Air Powered Projectile in-depth look [W/Video]

The Air Powered Projectile in-depth look

One of the best ways to engage your students in the study of projectile motion is with direct experiment and observation. For this purpose I recommend the air-powered projectile. It safely and reliably demonstrates projectile motion by simply releasing compressed air. Here are five experiments to get you started.

launch
The soft nose cone provides a high degree of safety while the body’s sleek design minimizes the effects of air resistance.
soft_nose

MEASURE LAUNCH VELOCITY
Shooting the projectile straight up is the easiest way to determine launch speed.
The first thing you want to do is determine the launch velocity by shooting straight up. It takes about 5 seconds to go up and come back down when shot vertically. Use the formula v=vo+at , analyze the top of the trajectory. At this point velocity = zero. Then set gravity to negative 10m/s/s. Gravity is pulling opposite the initial launch velocity, which is the unknown. Plugging in 2.5 seconds for time (assuming the trip takes the same time up as down) we get a launch velocity of about 25m/s. You might be concerned whether this is a safe speed, but the soft nose c one, and the fact that there is no chemical propellant ensures this. You may wish to wear safety goggles anyways.
launch-1

The calculation of launch velocity is straight forward, requiring only algebra.
algebra

ANGLE vs RANGE
A classic experiment that I have done every year since I started teaching is to investigate which angle generates the greatest launch distance. Students will have their own hypothesis. Without doing any math, try to hypothesize which angle will maximize the range. This is an experiment that works in both high school and middle school. The theoretical result is that 45 degrees maximizes range.

r-a

Sample data for the Range vs Angle Experiment. Note the systematic error on the zero.
This is because the product of horizontal velocity and time in the air is maximized. The mathematical proof is a common homework problem in Honors Trigonometry classes and can be done without calculus. When you plot the data, a surprising result is that the complementary angles, like 30 and 60 degrees can have the same range as each other. This is because when the velocity is more horizontal, the vertical time is lessened, and vice versa.

wedges

Angled Wooden Wedges help a lot in this experiment. The angle of launch will be the compliment to these angles.
When performing this experiment, it is helpful to use the angled wooden wedges option. These help adjust the angle without the use of clumsy blocks of wood or coupling. Another addition you might want to invest in are the varied speed end caps. The different size caps affect the pressure limit that causes the seal to slip, launching the tube upward with the force of expanding gas. Larger endcaps can capture more of that force so it will go faster. This adds another variable which allows you to make new predictions. But with the same endcap, you get the same time, every time.

caps

Different sized end caps can change the launch velocity, adding a new variable.
ADIABATIC EXPANSION
The air powered projectile does not use any chemicals to launch. It only uses the compressed air of a bike pump, typically around 60 psi (pounds/square inch). When you launch the projectile, you will usually see some clouds appearing beside the base. They only last for a second, but can be made more visible by using a high speed camera. (Many students now have these in their smartphones.)

Adiabatic

Adiabatic clouds appearing during a typical launch event. This image was taken with an iPhone 5s in 120 frames/second mode.
The clouds are caused by the humidity in the air being turned into a vapor due to the rapid temperature change. When a gas expands rapidly, it cools. This is called adiabatic expansion. It is an important idea in thermodynamics and this is a really good example of it. You’ve probably seen it when you open a champagne bottle, or even a soda.

Because the force of launch only acts in the initial moment, the rocket is an excellent example of a free falling projectile (unlike missiles and rockets). The sleek profile minimizes air resistance and turbulence while increasing the accuracy of the experiment.

HIGHLY ACCURATE CALCULATED LANDING SITES
In video we launch the air powered projectile at 30 degrees, and from the first experiment, we already know the initial velocity, Vo=25m/s. We use Vo sin30 to find the initial upward velocity (12.5m/s) and Vo cos30 to find the horizontal component (21.6 m/s).

board

A typical projectile motion problem can now be performed experimentally, with a high degree of accuracy and while being highly engaging.
At the highest moment, it is only moving horizontally, so we once again can use v=vo+at. Only this time the plug step is 0=12.5-10t giving a time of 1.25 seconds to reach the top. Twice that is 2.5 seconds, the total time of flight.
The product of the horizontal component and the total time of flight is the distance traveled. (The horizontal velocity never changes.) The range, x=vhoriz * time = 21.6m/s * 2.5 sec = 54 m.
That the theoretical prediction. Take it with you, and some measuring tape (or the yard lines on the football field) and see what really happens.

field

The impact location proves to be within 2 meters of the expected value.
When we did the experiment we got a result of 56 meters. That is less than 4% error, very good!


james_lincolnJames Lincoln

Tarbut V’ Torah High School

Irvine, CA, USA

James Lincoln teaches Physics in Southern California and has won several science video contests and worked on various projects in the past few years.  James has consulted on TV’s “The Big Bang Theory” and WebTV’s “This vs. That”  and  the UCLA Physics Video Project.

