Concentrating Sunlight – It’s Easy!

July 9, 2010

by: Martin Sagendorf

On a Bright Day:

A great deal of energy falls on the Earth’s surface – roughly 1 kW per square meter.  This is about 0.6 Watt per square inch.  This doesn’t sound like much energy, but suppose we collect and concentrate 63 square inches of this sunlight?  These 63 square inches would collect about 38 Watts of energy.  This doesn’t sound like much, but…

Suppose We Could Then:

Concentrate these 38 Watts into an area of only 1/8 of a square inch?  This is exactly what we can do with an inexpensive plastic Fresnel lens.  We’ll focus the sunlight into an area 3/8” in diameter – this is the equivalent of 300 Watts per square inch!  With this energy level, we can easily ignite a piece of wood, boil some water, and even melt a penny.

A Suitable Device:

Is described in the book, Physics Demonstration Apparatus and in the blog The Sun’s Energy.

Now we’re going to describe how to build a much simpler version that works just as well – one that uses a very inexpensive Fresnel lens and is very easy to construct.

Much Simpler:

In fact, this version so simple and inexpensive that many setups can be made for little more than the cost of the Fresnel lenses.  For each setup:

A lens board:

  • A plastic Fresnel lens (7-1/8” x 10-1/4”)
  • Two pieces of 11” x 14” corrugated cardboard
  • Some masking tape

For the demonstrations shown:

  • Four spring-type clothes pins
  • A large paper clip
  • A penny (minted after 1981)
  • A (large-tipped) permanent black marker
  • A ½” copper pipe cap
  • Detergent
  • Water (to fill the pipe cap)

The Lens Construction:

It is absolutely necessary that the Fresnel lens be held ‘plane’ so that it may achieve a good focus.  To achieve this, two pieces of corrugated cardboard are used to mount the lens – their corrugations are placed at right angles.

  • Ensuring that the hole outline in each piece is correctly oriented, cut an opening in each which is ½” smaller than the lens – use a single-edge razor blade or a hobby knife.  When laminated, this pair will be much stiffer (and planer) than a single piece of cardboard or two pieces with parallel corrugations.
  • Place the two cardboard pieces together and, using masking tape, tape the hole edges and the outer edges together
  • Place the lens over the opening and tape it over the opening with the grooved face downward (to protect the face from scratches)
  • A NOTE:  It’s a strange property of corrugated cardboard: it always seems to warp – to counteract this I store these lenses under some heavy books

Of Absorbance:

The ‘blacker’ the absorbing surface – the greater the amount of energy absorbed.

Of Thermal Conductivity:

For our purposes, less is better – the object to be heated should be supported such that there is minimal energy loss via the supporting device – hence the use of ‘low-contact-area’ paperclips for holding a penny or a piece of wood supporting a pipe cap.

Igniting Wood:

It really isn’t necessary to make a black spot on wood – it will quickly ignite.  For even faster ignition, use a black marker to make a 3/8” diameter ‘spot’ at the focus location.

A Simple ‘Water Holder’:

We’ll use a ½” copper pipe cap (sometimes called a ‘tube cap’).  However, because the copper is highly reflective, we need to make its surface much darker – the darker the better.

Clean the pipe cap with strong detergent (to remove any residual oil).  Dry it well.  Use the black marker to ‘color’ both the inside and outside surfaces.

Remember to mention to the students that so long as the pipe cap contains water, its temperature cannot exceed the boiling point of water.  But, if the water is boiled off, the cap’s temperature will rise to that which the concentrated sunlight can produce – allowing this to occur may ‘burn’ the cap’s coating – to reuse the cap simply blacken it again.

A Simple ‘Penny Holder’:

Using the black marker, make a (very black) ‘spot’ about 3/8” in diameter in the center of the penny’s face.  Bend (using pliers) the paperclip as shown – note the small ‘hook’ at the end of the inner part of the paperclip, this prevents the penny from ‘squeezing’ out.

In Use:

Good results require a bright & clear sky – even a slight haze will dramatically decrease the sun’s available energy.  Interestingly enough, even the sunlight on a very clear day in the winter will provide sufficient energy for good demonstrations – however, the noonday ‘higher sun’ in the summer months is far better.

Place the object to be heated on the ground.  Two students holding opposite sides of the lens board can position the board for direction and focus.  The ‘altitude’ of the sun will determine the positioning (height and angle) of the lens and the positioning of the object to be heated.  A support for the bottom edge of the lens board will enhance stability (e.g. a box or a stack of books).  It is necessary to focus and maintain the focus for a continuous period (sometimes up to 60 seconds) to achieve the necessary heating time.

The lens must be orientated perpendicular to the sun’s rays, with the object to be heated located directly in-line behind the lens.  A typical Fresnel lens of this type has a focal length of 10” to 11”.  The ‘ruled’ side of the lens must face the sun.

Some Examples:

Focus the sunlight into the smallest spot possible (1/4” – 3/8” dia.).

