then push the plastic cup into a clear container of water so the cup is completely submerged.  Your students should be able to see that, although the air is somewhat compressed within the cup, the paper at the “top” of the cup remains dry.

The second activity deals more with density, or how tightly packed the molecules are in a given object.  An object’s density is determined by comparing its mass to its volume.  For example, if you have two objects of the same size, the heavier object is said to be more dense.

Pour equal amounts of corn syrup, water and vegetable oil, into 3 different but identical beakers, and, using a balance, find the mass of each liquid.  Then, gently pour the liquid with the second heaviest mass into the beaker with the liquid with the greatest mass.  Finally, add the third liquid, which has the least amount of mass, to the beaker.  The three liquids should remain neatly layered according to their density, indicating that the less dense liquid floats on the liquid that is more dense.  This activity can also be conducted using different colored water with varying amounts of sugar in each, which would change the liquid’s density.

The W-Tube Puzzle is an excellent addition for any science table and is also great to use with students working in small groups.  The apparatus (DEN-510) contains three connected tubes that form a W.  The central t-connector between the three tubes allows water and air to move through freely.  Because air and water each take up space, by capping one or more of the tubes, you can trap the air and/or water such that they are no longer able to flow freely.  This gives the student the ability to vary the amount of water and air in each individual tube.

Activity 1 – Air Pressure

Students, working in small groups, should use pipets to fill the W-Tube with colored water in order to replicate the following diagrams.  Students should check with the teacher before emptying the W-Tube and moving on to the next diagram.  By strategically placing a cap on specific tubes, one can trap water and/or air to fill the each tube at a different level.  See the diagrams below.  The challenges become increasingly more difficult as you move down the list.  If a group of students complete their challenges quickly, ask them to replicate Challenge #3 using only one cap.  It can be done, but it is more challenging!

Air Pressure Challenge #1

Air Pressure Challenge #2

Air Pressure Challenge #3

Air Pressure Challenge #4

Air Pressure Challenge #5

Air Pressure Challenge #6

Activity 2 – Density

Provide each group of students with a beaker of sugar, food coloring (red, blue, and yellow), 3 small cups, a pipet, a spoon for measuring and mixing, and a source of water. Using the W-Tube (and the caps needed), students should alter the amount of sugar in each cup of colored water to replicate the picture provided.  For example, since the diagram shows the blue water as the bottom layer, it is the denser liquid (and has the most sugar).  Encourage your students to use as few caps as possible to complete each challenge.  Students must keep the W-Tube apparatus firmly on the table at all times during the activity (no tipping except to empty between trials).  Advanced students should develop a written plan before attempting the challenge.

Density Challenge #1

Density Challenge #2

Density Challenge #3

Density Challenge #4

For more information, and/or to view the teacher’s and student’s guides, visit our website: www.teachersource.com.