Contact: [email protected]

 


 

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Boyle, Charles and Cans… Oh, How I love the pressure!

You may have tried the can crushing pressure demo, you may have even tried it with a 55 gallon drum, but have you tried an entire tanker truck?   In the December CoolStuff Newsletter, Bridgette Sparks of Saline High School in Michigan talks about the high pressure environment she has created in her classroom!  Well, at least with the subject matter!

I, too, start my gas unit by having the class participate in a discovery based lab exercise very similar to the “Gas Laws Smorgasboard” mentioned in a previous Cool Stuff newsletter. Towards the end of class, I start playing David Bowie’s Under Pressure or Billy Joel’s Pressure since most of the lab stations are explained using pressure differences. When the students enter the classroom the next day we discuss pressure differences by observing the can crusher demo as a whole class. This time I use a larger paint thinner can and have the class explain using scientific principles. This is followed up with the next two questions and videos:

The air pressure is significant but could we do the same thing with a 50 gallon drum?

Or, how about a tanker car?

About Magdeburg hemispheres


The Magdeburg hemispheres are another cool example of how atmospheric pressure can have a significant effect on Earth. Invented by German scientist and mayor of Maddeburg, Otto Von Guericke in 1656 to demonstrate the concept of atmospheric pressure. By sealing a pair of large copper hemispheres with grease and the air pumped out, the sphere contained a vacuum and could not be pulled apart by a team of thirty horses until the valve was opened to release the vacuum.

The force holding the hemispheres together is equal to ~9000 lbs, equivalent to lifting a car.

Re-enactments of Von Guericke’s 1656 experiment are performed in locations around the world by the Otto von Guericke Society. The experiment has also been commemorated on two German stamps.

After learning about Guericke’s pump, Scientist Robert Boyle, working with Robert Hooke in designing and building an improved air pump. From this, they formulated what is called Boyle’s Law, which states that the volume of a body of an ideal gas is inversely proportional to its pressure.

A very big thank you to our contributors for this article:

Bridgette Sparks,
Chemistry Teacher
Saline High School
Saline, Michigan

Dwight “Buzz” Putnam,
Physics Teacher
Whitesboro High School
New York

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Vortex Rings in nature and your physics classroom!

You’ve probably seen a smoker blow smoke rings or you’ve created whirlpools in your tub or pool when you were little. These phenomena are known as Vortices, formed when a fluid swirls around a central point because of a complex combination of friction and pressure. These Vortex Rings are more common and widespread in nature than most people had probably thought; in fact, they are studied in great detail by aeronautical engineers and combustion scientists. But we just think they are cool! Take a look at the video and then read below as Physics Teacher Buzz Putnam of Whitesboro High School provides more commentary on these amazing natural occurrences:

The video illustrates Vortex Rings being formed by various sources including dolphins and volcanoes. You’ll notice in the video that the Vortex Rings are quite stable until they slow down and then at some critical speed, the core enlarges very suddenly causing the vortex to breakdown. Dolphins make, watch and chase them, even using their flippers to stop them rising in what appear to be games similar to those we humans play with soap bubbles. Watch Mt. Etna emit gigantic ring-shaped clouds of steam and gas up to 200 m in diameter that can fly up to 1000 m high, lasting more than 10 minutes. Your students will realize that humans aren’t the only ones who love to make and watch Vortex Rings, one of the coolest phenomena in nature!

Physics Teacher Magazine thinks it cool too!

The November 2011 cover for Physics Magazine shows the steam ring expelled by Etna’s summit crater.
View Physics Teacher Article>>

 

If you want to bring the vortex ring right into your classroom, you can do so with an Airzooka Air cannon and a fog machine (or fog in a can). Here is our Airzooka Air cannon in action:

Resources:

 

Do more with vortex rings right in your classroom, check out these great links:

BBC News article: Etna hoops it up

The Physics Teacher – Smoke Ring Physics vol. 49, November 2011.

Acknowledgements: Thank you to Dwight “Buzz” Putnam for his assistance in writing this Cool Stuff. Buzz is a 25-year veteran physics teacher at Whitesboro High School, New York Science Teacher of the Year and host of the Regents Physics Answers television show on PBS. You can also find him refereeing high school basketball games as well as presenting at the NSTA national conferences.

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Can a Helium Balloon Defy Physics?

Watch this video and it almost seems like this balloon’s actions are counter-intuitive to everything we know about motion and inertia. Let Professor Joel Bryan from Ball State University explain what is really going on.

 

 

Can’t see YouTube, try watching in Flickr.