The sunlight need only be focused such that the whole spot area is smaller than the black surfaces of pipe cap.

Construct the ‘penny holder’ such that the penny is held perpendicular to the light beam.  Focus the sunlight into the smallest spot possible (1/4” – 3/8” dia.).

Some Obvious Cautions:

This lens will produce temperatures in excess of 600 degrees F (300 degrees C)!  Caution students that they must not place their hands (or anything else) within the concentrated sunlight.  It is highly recommended that everyone wear (U-V resistant) sunglasses if they are likely to look directly at the object being irradiated (there can be a great deal of reflected U-V energy).   Advise students not to handle any object that has been heated until it is cooled sufficiently.  For a penny, this can take several minutes.

NEVER LOOK AT THE SUN THROUGH THE LENS ! ! !

These Are:

Great demonstrations for any General Science, Earth Science, Physical Science, or Physics class.  They truly do illustrate the energy in everyday sunlight – energy that we all know is ever-present, but little appreciate its magnitude until we actually witness its concentrated power.  Or:

Truly memorable Solar Energy Labs can be created wherein each group of students is supplied with:

  • A lens board (pre-made)
  • Several clothespins
  • Several paperclips
  • A piece of wood (like, 4” x 4” square)
  • A ½” copper pipe cap (previously cleaned)
  • A U. S. penny (1982 or after)
  • A large-tipped permanent black marker
  • A few mL of water
  • A pair of pliers (for bending paperclips)
  • Sunglasses or darkened glass/plastic (U-V rated)

The assignments:

  1. Discover how quickly how some materials – like wood – can be quickly ignited (time required?)
  2. Construct a support for a penny and melt a penny (time required?)
  3. Boil a small quantity of water (time required?)

Some follow-up questions:

  • “Why does the wood ignite so quickly?”
  • “Why does it take a longer time for the penny to melt (than for the wood to ignite)?”
  • “Why does the water boil so quickly?”
  • “Why is it (sometimes) necessary to have a black surface on the material to be heated by the sunlight?”

A Pre-Lab:

Might include discussions about:

  • Energy (the ability to do work)
  • Solar energy
  • Energy conversions (light to thermal)
  • Absorption/Reflectance
  • Specific Heat
  • Lenses (common and Fresnel)

And possibly:

  • Each group constructs their own lens board

Notes:

  • Remember, the actual exercises must be done on a day when the sunlight is ‘really bright’ – anything less simply will not provide the energy necessary.
  • Always store a Fresnel lens away from direct sunlight – under the correct circumstances it can start a fire.
  • ‘Dusting-off’ the Fresnel must be done with compressed air – wiping with paper or cloth will scrape material into the grooves and diminish its optical quality.

Guidelines for building the Atomic Penny Vaporizer are detailed in the book Physics Demonstration Apparatus.  This amazing book is available through Educational Innovations and includes ideas and construction details, including all equipment necessary, for the creation and use of a wide spectrum of awe inspiring physics demonstrations and laboratory equipment.  Included are 48 detailed sections describing hands-on apparatus illustrating mechanical, electrical, acoustical, thermal, optical, gravitational, and magnetic topics.  This book also includes sections on tips and hints, materials sources, and reproducible labels.

Leave a Comment » | College Level, Energy, Experiments, High School Level, Physics | Tagged: , , , , , | Permalink
Posted by Tami O'Connor

Great Balls and Fire!

June 13, 2010

by:  Tami O’Connor

When two 1-pound, 2-inch diameter, chrome steel spheres are smashed together, enough heat is generated at the point of contact to burn a hole in ordinary paper!  This dramatic demonstration has been a favorite of students in every grade for as long as I have been teaching!

There are a few considerations when allowing students (especially younger ones) to conduct this activity on their own…  First, the spheres are pretty heavy, so if they were either dropped on a foot or onto a nice tile floor, the result would not be good.  Also, be sure that the only thing between the spheres is paper or aluminum foil.  Fingers caught between the colliding spheres would not  be happy.  Finally, all participants should wear safety glasses, as it is not unusual for a small piece of paper to fly off after the spheres collide.

The Procedure:

Have an assistant hold the top edge of a piece of regular white paper vertically.  Hold one sphere in each hand on either side of the paper.  Quickly move the spheres together until they collide against the paper.  If they do not burn a hole in the paper the first time, try again and move the spheres together more quickly.  Examine the hole in the paper.  You will see that the areas around the edges of the hole are actually singed, and you will smell the burning paper!

Repeat the activity; however, this time use aluminum foil in place of the paper.  You will observe concentric circles radiating outward from the impact point.  This is a clear way to visualize shock waves!

Explanation:

This demonstration graphically illustrates how kinetic energy is transformed to heat energy.  Though some sound energy is produced, the force centered at the small where the spheres collide generates enough heat energy to burn the paper.  According to Newton, F=MA.  The amount of force between the two spheres is a function of the mass (which is constant) and the acceleration (which is controlled by the person moving the steel spheres).  The faster one smashes the spheres together, the greater the force.

