2000 PSTA Annual Convention
Nov. 29, 30 & Dec. 1, 2000
Seven Springs Mountain Resort
Champion, PA 15622
(814) 352-7777
Assessment: The Next Steps
David Willey
U.P.J. Physics Department
Johnstown, PA 15904
(814) 269-2021
dwilley@pitt.edu
http://www.pitt.edu/~dwilley/bio.html
ORDER OF DEMONSTRATIONS
1. “Sucking” An Egg Into A Bottle
Description
Air pressure is used to push a hard boiled egg into a bottle.
Materials
Hard boil an egg and remove its shell. Place the egg in the dish and pour a little of the oil into the dish, roll the egg around so as to coat it in oil. Make a “spill” from the paper and light it, then drop it in the bottle. Place the egg so that it sits on the neck of the bottle. Observe at first the air being expelled from the bottle and then the egg being forced into the bottle.
Theory
The burning paper heats the air in the bottle, causing it to expand and partially escape, pushing the egg away from the mouth of the bottle as it does so. When the fire is extinguished the gases in the bottle cool down and hence get to be at a lower pressure. The greater pressure of the atmosphere on the outside pushes the egg into the bottle.
N.B. Science never “sucks”, and neither do partial vacuums!!
This demonstration is most often done with a chicken egg, but it can be done with an ostrich egg. An ostrich egg takes about two and a half hours to hard boil, and a bottle with a three and a half to four inch internal diameter neck seems to work best.
2. Toilet Paper And Leaf Blower.
Description
A fast moving stream of air causes the toilet paper from a roll to
be projected as a streamer demonstrating the Bernoulli effect.
Materials
Two Roll Version
Slide the rolls of toilet paper onto the paint roller, with them both
unrolling in the same direction. Unroll a few inches of the paper and check
that the roller is rolling freely. With the rolls unrolling from the top,
as shown in the diagram below, blow a stream of air across the top of the
rolls.
3. Film Canister Explosion
Description
A film canister is launched using carbon dioxide to propel it.
Materials
Put a teaspoon of baking powder (not baking soda) in a film canister. The canister has to be one of the white plastic canisters, not the black ones with the gray lid. To the baking powder add half a canister of water and place the lid on the canister. Shake well and place it lid end down on a flat surface. After a few seconds the canister will be blown several feet into the air, leaving behind a splatter pattern similar to that seen on launch pads when rockets blast off. This is perhaps a demonstration best done outdoors.
Theory
The water and baking powder react and form carbon dioxide, which builds up enough pressure to “pop” the lid from the film canister.
NaHCO3(s) + H+ ---> CO2 + Na+ + H2O(l)
When cooking the sodium hydrogen carbonate contained in the baking powder reacts with hydrogen ions from vinegar, sour milk, or the hydrolysis of a salt.
The ingredients listed on a can of baking powder are:
Description
A drinking straw is pushed through a potato.
Materials
Hold an ordinary drinking straw between your thumb and index finger, as if holding a pencil. This is shown in Figure 1. below.
Theory
When done the second way, the air trapped in the straw tends to keep it inflated and also the blow is directed better along the length of the straw, which, being a cylinder is quite strong in that direction.
5. Lighting A Pickle With Electricity
Description
A pickle is used as a light bulb filament, by putting 110 volts across
it, causing it to glow.
Materials
Cut the female end off an extension cord and then strip about an inch of insulation from each of the wires at that end. Wrap each of the exposed wire around a one inch nail and then push these nails into either end of a pickle, as shown in the diagram below.
Theory
The pickling juices act as electrolytes allowing the pickle to conduct enough electricity to light up.