Ask any student what happens when they are riding in a car and the car makes a sharp left turn, they’ll probably tell you that they, and everything else in the car that is not tightly secured, will be “thrown” to the right. Similarly, when the car turns sharply to the right, everything tends to be “thrown” to the left. They also probably know by experience that objects and passengers in the car keep moving forward when the car comes to a sudden stop – which is why seatbelts are required – and get “thrown” backward when the car suddenly accelerates forward. Science teachers frequently use these examples in discussions of Newton’s laws of motion, as well as addressing the widely held misconception that there is a “centrifugal” force that pushes the objects outward. If already in motion, the inertia of an object in the car tends to make it continue moving forward – regardless of how the car turns or changes speed. When accelerating the car from rest or some other constant speed, inertia tends to make an object in the car remain at rest or remain at its initial speed.


When students enter your classroom armed with these firsthand experiences, they may not at all be surprised by the video clips showing the direction an air-filled balloon hanging from the ceiling of a van swings when the car makes sharp turns to the left and right. However, they will likely be quite surprised to view the video clips of the motion of a helium-filled balloon inside a moving van as the van turns to the right and turns to the left.


The air–filled balloon hanging from the ceiling of the van behaved exactly as most would expect. The balloon swung to the left when the van turned right, swung right when the van turned left, swung backward when the van accelerated forward from rest, and swung forward when the van came slowed to an abrupt stop. This motion is easily explained using inertia and Newton’s first law of motion.


However, the helium-filled balloon that was attached to the floor of the van surprisingly moved opposite to the direction of the air-filled balloon. It swung to the right when the van turned to the right, swung to the left when the van turned left, swung forward when the van accelerated forward, and swung backward when the van accelerated backward (slowed abruptly to a stop).


One may initially think that this is a violation of Newton’s first law of motion, but the first law not only holds true, it is also useful in explaining the balloon’s behavior. When the van turned sharply to the left, air molecules inside the van continued moving forward and effectively were “thrown” to the right side of the van. This resulted in a greater density of air molecules on the right side of the van than on the left side of the van. The greater density of air molecules on the right side of the van created a buoyant force that pushed the lighter than air helium balloon from the greater density right side toward the lower density left side of the van. For similar reasons, the helium balloon swung to the right when the van turned sharply right. Once students understand this explanation, they should be able to predict and explain the movement of helium and air–filled balloons when the van speeds up and when it slows down.

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Duke students find a way to walk on water… Well, not quite.

The students of Duke University filled a pool with a mix of cornstarch and water to create a non-Newtonian fluid known as”oobleck”. When stress is applied to the liquid it exhibits properties of a solid. Watch as they walk, run and jump on this amazing fluid!

As the YouTube video below shows, stopping or even slowing down while on the stuff can lead to a sinking sensation!

Fluids Behaving Strangely

Key Concept: Non-Newtonian fluids are so named because their properties cannot be described in terms of the concepts of classical fluids. Unlike normal Newtonian fluids, these materials possess properties that depend on how gently or strongly they are stirred or pulled. The study of the flow of materials that behave in this unusual manner is known as rheology.

Quicksand is a common example of a non-Newtonian substance that tends to solidify when placed under stress. The harder a person thrashes around to get out, the worse matters become. Ketchup, on the other hand, behaves in the opposite way. The more it’s shaken, the more readily it flows.

Shear Madness

Oobleck Station Reading is FUNdamental Pittsburgh, Junior League Member VolunteersWhen some non-Newtonian fluids experience a sideways force known as shear, they tend to solidify. A mixture of cornstarch and water is such a fluid. Known to many as Oobleck, this strange substance offers students an opportunity to become amateur rheologists. To make Oobleck, students will need 1 cup of cornstarch, 1/2 cup of water and, if desired, food coloring. Instruct them to:

1. Put cornstarch in bowl.

2. Slowly and while stirring (hands are fine) add the water.

3. Add food coloring as desired.

Once your students have made their Oobleck, you may wish for them to try the following experiments.

1. Have them test the Oobleck by hitting it hard, then softly. They should then stir it quickly, then very slowly.

2. After pouring some of the Oobleck on the table, have students push on the puddle with the side of their hand. The Oobleck will become a solid with the application of a force, but will return to its liquid state as soon as the force is removed.

3. Have students attempt to pick up some Oobleck. Once they have it in their hands, ask them to try to keep it in solid form by continually kneading it.

4. Have students play catch with Oobleck. They will notice that as soon as they stop kneading the Oobleck it will return to its liquid state. This is very obvious as it flies through the air and is caught.

For something that is sure to delight your students you may wish to have them…

Shake it Up: Animating Oobleck with Sound Waves

As you have seen, when stress is applied to a mixture of cornstarch and water it exhibits properties of a solid. Especially interesting is the effect produced when the mixture is disturbed at certain frequencies.

To produce effects that have to be witnessed to be believed, you will need a function generator, an amplifier, a subwoofer and a dish or pie tin containing a mixture of cornstarch and water (Oobleck). You may wish to begin with a mixture of two parts cornstarch and one part water.

Support the container containing the Oobleck over the top of the subwoofer. Begin your experimentation with a 50 Hz signal and adjust until fingers of Oobleck begin to rise from the surface of the liquid. Here are some video examples of some incredible phenomena resulting from the acceleration of Oobleck with sound.