A note from Ron Perkins:

Some time around 1996, the Smashing Steel Spheres demonstration was presented to a group of teachers in Dr. Larry Peck’s, AP summer program at Texas A&M, taught by Kristen Jones and Lisa McCaw.  One enterprising teacher tried the demonstration later that evening with some old spheres that he had around the house.  Imagine his surprise when he obtained sparks after colliding the rusty spheres together with a piece of aluminum foil held in between.  He had rediscovered the thermite reaction: Fe3O4+Al ->Fe+Al2O3+Heat and Sparks. (the numbers in the equation should be subscript, but there is no way to do this in the program we use for the blog…)

Since then, there has been a frantic search for rusty spheres.  It is possible to rust the Educational Innovations’ spheres, but it is usually a very slow process.  Dr. David Shaw, MATC in Madison, Wisconsin, has reported that a few months in the presence of fumes from the chemical storage closet works well…

Leave a Comment » | College Level, Elementary Level, Energy, Experiments, High School Level, Middle School Level, Physics | Tagged: , , , , , , | Permalink
Posted by Tami O'Connor

An Engaging Demonstration for Reinventing Edison: Build your own Light Bulb

April 19, 2010

by: Bennett M. Harris

It never fails.  I get the same reaction, whether I present to seasoned physicists, grade level science teachers or even from the most discerning audience I’ve had; a group of fifty – fourth grade students, jaws gape and sounds of oohs, aahs and wows issue forth.

I’ve been in rooms surrounded by hundreds of artificial light sources, from the simplest incandescent bulbs to the most advanced OLED displays, and even so, when a person closes that knife switch and current begins to flow and a simple piece of pencil lead held suspended inside a partially evacuated chamber starts to glow brighter, brighter, and finally white light illuminates the chamber, something happens in the person’s brain.  At once they are connected with the wonders that Sir Humphry Davy, Swan, and Edison felt when they experimented with the world’s first electrical light sources.  Questions start to form; How does that work? How could we make it last longer? What would happen if we changed the carbon for some other material?  All at once, the passive viewer is thinking scientifically, asking questions, and yearning to do more.

I’m talking about “Reinventing Edison: Build your own Light Bulb”, a science kit that I am proud to have designed.  I created the kit to be fun and interesting while at the same time integrating history and invention into science and mathematics.  The kit is designed to work as a safe, hands-on, inquiry based science experiment for both qualitative and quantitative experiments.  But It also works well as an engaging  demonstration at the front of the classroom.

Some ideas for demonstrations include:

1)    As an example of science, invention, and history for your grade 3-5 class.

2)    As a day one introduction to your middle school physical science class.

3)    As an introduction to your high school physics class or electricity lessons.

4)    As a demonstration of quantitative data gathering and properties of matter for your middle or high school physical science class.

5)    As an illustration of the scientific method AND proper safety procedures for your technology or engineering class.

6)    As a demonstration to introduce the electricity section of your college physics lecture.

No matter what your grade level or subject area, the Reinventing Edison kit can be a very effective way to create interest in your students, get them asking questions, and help them to get excited about what will come next in your science lectures or labs.

This article will detail some tips and tricks for effectively using the kit as a demonstration based upon my own experience using the kit in front of many different audiences.  I will not go into specific details on how to setup or use the kit as those instructions are included in the instruction and experiment manual that is included with the kit.

First things First: Safety

The Reinventing Edison kit is designed with safety in mind, however as with any science experiment or demonstration there is some risk involved if proper safety procedures are not observed.  Make sure to read, understand, and follow all safety instructions printed in the manual.  Risk of eye injury is minimal, but it is always a good idea to wear eye protection both for your safety and to demonstrate proper lab procedures.

Filaments, especially the carbon and tungsten filaments, will glow to incandescence, potentially emitting a bright white light that can light up a room.  It’s advised that you and your audience never stare directly at the filament after it starts to glow beyond a cherry red color.

Remember filaments and conductors of heat in contact with the filaments will get very hot.  Always allow a minute or more for the filament, clamps, and bulb cap to cool before handling after each experiment.  In this way you will avoid singed finger tips and can avoid uttering things that you shouldn’t in front of sensitive ears (such as the seasoned physicists that I mentioned above).

Always wear a lab coat while performing experiments with the Reinventing Edison kit.  This is in no way a safety issue, they just look cool…

Keep Things Simple

In some of my first demonstrations of the Reinventing Edison kit I made the mistake of trying to cram too much into a short period of time and performed in front of a large audience.  I had volt and current meters set up, multiple power sources, and was prepared to talk for hours about the history of Edison. I forgot my purpose was simply to grab the attention of my audience and not to teach a years worth of electrical engineering and history!  The important lesson that less is more had eluded me.

When using the Edison kit as a demonstration I recommend that you choose a simple configuration (series circuit) with a filament choice that will give a guaranteed result the first time you throw the switch.  The included carbon filament (pencil lead) works best, glows red for a time, and then glows bright white for a minute or more before burning out.