6. Repairing A Balloon With A Penny And Making It "Orbit" Inside The Balloon.
Description
A hole is poked in an inflated balloon containing a penny. First the
penny is made to "orbit" inside the balloon and is then used to "patch"
the hole, preventing further deflation
Materials
Put a penny into a balloon and the blow up the balloon so that it is fairly firm, but not quite as full as it could be when fully inflated. Tie off the neck of the balloon. Using a sharp pin or needle make a hole in the middle of the thickest part of the balloon, which will be the area directly opposite the neck of the balloon. Lubricate the pin or needle before use and twist it while making the hole. Alternatively this hole may be made before the balloon is inflated. Move the balloon in a circular manner and the coin can be made to roll around the inside of the balloon in a manner similar to the motor bike riders in a "wall of death" performance.
If the penny is maneuvered so as to be at rest and covering the hole the balloon may be inverted and the penny will stick in place.
Theory
The pressure differential between the air on the outside and the air on the inside keeps the penny in place, which effectively seals the hole in the balloon.
7a. Tin Can And Methane Explosion
Description
A large tin can is filled with methane, set on fire and subsequently
explodes.
Materials
Cut a hole, about an inch in diameter in the middle of the bottom and middle of the lid of a tin can. Fill the can with methane gas and then place it on the top of the retort stand. Light the stream of methane that is emitted from the top of the can and then stand back. The flame will burn for a time depending on the size of the can, getting smaller and smaller until it disappears into the can causing the gas air mixture inside to explode, blowing off the can's lid.
Methane (or hydrogen) is less dense than air and hence escapes from the top hole, as the interior of the container must stay at atmospheric pressure, air is drawn in through the hole at the bottom. When the mixture inside, and hence what is escaping at that time, reaches an explosive mixture, the flame goes in the can and the contents "blow up".
7b. Blowing Up An Empty Egg Shell With Hydrogen
Description
An empty egg shell is filled with hydrogen, which is then ignited.
After a short time the egg blows up
Materials
Use the pin to make a small hole in each end of the egg and then blow out the contents of the shell so as to leave it empty. Cut a hole of smaller diameter than the egg in the bottom of a paper cup. Cut a couple of triangular shaped pieces out of the sides of the cup and then invert it and set it on the lab bench. Punch a hole in the film canister’s lid and push the stem of the plastic eye dropper through the hole. The dropper should be a tight fit in the hole. Put on the safety glasses! Place a few pellets of the metal in the film canister and add some dilute hydrochloric acid. Hydrogen will be produced. Place your finger over the hole in the top of the egg and the thin end of the dropper through the hole in the bottom of the egg. When the shell is full of hydrogen place the egg on top of the paper cup as shown in the diagram below and light the stream of hydrogen emanating from the top hole.
Theory
As the hydrogen escapes out of the top hole it is replaced by air entering the bottom hole. When the air/hydrogen ratio in the egg is right for the mixture to explode it does just that.
8. Olive Oil Can Collapse.
Description
A large can is collapsed by atmospheric pressure
Materials
Pour about an inch of water into an empty olive oil can. Boil the water by putting the can on a stove or over a bunsen burner. When the can has completely filled with steam, using gloves, invert it quickly and plunge it into a bowl of cold water. The steam will condense, leaving a partial vacuum within the can. The can will collapse rapidly due to air pressure pushing on the sides of the can.
Theory
A partial vacuum if formed in the can and as atmospheric pressure is almost 15 pounds per square inch the can collapses before much water can enter the can.
This demonstration can be done using a 55 gallon drum and a paddling pool with about six inches of water in it. Rope handles should be fastened to the drum, so that two people may lift and invert it, and care should be taken to let go of the drum very soon after it has been immersed in the water.
Huge forces are involved in this demo and you definitely do not want to get your hand trapped in the folds of the drum when it collapses.
9. Coffee Creamer Fireball
Description
Coffee creamer is mixed with air and ignited
Materials
Fasten about a meter of plastic pipe to a funnel. Put about a tablespoon of Coffee-Mate™ into the funnel and let it run a little way into the tube. Blow the coffee creamer out of the pipe through the funnel, as fast as you can, through a candle flame. A large fireball will ensue. This demonstration does work a little better with lycopodium power, but that is much more expensive, even Disney™ now uses Coffee-Mate™ for their dragons.