Interesting Links: 

Thanks to Chris Chiaverina for contributing to this article

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Fluid Mechanics

“Everything flows and nothing abides; everything gives way and nothing stays fixed.”
-Greek philosopher Heraclitus of Ephesus

We live in a world of fluids, i.e., substances that can flow. Unlike solids, fluids have no definite form but instead assume the shape of their containers. Fluids include all liquids and gases and a rather strange state of matter called plasma, an ionized gas that scientists believe accounts for 99% of the matter in the visible universe.

The importance and pervasiveness of fluids cannot be overstated. The Earth’s atmosphere, oceans and core are fluids. We breathe and drink fluids. We sail ships in them and fly planes in them. We are entertained by images on our plasma televisions, illuminated by the glowing plasma in fluorescent lights, and awed by the amorphous streams of charged particles found in lightning.

Fluids are described by properties such as density, viscosity, and compressibility and are responsible for familiar phenomena that include pressure, buoyancy, and aerodynamic lift. The characteristics associated with fluids derive from the relatively weak interactions between their constituent particles. Atoms and molecules found in fluids are not bound to fixed positions

Some common materials known as non-Newtonian fluids don’t follow conventional laws of flow. With cornstarch and water, bread dough and peanut butter, resistance to flow changes with applied force. Silly Putty will ooze like a viscous liquid but, when pulled apart quickly, it will stiffen up and break cleanly in two. Other non-Newtonian fluids such as paint and mayonnaise flow more readily when disturbed.

The advances made in the understanding of fluids have been substantial, but we have much to learn. Understanding the transport of fluids across biological membranes, the airflow around the outer surfaces of airplanes and rockets, and the dynamics of our oceans, atmosphere, and convection in the Earth’s mantle provide ongoing challenges.

The study of fluids is one of the oldest branches of the physical sciences. Despite its long history, it continues to fascinate scientists and lay people alike. In this edition of CoolStuff we offer ways to engage your students in the study of fluids.

Spanish TV Star Pablo Motos promised his audience that he would walk on water…Well, not quite. They filled a pool with a mix of cornstarch and water (a non-Newtonian fluid). When stress is applied to the liquid it exhibits properties of a solid.

Under Pressure

Key Concept: Pressure is force per unit area. Atmospheric pressure is defined as the force per unit area exerted against a surface by the weight of the air above that surface.

Atmospheric Pressure Mat

A simple rubber mat provides an extremely effective means of demonstrating atmospheric pressure. The demonstration, devised by John MacDonald of Boise State University, employs a sheet of soft rubber with a handle at its center. The rubber sheet is square, about a foot on each side, with a 50-gram mass hanger poked through the center.

When the rubber sheet is placed on any perfectly flat surface – the top of a lab stool works extremely well –  students find that picking up the rubber by a corner is an easy task. Lifting the corner allows air to get under the mat as it is lifted, thus equalizing the pressure on the top and bottom of the mat. But lifting the mat by the middle is another story. As the middle is raised, a low-pressure region is formed because air cannot get in. The greater external atmospheric pressure forces the mat and stool together. In essence, the rubber sheet behaves as a suction cup, and the entire stool is lifted when the handle is raised.

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Garbage Bag Hug

At sea level, the Earth’s atmosphere presses against each square inch of an object with a force of approximately 14.7 pounds per square inch. The force on 1,000 square centimeters (a little larger than a square foot) is about a ton! We generally go about our daily business unaware of this persistent pressure. The Garbage Bag Hug just might change all that!

Image: Students of physics teacher Shannon Hughes are shown here sharing a “Garbage Bag Hug”. Barrington High School ~ Barrington IL.

  1. Have a student step inside a heavy duty garbage bag (see figure above). Make sure the
    student sits down with arms crossed. After the hose from a Shop Vac is inserted in the top of the bag, the student should hold the neck of the bag tightly around their throat so as to
    form a tight seal.
    (Note: this demo should never be done with the bag covering the head.)
  2. Once the student is inside the garbage bag, use the Shop Vac® to remove the air from inside the bag. Removing air from the bag essentially vacuum seals the student. The external air pressure is often so great that the occupant of the bag is completely immobilized. Safety dictates that a spotter be prepared to catch the encased student should tipping occur

Bernoulli’s Principle: Fluids on the Move

Key Concept:
The pressure in a moving fluid decreases as its speed increases, and increases as speed decreases.

A sheet of paper may be used to illustrate Bernoulli’s Principle. Hold the bottom of the paper with both hands. Now blow over the top of the paper. Since air moving over the top of the paper exerts less pressure than the still air on the underside, the greater pressure below will result in lift and the paper will rise. This is essentially how lift for an airplane wing is produced.