The included tungsten filament glows bright white for a lot longer than the carbon filament, and as a result, might actually have less of an impact than a filament that burns out within a minute or so.  An audience of any age will have their wow moment as soon as the filament reaches incandescence and will usually sit spell bound for about a minute wondering if it will burn out (especially if you keep them going with what you are saying), but they won’t usually last for the three or more minutes that a tungsten filament may last for.  Save the Tungsten filament as a closing experiment and give a quick lecture or answer questions while you wait for it to burn out.

Remember the History!

Reinventing Edison is as much about history and invention as it is about science or math.  I like to start any demonstration by asking the audience to close their eyes and imagine a time when there was no light source except the sun or fire.  When it was dangerous or impossible to travel at night time.  When a forgotten candle might burn down your house.  When you didn’t have electrical devices in your home because you didn’t have electricity in your home.

I then talk about Edison and how creating the light bulb was not solely his achievement.  It’s good to talk about earlier demonstrations that  Sir Humphry Davy performed using giant batteries and carbon filaments for college audiences as well as the contributions of the English chemist Swan.  Edison patented the bulb and all of the systems required to manufacture, distribute, and power them first, but even then, it was not solely his effort.  He had a team of hundreds working for him.

The following link contains a bibliography of sources that I used to research the science and history behind Edison and the Light Bulb.  If you want to learn more I highly recommend the sources listed.

http://www.scribd.com/doc/18219124/Reinventing-Edison-Reading-List

Be Prepared – BUT remember, when things go wrong this is a teachable moment!

Its a good idea to perform your intended experiment by yourself before you have an audience in order to work out any bugs, determine the timing requirements, and learn how to deal with any “surprises” that you may experience.  I’ve found that mistakes or problems while operating the bulb often work to build suspense in an audience and function as “teachable moments” to illustrate science facts.  If you do encounter problems, remind your students that Edison experimented for several years with thousands of different filament materials until he got a bulb to work!

When I demonstrated the bulb to a group of 50 fourth grade students I had wired my batteries incorrectly.  So I talked about the bulb, how it worked, what I was going to do next.  I asked my assistant to dim the lights and then to flip the switch.  And when they did, the filament smoked and immediately exploded into two pieces.  Too much current, too little voltage, no incandescence.  I still got a wow when it exploded (thanks to the camera projecting the bulb onto a larger screen) but not the BIG wow I wanted from the moment of incandescence itself.  Without missing a beat I talked about Edison’s thousands of experiments and asked the audience if they thought two or three tries for us would still be respectable.  I then talked about the problem (parallel batteries instead of series batteries) and told them I would wire the circuit a different way, changing a variable, and seeing what would happen next.  My blunder turned into a “I meant to do that” moment that would have made professor Pee Wee proud.

Get The Audience Involved and Have Fun!

The more interactive your presentation is the better it will be.  Everyone has sat in boring power point slide lectures that left them less intelligent than when they came into the room, and most of us have ended up giving a few of those presentations in our careers, too.  But remember, science is about asking questions.  Ask your audience (the students) questions about what you are doing.  Who invented the light bulb (they’ll say Edison, you can counter with “he is credited with inventing it, but have you heard of Swan?”)  Ask them to predict what will happen next if you change something about your experiment.  Ask for volunteers to verify that the pencil lead you are putting into the bulb is really just ordinary pencil lead.  Get a volunteer to throw the switch or ask the crowd to countdown like a rocket launch.  Most importantly have fun with what you are doing.  You are modeling the idea that science and technology can be interesting and rewarding not just math-filled, difficult, or boring.  If something goes wrong, use it as a moment for comedy.  I had an electronics teacher in high school who every year would work on a TV set during open lab periods and every year he’d cause a huge electrical arc to jump between the high voltage terminal and the chassis seemingly by accident.  He’d then jump up and run away from the bench in fear in a display that would have made Lou Costello proud.  This definitely got students attention and made for a memory that I still have decades later.  Just remember, keep things serious around safety and around facts, but keep things fun, open, and accessible overall.

Don’t forget the vacuum

Your demonstration is likely focused on electricity and light, and hopefully history, but it’s easy to forget what isn’t there… the vacuum!  Achieving incandescence in a filament is dependent upon removing as much air from the bulb as possible.  Air hinders incandescence in three ways; air conducts heat away from the filament such that it does not heat up to the point of incandescence, air can support combustion of materials like carbon and thus causes them to physically burn up quickly, and the oxygen in air can combine with the hot filament material and oxidize it weakening its structure and causing it to burn out more quickly.

Obviously the hand vacuum pump included in the kit cannot remove all of the air in the bulb, but it does remove enough that you can achieve several minutes of operation from carbon and tungsten filaments.  Air is invisible, and so to illustrate the working of the pump you can ask for a volunteer to report their observations. For example, hearing the pump operate, feeling as it becomes harder to move the piston as they remove more air, and feeling for the air that is coming out of the pump.  You can also use the bulb (minus a filament and electrical connections) as a mini-bell jar and use it to boil a small amount of water, inflate a small tied balloon, or expand a marshmallow.