Theory
The coffee creamer will not usually burn if a flame is held to some of it in a spoon as not enough oxygen is in contact with it to support combustion, nor is a very large area of it exposed to the flame. Blowing the powder as a fine spray exposes a much larger surface area to the air and mixes a large amount of oxygen with the powder.
A similar demonstration may be done using flour instead of coffee creamer, and used to explain why everyone working in a flour mill has to wear rubber soled shoes and be well grounded, so that no sparks occur.
10. Garbage Bag Strait Jacket.
Description
A person is "imprisoned" in a garbage sack by atmospheric pressure.
Materials
Cut one end from a garbage sack so as to leave a tube. Fasten the other sack to the first, using the duct tape, so as to form a single bag, twice as long as a regular bag. An alternative to this is to use the type of bag sold in hardware stores, made for putting in debris from a construction site. Half way down the bag make a hole and using the duct tape seal the end of the hose from the shop vac into the hole. A square of cardboard with a similar sized hole should be fastened to the end of the hose inside the sack to prevent the plastic of the sack from being "sucked" into the pipe. Have a person stand in the sack and hold the end of the hose in one hand, while holding the neck of the bag tightly around their throat with the other hand.
This is not a demonstration to perform with a person who is claustrophobic or otherwise can not deal with confinement.
Turn on the shop vac so as to remove the air from the garbage sack. This traps the person inside and prevents them from moving much.
Theory
Atmospheric pressure on the outside of the bag effectively vacuum seals the person in the bag, providing a very vivid demonstration of the size of the pressure exerted by the atmosphere.
11. Model Rocket Engine
Description
A model of a rocket is constructed using a 5 gallon water bottle for
the combustion chamber and ethyl alcohol as the rocket’s fuel. It is then
used to demonstrate Newton’s third law.
Materials
Pour about 25 cc's of ethanol into 5 gallon water bottle. Close off the neck of the bottle using a piece of a plastic sandwich "baggy" and an elastic band and then shake the bottle vigorously to distribute the alcohol. When the flame from a propane torch is applied to the neck of the bottle the gases inside ignite and the bottle becomes a rocket engine for a short time, (NASA uses the demonstration.) If a set of wheels are fitted to the bottle it can be propelled across a classroom floor, or it can be hung from a pair of strings as a pendulum.
Theory
The gases exiting the bottle push against the sides and bottom of the bottle, they in turn are pushed out of the bottle. Simply put, the bottle pushes the gases one way and the gases push the bottle just as hard but in the opposite direction.
12. Soda Bottle Fountain
Description
A fountain is made by dropping a few Lifesavers™ into a bottle of Coke
Cola™.
Materials
Drill a two millimeter diameter hole in the cap of a bottle of Coke™, Pepsi works well too, but the soda must be of the cola variety. Tie a steel nut to the end of a piece of thin cord. Thread two or three more nuts on the cord and then three or four Lifesavers™. Thread the cord through the hole in the cap, from the inside to the outside, and tape the cord to the cap, so as to be able to replace the cap with the candy inside the bottle, but without the candy coming in contact with the soda. Once outside place the bottle on a flat surface and take off the tape, allowing the nuts and lifesavers to drop into the cola. A stream of cola will be ejected from the bottle.
Theory
The pressure inside a bubble is inversely proportional to the diameter of the bubble. Bubbles therefore cannot form from nothing as this would take an infinite pressure difference. The carbon dioxide dissolved in the cola cannot then escape as bubbles unless there is something for them to form around. The candy acts as center of nucleation for bubbles to form around and soda is sprayed into the air in a fountain approximately 5m in height. This is obviously not a demonstration to do indoors.
Salt poured in beer, or sugar in superheated water from a microwave show a similar reaction. The idea for a bubble chamber, used in tracking nuclear particles also uses this phenomena.
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