A rather maddening consequence of Bernoulli’s Principle occurs when high winds pass over the top of an umbrella. The fast moving air exerts less pressure on the upper surface of the umbrella than the relatively calm air exerts from below. The result: an inverted umbrella.

There are so many wonderful demonstrations of Bernoulli’s Principle that we found it hard to choose. Here are four that are sure to please your students.

The Bernoulli Bag

A long plastic bag nicely illustrates Bernoulli’s Principle. If you were to blow the bag up by placing it firmly to your mouth, many lung-fulls of air would be needed. But when you hold it in front of your mouth and blow, air pressure in the stream you produce is reduced, entrapping surrounding air to join in filling up the bag. So you can blow it up with a single breath! This is especially effective after your students have counted many of their own breaths attempting to fill up the bag!


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Key Concept:
A fluid exerts an upward force on every object in it equal to the weight of the fluid displaced by the object. This is basis of buoyancy.

Cartesian Condiments

Most everyone is familiar with the Cartesian Diver, named after the French philosopher Rene Descartes (1596-1650). A vial of some sort (a medicine dropper or pen cap work well) is filled with water until it just floats. The vial (diver) is then placed inside a 2-liter soda bottle and the bottle sealed. When the walls of the bottle are compressed, the diver sinks. When pressure is removed from the walls of the bottle, the diver rises.

The Cartesian diver is a wonderful teaching tool for it not only demonstrates Archimedes’ Principle (i.e. buoyancy), but the variable compressibility of gases, the relative incompressibility of liquids, and implications of Pascal’s Principle as well. Squeezing on the top of the sealed plastic container decreases the volume and therefore increases air pressure above the water. By Pascal’s Principle, that pressure is transmitted to all parts of the container. This increases the pressure inside the small glass vial. The increased pressure decreases the volume of air at the top of the vial, and in so doing, decreases the amount of water displaced by the vial. This decreases the buoyant force on it enough to cause it to sink.

Cartesian divers that use packets of condiments rather than glass or plastic vials offer an engaging, no-cost way to get students engaged in learning about buoyancy, and the properties of fluids in general.

Have your students bring in empty 2-liter soda bottles and packets of condiments from restaurants. Encourage students to bring a variety of condiments. Catsup, mustard and soy sauce are easily found. (Note: Individually wrapped Miniature Milky Ways are reported to also work. Why not have your students experiment!)

Students should test their packets’ worthiness as divers by placing them in a bowl of water. Good divers are those that barely float. After a good diving candidate has been identified, it should be placed in a 2-liter plastic bottle (The packet may need to be folded in half lengthwise to get in through the opening). After filling the bottle to the brim with water, students should screw the cap on tight and squeeze the sides of the bottle.

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Did you know…

In 1593, Galileo found himself in dire need of money. In fact, he was only a few steps away from Debtor’s Prison. Out of necessity, he needed an invention that would net him a tidy profit. To that end he proceeded to develop a device to raise water from aquifers. During the process, he stumbled upon the basis for a rudimentary thermometer. In the end, his water pump found no market, but he did succeed in finding a method for measuring variations in temperature.

See a simple Galilean Thermometer demo

Galileo Takes the Temperature
A beautiful instrument, known as a Galilean thermometer, relies on buoyancy to measure temperature. The device consists of a sealed vertical glass cylinder mostly filled with a clear liquid. In the liquid are colorful glass bulbs, each having a precise density and a tag indicating a particular temperature. As the temperature changes, the glass bulbs rise and sink. The temperature is read by looking at the tag attached to the lowest floating bulb.

Like a Cartesian diver, or any other object in a fluid, the only factor that determines whether an object will float or sink is the object’s density in relation to the density of the fluid displaced by the object when submerged. If the object’s density is greater than the density of liquid displaced, the object will sink. If the object’s density is less than the density of liquid displaced, the object will float. If the object and liquid have the same density, a condition called neutral buoyancy, the object will remain suspended at a certain depth without rising or sinking. Neutral buoyancy is achieved by fish, sunken logs, scuba divers and submarines.

The density of liquids varies slightly with temperature. As the temperature increases, the density of a liquid will decrease and vice versa. This is the key to the operation of the Galilean thermometer. As the liquid changes temperature it changes density and the suspended weights rise and fall to stay at the position where their density is equal to that of the surrounding liquid. The lowest glass ball has the greatest density, so this sinks first as temperature rises. The correct temperature is read from the lowest floating ball in the top half of the thermometer.

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Up, Up and Away! Building Your Own Hot Air Balloon
When I was in high school, a friend of mine and I saw an intriguing ad in the classified section of Popular Science magazine. The headline on the ad read “Build Your Own Hot Air Balloon!” To say that we were intrigued by the offer would be an understatement, so we immediately ordered the $1.00 plans for the project. Little did we know that the investment would bring us hundreds of hours of fun, fascination and fleeting fame. In all, we constructed six tissue paper balloons ranging in height from 9 to 28 feet.