An interesting fact: Many years ago, light bulbs had a nearly complete vacuum, so if they broke they made a very deep implosion sound (check out any black and white film where a light bulb breaks to hear what this sounded like).  Today bulbs are only evacuated to about one fourth atmospheric pressure with the oxygen replaced by the inert gas Argon.

Due to risk of implosion I don’t recommend that you try to use a powered vacuum pump with this kit.

Finally a few technical tips for a good demonstration

We’ve received very few trouble reports from users of the kits since we started making them in 2004, but we have found that 99.9% of all problems have come from using the wrong kind of power supply.  For best results make sure you use two fresh 6-volt Alkaline lantern batteries.  Carbon Zinc batteries are less expensive, but they cannot supply enough current to support incandescence.  Alkaline batteries almost always say “Alkaline” but Carbon Zinc batteries usually just say “Battery”… one way to tell the difference is that most Alkaline batteries have a metal shell and Carbon Zinc batteries have a plastic or even cardboard shell.  Also, make sure you keep up with the cap-covers for the batteries. Cap-covers are plastic insulators that prevent the metal terminals on the battery from shorting out if they come into contact with a conductor.

The top stopper in the kit is designed to pull inside the clear plastic tube should an actual vacuum pump be used with the kit.  This is an intentional design put in place to to avoid any implosion risk.  Since rubber stoppers vary a little bit in diameter and are softer when they are new, your top stopper might pull inside the tube when you use the hand-vacuum pump.  If this happens you can fix the problem by tightening the hex-nuts on the screws that pass through the stopper.  You should also make sure to press the vacuum release stopper as deeply as possible into its port.  This will cause the stopper to expand in diameter a little bit and should reduce its tendency to pull inside the tube.  If the stopper does pull inside the tube, you can retrieve it most easily by removing all wiring and the vacuum pump and then push the stopper through from the top to the bottom of the tube.  This is another reason to assemble and test your kit before going on stage in front of an audience.

Always remember to open the knife switch on the bulb after every experiment.  When the filament burns out it is very easy to immediately jump to changing the filament for your next experiment.  Remember, if you don’t open the switch then you can potentially cause a short circuit while handling the bulb cap, or you may have a hot filament in open air or in your hands while you work with it.  Always double check the knife switch before changing the filament!

For a High School or College level demonstration of the kit, it can be useful to monitor, display, or report the voltage drop across the filament and current drawn by the filament.  This can easily be accomplished by standard bench meters, display meters, or even probeware or data logging equipment.  It is important to make sure that you use equipment rated for the voltage source you are using (usually 10 volts since you will be using 6 volts, and 1-amp or higher for current).  Light levels may also be monitored and compared to voltage/current using data logging or probeware equipment.

For Frequently Asked Questions and Troubleshooting tips you can read or download the following document: http://www.scribd.com/doc/18400229/Reinventing-Edison-FAQ-and-Troubleshooting

Conclusion

Thank you for reading this article.  I hope that you found it interesting and learned at least one or two things that will help you make a spectacular presentation to your students.  Enthusiasm for all areas of STEM education is important, and if we can help inspire just one person all of our efforts were worthwhile.

If you use the Reinventing Edison: Build your own Light Bulb kit in your class, for a demonstration or as a classroom activity we’d love to have your feedback.  Feel free to share pictures, video clips, or comments with us at our Fan Page on Facebook: http://www.facebook.com/HarrisEducational.

About the Author

Bennett M. Harris holds a degree in Technology Education from North Carolina State University and has many years of experience developing educational materials, teaching, and tutoring students of all ages in many different STEM (Science, Technology, Engineering, and Mathematics) topics.  Bennett is the founder of Harris Educational and the originator of Reinventing Science kits.

Leave a Comment » | College Level, Energy, Experiments, High School Level, Middle School Level, Physics | Tagged: , , , , , , , , , | Permalink
Posted by Tami O'Connor

The Sun’s Energy

March 25, 2010

by: Martin Sagendorf

Imagine students’ amazement when they actually see sunlight melt a penny!  This demonstration clearly illustrates the vast amount of energy illuminating the Earth’s surface.  In rough numbers: 70% of the Sun’s incident energy on our outer atmosphere is reflected back into space – only about 30% actually gets to the Earth’s surface.  But, as we experience, this is still a substantial quantity of energy.

Fortunately, this energy (I. R. – Visible – U. V.) is rather uniformly distributed over the Earth’s surface -  thus its overall intensity is such that we have a habitable environment.  However, as we all know, we can concentrate some ‘area’ of this energy to increase the ‘energy per area’ (a measure of this is the temperature of the area of concentrated energy).  A common magnifying lens (2-4 in. diameter) will concentrate sufficient energy to burn paper or other objects with a low flash point.