The images below show a “Student Built” Paper Hot Air Balloon. Below Balloonist “Conner” is inflating his balloon with a hair dryer.




Image: Left image shows pre-launch hair dryer inflation technique. Above shows launch. Images by Karin Laurel of Woodinville WA.

You may wish to share this engaging example of buoyancy with your students. Building hot air balloons fashioned from tissue paper may be used as a class activity or an extra credit project and need not cost much money. See Brian Queen’s Building and Flying Paper Hot Air Balloons at members.shaw.ca/castlepaperandpress/balloons.htm for complete instructions on building a hot air balloon.

Fluids Behaving Strangely

Key Concept:
Non-Newtonian fluids are so named because their properties cannot be described in terms of the concepts of classical fluids. Unlike normal Newtonian fluids, these materials possess properties that depend on how gently or strongly they are stirred or pulled. The study of the flow of materials that behave in this unusual manner is known asrheology.

Quicksand is a common example of a non-Newtonian substance that tends to solidify when placed under stress. The harder a person thrashes around to get out, the worse matters become. Ketchup, on the other hand, behaves in the opposite way. The more it’s shaken, the more readily it flows.

Shear Madness

When some non-Newtonian fluids experience a sideways force known as shear, they tend to solidify. A mixture of cornstarch and water is such a fluid. Known to many as Oobleck, this strange substance offers students an opportunity to become amateur rheologists.

Image courtesy of “Reading is FUNdamental Pittsburgh Junior League Member Volunteers at the Oobleck Station.

To make Oobleck, students will need 1 cup of cornstarch, 1/2 cup of water and, if desired, food coloring. Instruct them to:

1. Put cornstarch in bowl
2. Slowly and while stirring (hands are fine) add the water.
3. Add food coloring as desired.

Once your students have made their Oobleck, you may wish for them to try the following experiments.

  1. Have them test the Oobleck by hitting it hard, then softly. They should then stir it quickly, then very slowly.
  2. After pouring some of the Oobleck on the table, have students push on the puddle with the side of their hand. The Oobleck will become a solid with the application of a force, but will return to its liquid state as soon as the force is removed.
  3. Have students attempt to pick up some Oobleck. Once they have it in their hands, ask them to try to keep it in solid form by continually kneading it.
  4. Have students play catch with Oobleck. They will notice that as soon as they stop   kneading the Oobleck it will return to its liquid state. This is very obvious as it flies through the air and is caught. For something that is sure to delight your students you may wish to have them…

Run on Oobleck

After learning of the amazing properties of Oobleck, students in my physics class thought they should be able to walk on the stuff… and they did! They made a large batch of Oobleck in a plastic container intended for mixing cement. After taking off their shoes and rolling up their pant legs, off they went! Even though they knew it should work, students were still thrilled to see that they could run across the Oobleck without sinking. As the YouTube video above shows, stopping or even slowing down while on the stuff can lead to a sinking sensation!

Shake it Up: Animating Oobleck with Sound Waves
As you have seen, when stress is applied to a mixture of cornstarch and water it exhibits properties of a solid. Especially interesting is the effect produced when the mixture is disturbed at certain frequencies.

To produce effects that have to be witnessed to be believed, you will need a function generator, an amplifier, a subwoofer and a dish or pie tin containing a mixture of cornstarch and water (Oobleck). You may wish to begin with a mixture of two parts cornstarch and one part water.

Support the container containing the Oobleck over the top of the subwoofer. Begin your experimentation with a 50 Hz signal and adjust until fingers of Oobleck begin to rise from the surface of the liquid. Here are some video examples of some incredible phenomena resulting from the acceleration of Oobleck with sound.

Interesting Links:

Non-Newtonian Substances

http://www.youtube.com/watch?v=cuzn8wh8Fys

Buoyancy

http://www.exploratorium.edu/snacks/iconfluids.html

http://members.shaw.ca/castlepaperandpress/

http://www.youtube.com/watch?v=3dcrCz4ZMfM

Experiments with Fluids…and Other Things

http://scifun.chem.wisc.edu/HOMEEXPTS/HOMEEXPTS.HTML

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Chemistry: Gas Laws Smorgasborg

The activities that follow represent the exploratory phase of the learning cycle approach. These activities introduce students to the behavior of gases in different situations so that they may draw their own conclusions before being given formal instruction in gas laws.

One of the challenges of teaching chemistry is making the invisible world seem real and relevant to our students. Labs present the best opportunity to demonstrate this, but too often we, out of necessity, begin each lab with a litany of “don’ts” (don’t eat food in the lab, don’t touch the acids, don’t look at the bright light being given off, etc) and it is rather rare that the material we study in chemistry lends itself to an experiential approach. I put this lab together because I was so inspired by Chris’ “smorg” concept. I wanted to see if I could generate the same kind of enthusiasm and elicit the “ah-ha” moments from my chemistry kids as he routinely does with his physics students.

The active engagement with the phenomena in this lab is important in helping students confront their own preconceptions and or misconceptions and allows them to test their personal theories. The hardest part is resisting the temptation to give students the “answers” because they are so excited and get deeply involved in developing such interesting (read wacky) explanations.

The fun of watching the kids jump up, shouting a Seinfeldian “Get out!” when someone actually breaks a meter stick in two, listening to the surprised shrieks of students who successfully propel a potato slug across the room and watching happy students munch popcorn while they try to figure out why the kernels pop are all worth the extra set-up time you’ll need to devote to this lab. Give a few kids some mole money (extra credit) to stay after school and help you clean up. Have fun!

Station 1 The Cartesian Diver

Key Concept ~ When the pressure on a gas is increased, its volume will decrease.

Single Cartesian Diver

In Stock SKU: P1-2000
$2.95

Set up a Cartesian diver in a soda bottle. Fill the bottle with water all the way to the top. Fill the diver with just enough water so that it barely floats on the surface. When the bottle is squeezed, the pressure increases on the air trapped in the diver. When the density of the air (gas) changes (increases), the diver sinks to the bottom (whether the bottle is sealed or not). Releasing the bottle releases the pressure.

Instructions:

The “diver” is the little tube half-filled with water inside the large plastic bottle. Note the position of the diver inside the bottle as the bottle sits on the table.

Questions:

Now, squeeze the plastic bottle. What happens to the diver?

Now, take your hands off the bottle. What does the diver do now?

What do you think causes the diver to behave this way?

Station 2 Microwave Popcorn

Key Concept ~ When the temperature of a gas is increased, its volume will increase.

Students will be micro waving small amounts of popcorn in a clear bowl. Popcorn pops when the moisture inside boils and expands, bursting the kernel open.

Instructions:

Place about two tablespoons of popcorn in the clear plastic bowl. Put the top on the bowl and place in the microwave. Close the microwave door and turn the microwave on high. Watch as closely as you can as the popcorn kernels begin to pop, but of course DO NOT OPEN THE DOOR! As soon as the vigorous popping stops, turn off the microwave.

Questions:

Describe what you see (yeah, I know, but try).

What do you think makes the popcorn pop?

Put your popcorn in a paper bag and then squirt in some butter if you wish.

Station 3 Balloon and the Flask (or Hot Air Ballooning)

Key Concept ~ When the temperature of a gas is increased, its volume will increase. 

Place 10 mLs. or so of water in an Erlenmeyer flask. Stretch an un-inflated balloon over the mouth of the flask (250 mL. flask).

Place the flask next to a hot plate with a thermal (oven) glove so that students can move the flask easily from the hot plate to the ice water. Students will see how an increase in temperature can cause in increase in the volume of a gas.

Instructions:

Place flask on hot plate and let water boil.

Questions:

What happens to the balloon? Why?

Now, put the flask in a beaker of ice and let it cool.

Now what does the balloon do? Why?

Station 4 Life in a Vacuum!

Key Concept ~ When the pressure on a gas decreases, its volume will increase.

This station can use a large vacuum chamber or the small vacuum chamber and Vacuum Pumper shown. Provide a balloon with a small amount of air tied inside. The balloon needs to be small enough that it won’t seal against the sides of the chamber. Students will observe an increase in volume when they decrease the pressure in the chamber.

Instructions:

Observe as a partially inflated balloon is placed inside a Vacuum Chamber, in which the air is slowly evacuated. To do this, simply drop the balloon into the chamber. Place the lid and hand pump on the top and pump the air out. Repeat with a marshmallow and shaving cream. IMPORTANT: clean up your mess!!!!!

Questions:

What happens to all of these objects?

Why do you suppose this behavior occurs?

Vacuum Pumper and Chamber

In Stock SKU: P1-2140
$28.00

Station 5 Iron Man (a.k.a. Magdeburg Hemispheres)

Key Concept ~ The earth’s atmosphere exerts pressure on objects.

Students will observe the strength of atmospheric pressure in this memorable demonstration.

Instructions:

Take the two black rubber cups and slap them together quickly with a lot of force. Now, try to pull them apart using the handles. Ask a friend to pull one end and you pull the other.

Questions:

Can you pull them apart? Why or why not?

Now, “burp” the cups, i.e., allow air to come in the center by peeling the sealed cups from each other.

Now what happens? Why?

Atmospheric Pressure Cups

In Stock SKU: P1-2005
$9.00

Station 6 This Sucks! I’m under so much pressure! (Impossible…Science CAN’T suck!)

Key Concept ~ The earth’s atmosphere exerts pressure on objects.

This station has a few steps. It’s important that you assure that students follow the progression of tasks as laid out. This helps build the acquired knowledge to make the final conclusions. Hopefully, students won’t spill any water, but it might be a good idea to set up this station over a sink. Also make sure each student uses a dry card.

Instructions:

Pour some tap water into one of the cups provided. Obtain a straw and sip some water.