To achieve an even higher energy concentration it is only necessary to use a device that increases the ‘capture area’ of the Sun’s energy.  Fortunately, this is easily accomplished with an inexpensive ($3.50) Fresnel lens.  The Fresnel lens (64 sq. in.) used here will ‘collect’ nine times the energy of a 3 in. diameter magnifying lens –creating a ¼” diameter ‘spot’ of energy having a temperature of over 315 degrees C (600 degrees F).  This is sufficient energy to melt zinc.

All that’s required are a Fresnel lens, bright sunlight, and a means of holding a penny.  Actually, it is a bit more involved: the Fresnel lens must be positioned exactly perpendicular to both the sunlight and the penny; the penny must be of 1982 or later; and the penny must be supported by a thermally minimally-conductive means.

Guidelines for building the Atomic Penny Vaporizer are detailed in the book Physics Demonstration Apparatus.  This amazing book is available through Educational Innovations and includes ideas and construction details, including all equipment necessary, for the creation and use of a wide spectrum of awe inspiring physics demonstrations and laboratory equipment.  Included are 48 detailed sections describing hands-on apparatus illustrating mechanical, electrical, acoustical, thermal, optical, gravitational, and magnetic topics.  This book also includes sections on tips and hints, materials sources, and reproducible labels.

And, as a footnote, it is not illegal to ‘vaporize’ a penny or any other United States currency.  By law, it is only illegal to alter U. S. currency if the intent is to defraud – melting a penny with the Sun’s energy is simply a wonderful example of energy and its effects – perfectly legal.

Leave a Comment » | College Level, Energy, Experiments, High School Level, Middle School Level, Physics | Tagged: , , , , , , | Permalink
Posted by Tami O'Connor

The Energy Ball

December 30, 2009

by:  Sarah Brandt

This uniquely entertaining ball is a fun way to demonstrate open and closed circuits, as well for prompting discussions on conductivity. The following activities are perfect to use in elementary and middle school grades first exploring electricity and circuits.

When both sensors on the ball are touched and a complete circuit is formed, the ball flashes a red light and buzzes.

What makes the energy ball work?

Inside the energy ball is a simple circuit that is completely self-contained. By touching both sensors, the circuit is completed by electrons flowing through your body or another conductive material such as a paper clip. Materials that activate the energy ball are good conductors, meaning they pass electrons easily. Materials that do not activate the energy ball are poor conductors (or insulators), meaning they do not pass electrons easily. Your students will enjoy finding different ways to activate the ball:

One Student: Simply hold the ball so that both sensors are touched or, press one sensor with your hand and the other with a paperclip. Try experimenting with other materials (cardboard, plastic, metal) to see which will activate the ball.

Multiple Students: Using two students, have each student touch a sensor, and then hold hands with one another. See how many students can hold hands and still keep the energy ball buzzing. This is an easy way to demonstrate the difference between open and closed circuits – designate one student to be the “switch.” If the switch releases one or both of the hands they’re holding, the ball will stop flashing, representing an open circuit. Holding hands again will resume flashing, and the circuit will be closed.

An Entire Class: For a fun teaching game, try playing a variation of “Duck, Duck, Goose,” with the energy ball. First, form a circle of hands with the energy ball between two students.  One student should be outside the circle, who will be “it.” This student should then go around the circle, pointing to each person in turn and saying either “closed” or “open.” Once a person has been designated “open,” he or she should break the circuit and try to make it around the circle and complete the circuit before the person who was “it”.

Educational Innovations sells the Energy Ball (SS-30) for $3.95.

Leave a Comment » | Elementary Level, Energy, Experiments, Middle School Level | Tagged: , , | Permalink
Posted by Tami O'Connor

Teaching Energy Using Dropper Poppers

December 30, 2009

by: Tami O’Connor

One of the units I enjoyed most as a middle school teacher was the section on energy.  The many awesome hands-on experiments generated such a series of oohs and aahs that it made my already-enjoyable days even more enjoyable!  One of my favorites was a lesson that dealt with the Law of Conservation of Energy.  A consequence of this law is that energy cannot be created, nor can it be destroyed.  (The students would have already explored potential and kinetic energy before the following activity.)

I initiated this lesson reviewing what happens with energy in a closed system.  The students clearly remembered comparing the amount of potential energy to kinetic energy using the example that the height of a roller coaster’s first hill is always greater than the height of any of the remaining hills.  It is, of course, possible to have a little hill followed by a higher hill as long as the roller coaster is going faster at the top of the little hill than the next higher one.  The students were generally able to explain the transfer of energy including heat energy and sound energy in the overall system.

I would then take out a normal playground ball and a meter stick and ask the the students to predict the height the ball would bounce if dropped from a meter off the ground.  Most students accurately predicted that the ball would not bounce as high as the height at which it was initially dropped.  Of course, we would then test our hypothesis.  A few students in each class would always insist that the ball could bounce higher than the height at which it was dropped, so I would invite them to show me how it could happen.  Inevitably, the student would add energy to the system by throwing the ball down to the ground rather than simply dropping it.  This was a great opportunity for discussion and was a topic that we would tap into later in the lesson.