Why does this work?

Now, suck up some water and place your index finger over the top of the straw. Lift the straw out of the cup.

What happens? What causes the water to remain in the straw? 

Fill a Styrofoam cup brim full (overflowing) and place an index cards securely on top. Make sure there is good contact between the card and lip of cup. Now, gently turn the cup sideways.

What happens to the water?

Now, gently turn the cup upside down and carefully let go of the card.

What happens to the water now? How is this possible?

Station 7 Mass a Gas

Key Concept ~ Air is a form of matter and has mass that can be measured.

Along with understanding atmospheric pressure, students can discover that air has mass. As shown in the photo, a liquid crystal temperature strip can be added to show the rise in temperature when the bottle is pressurized.

Instructions:

Attach a Pressure Pumper to an empty two-liter pop bottle. Measure the mass of the bottle to at least the nearest 0.1 gram. Record the mass below.

Pump the pressure pumper 200 times and record the mass of the bottle again.

Questions:

What happened?

Why did the mass change?

Remove the Pressure Pumper and record the mass of the bottle again. Explain what happens.

Pressure Pumper Kit

In Stock SKU: P1-2060
$89.00

Station 8 Ruler of the World!

Key Concept ~ The earth’s atmosphere exerts pressure on objects.

This is another demonstration of the strength of atmospheric pressure. Students won’t believe that the air is stronger than they are! Note: The meter stick will break. Breaking a meter stick makes this activity really memorable, but you might want to use another thin piece of wood.

Instructions:

Take a meter stick and place it on a desk so that it extends a bit over the desk. Place two full sheets of newspaper over the section of the meter stick that remains on the desk. Smooth the newspaper out several times so it lies on the table as flat as possible.

Questions:

Now, try to karate chop the meter stick. What happens?

Why were you able to do that?

Why is the newspaper important?

I didn’t use meter sticks for this because of cost constraints. I used pieces of scrap wood having meter stick dimensions. Also, the student-performed meter stick Karate demo could be potentially risky. Students can get overly exuberant when performing this demo with possible harm to themselves and those around them. I would suggest that a warning or perhaps that students be supervised when carrying out this activity. Safety Glasses are a must.

Meter Stick with Metal Ends 6/pk

In Stock SKU: P1-7062
$26.00

Station 9 Super Duster & Office Buster

Key Concept ~ When the volume of a gas increases, its temperature will decrease.

Obtain a can of compressed “air,” such as those used to clean electronic equipment. As you depress the nozzle, the gas inside (typically an HFC) responds to the reduced pressure by “boiling” or rapidly turning into a gas.

This is an endothermic process so the can gets extremely cold (can even cause frost-bite if you hold it too long.) I like the students to relate this to the phenomenon of water boiling at lower temperatures at high altitudes due to the lower pressure. (Lots of campers know this very well.)

The classic Drinking Bird uses a similar concept and makes a good companion to this station. Simply challenge the students to explain the bird’s motion.

Instructions:

Wrap your hand around one of the duster cans. Make sure your palm is in complete contact with the can. Now, depress the nozzle.

Questions:

What do you feel? Why?

Shake the can. What do you notice?

Try to explain what happens when you depress the nozzle.

Drinking Bird

In Stock SKU: P3-5001
$5.95

Station 10 Computer Terminal ~ Have an Applet!

Key Concept ~ When the pressure on a gas increases, its temperature will increase.

Load the applet from the link below. It has a one-dimensional model of a gas under pressure.

Instructions:

Watch the single gas molecule in the applet. Hit the red “compress” button to lower the piston.

Questions:

What happens to the volume as the piston is lowered? Why?

What happens to the atom velocity as the piston is lowered?

What happens to the temperature as the piston is lowered?

Now, hit the red “expand” button. What happens to the atom velocity and temperature?

What is going on here? Try to explain in your own words.

Station 11 Nice shot Spud!

Key Concept ~ Pressure and volume are inversely related. The volume of a gas decreases as the pressure that the gas exerts increases.

The potato launcher is great for demonstrating this concept because there is a section of trapped gas between the two potato chunks that gets increasingly compressed as the dowel pushes one chunk nearer the other. Eventually the pressure being exerted on the plug end chunk becomes so great that it is fired out of the “launcher”. If a good seal is not made when loading the potato pieces the launcher won’t work. Caution** Be sure to demonstrate this station to students first and warn against pointing the launcher at anyone! (under penalty of bodily torture to the Perp!)

Instructions:

“Stamp” a plug of potato with each end of the Potato Launcher tube. Use the plunger to firmly push one plug into the tube. Try to aim the other plug at the target. Do NOT aim the launcher at a person!

Questions:

What happened?

Why did/didn’t it work?

Push the plunger all the way through to empty the launcher for the next group.

Slip a large washer on to the dowel and use the duct tape to secure. This forms a good hand protector when pushing the plunger in.

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