I would then pull out my complete collection of balls that ranged from the hard, less bouncy baseballs to the rubber and highly bouncy super balls and have the students explore on their own.  Though there were noticeable differences in the elasticity of the  balls in my collection, none of them bounced higher than the height at which they were dropped.

My next demonstration utilized a racquetball that I had cut in half… well, actually a little less than half.  I would again ask my students to predict how high the  half-ball would bounce.  The answers varied, but by this time, not one student predicted that it would bounce higher than its drop point.  As before, we tested their hypotheses before moving on to the next step.

Because the racquetball is very flexible, I was able to turn the half-ball inside out thus storing elastic potential energy.  Once again, I asked the students to predict what would happen when I dropped the ball.  Based on their recent experience, they all answered that the half-ball would bounce lower than its drop point.  Of course, because I stored elastic potential energy in this system, once the half-ball hit the ground, it popped right side out and was propelled significantly higher than the point at which it was dropped.  Talk about a discrepant event!

Thank goodness Educational Innovations sells Dropper Poppers.  This product eliminates the time and difficulty of cutting racquetballs in half, not to mention the expense of purchasing racquetballs really intended for use in the court!

Dropper Popper Activities

When this small, “half-ball” is turned inside out and then dropped onto a hard, flat surface, it releases the stored energy and “jumps” higher than the point from which it was released.

EXPLANATION
• Elastic potential energy is energy that is stored as a result of deformation of an elastic object such as a spring or a rubber band.
• Gravitational potential energy is energy that is stored as a result of an object’s position above the ground.

ACTIVITY #1 How High Will a Ball Bounce
Showing your students a regular ball such as a small super ball, basketball, or ping pong ball, survey the class to determine the height at which they predict the ball will bounce if dropped without additional energy. You may be surprised to learn that some students will predict that the ball will bounce higher than the point from which you drop it.

Drop the ball. Students will discover that the ball will never reach the height from which you dropped it. The Law of Conservation of Energy states that energy cannot be created nor destroyed; it can only be transferred as alternate forms of energy. The energy that initially went into the system was transferred out as sound energy and heat energy. The ball will never bounce higher than the initial drop point because the energy that comes out of a system can never exceed the energy that goes in.

Explain to your students that the ball’s energy was stored due to its position above the ground. Because of the force due to gravity, the ball falls down as it is attracted to the earth.

ACTIVITY #2 The Dropper Popper
Show your students the Dropper Popper (POP-100), and ask them to predict the height at which the popper will bounce if you drop it straight down. Drop the popper without turning it inside out and observe the height at which it returns.

Turn the Dropper Popper inside out and explain that by doing work on the popper you are storing energy in it. Have the class predict again the return height of the popper after it is dropped. Drop the popper with the “bulge” pointing upward. When the popper hits the ground the stored elastic energy will be released and will cause the popper to bounce higher than the point from which it was dropped.

ACTIVITY #3 Ping-Pong Ball – Be sure all students wear protective eye wear.
This activity is truly best when each student has his/her own Dropper Popper and a Ping-Pong Ball, (PNG-100). Have the students store energy in the popper by turning it inside out. Then place the ping-pong ball in the “bowl” of the popper. Drop the popper onto a hard surface in such a way that the ping-pong ball remains above the popper and inside of its “bowl”.  The bulge should be on the bottom of the popper so the ping-pong ball fits securely inside.  The height your ping-pong ball will fly will be truly impressive!
• Have students estimate how high the ball travels.
• Change the height at which you drop the popper and determine if the height the ping-pong ball travels is based more on gravitational or elastic potential energy.

An additional demonstration of the Law of Conservation of Momentum and Energy can be shown using the AstroBlaster (SS-150).  This device has several balls threaded on a plastic shaft.  When dropped straight downward onto a hard surface, the top ball can rebound to a height equal to five times the original drop!

4 Comments | Energy, Experiments, Middle School Level, Physics | Tagged: , , , | Permalink
Posted by Tami O'Connor

The Amazing Drinking Bird

December 1, 2009

by Tami O’Connor

Invented in 1945 by Miles Sullivan, the “drinking bird” has been a favorite of science teachers in every classroom from kindergarten through college. This amazing device is made of two glass bulbs (one representing the head and the other representing the body) joined by a glass tube (representing the neck).  Between the two bulbs, attached to the glass tube, is a metal fulcrum upon which the bird pivots.  The air has been removed from this closed device, and the bottom ball is filled with a colored liquid that has a high vapor pressure (methylene chloride). The rest of the bird’s body and head is filled with the vapor form of methylene chloride.

The demonstration is set up such that a glass, filled to the top with water, is placed in front of the drinking bird. The glass should be the same height as the pivot point of the bird. The bird’s head should be moistened and then the bird should be given a gentle push to begin it oscillating along the pivot point.  Eventually, the bird appears to drink repeatedly, on its own.  So, how does that happen??

The top bulb (head) of the drinking bird is covered with felt. After the felt is moistened with water and the water begins to evaporate, the temperature in the head decreases. This drop in temperature causes some of the vapor inside the head to condense, causing the pressure inside the birds head to decrease. The decrease in pressure in the top bulb causes the liquid from the bottom to be forced upward from the base. As the liquid flows into the top bulb, the bird’s center of gravity moves upward causing the bird to tip forward, dipping its beak into the glass of water.

After the bird tips over and is horizontal, the bottom portion of the glass tube is no longer in the liquid. The glass tube, now 90 degrees to the surface allows the vapor from the bottom to travel to the top until the pressure is equalized.  At the same time, liquid in the column flows back to the bottom bulb. The weight of the bird is now primarily below the pivot point, so the bird returns to a vertical position.

The liquid in the bottom bulb is now exposed to the temperature of the ambient air, which is slightly higher than that of the bird’s head. This cycle continues as long as there is enough water in the glass to moisten the felt on the bird’s head. This cycle gives the appearance of a bird drinking!

SUGGESTED CLASSROOM ACTIVITIES

I) Classroom Discussion

Q. Is this an example of perpetual motion?

A. No. The cycle repeats itself only as long as the water evaporates from the head

Q. What is needed in order for the Drinking Bird to work?

A. A difference in temperature between the head and body.

II) Student Challenges

  1. Observe the operation of the Drinking Bird and explain how it works.
  2. Discover a way to make the Drinking Bird cycle faster.
  3. Predict what will happen if a fan blows air toward the Drinking Bird. Does it make a difference which direction the air blows?
  4. Predict the result of using warmer or cooler water in the glass.
  5. How long will the bird cycle without needing a refill of the water in the open container? Can you find a way of causing the bird to cycle longer?
  6. Is there a difference in the cycle rate on a humid day vs. a dry day? Can the bird be used to determine the relative humidity in the air?
  7. Predict the result of placing a small inverted aquarium over the bird. Does this cause the bird to cycle more or less? (Note: as soon as the water in this closed system reaches its vapor pressure, water from the felt can no longer evaporate and the bird stops.)
  8. Can you attach a thread to the bird so that it does useful work, e.g. lifting a small paper clip?

Leave a Comment » | Chemistry, College Level, Elementary Level, Energy, Experiments, High School Level, Middle School Level, Physics | Tagged: , , , , | Permalink
Posted by Tami O'Connor

Chemistry of UV Detecting Beads

November 13, 2009

ronby: Ron Perkins

UV-sensitive beads contain pigments that change color when exposed to ultraviolet light from the sun or certain other UV sources. The electromagnetic radiation needed to affect change is between 360 and 300 nm in wavelength. This includes the high-energy part of UV Type A (400-320 nm) and the low energy part of UV Type B (320-280 nm). Long wave fluorescent type black lights work well; incandescent black lights and UV-C lamps will not change the color of the beads.

The dye molecules consist of two large, planar, conjugated systems that are orthogonal to one another. No resonance occurs between two orthogonal parts of a molecule. Imagine two planes at right angles to one another, connected by a carbon atom. When high energyuv651 UV light excites the central carbon atom, the two smaller planar conjugated parts form one large conjugated planar molecule. Initially neither of the two planar conjugated parts of the molecule is large enough to absorb visible light and the dye remains colorless. When excited with UV radiation, the resulting larger planar conjugated molecule absorbs certain wavelengths of visible light resulting in a color. The longer is the conjugated chain; the longer the wavelength of light absorbed by the molecule. By changing the size of the two conjugated sections of the molecule, different dye colors can be produced. Heat from the surroundings provides the activation energy needed to return the planar form of the molecule back to its lower energy orthogonal colorless structure.

Although UV light is needed to excite the molecule to form the high-energy planar structure, heat from the surroundings provides the activation energy to change the molecule back to its colorless structure. If colored beads are placed in liquid nitrogen, they will not have enough activation energy to return to the colorless form.

The UV detecting beads remain one of the least expensive qualitative UV detectors available today. They cycle back and forth thousands of times.

Leave a Comment » | Chemistry, Energy, High School Level | Tagged: , | Permalink
Posted by Tami O'Connor

Compressed Air as a Force

July 31, 2009

Normby: Norman Barstow

When the National Research Council produced the National Science Standards in 1995, they did so without including sets of lesson plans nor did they design them as part of a standard curriculum package. They were written to be used as goals for our students’ achievement in science.

In my classroom I always used the National Standards when designing my lessons, and they were always clearly represented in the objectives I set for my students. I have found that the topics of Force and Motion, as well as Air, (as part of a weather unit), can be easily taught using balloons to demonstrate the concepts of each. I have designed two different lesson activities that can be used to meet the following standards.

National Science Standards
Content Standards: K-4
Physical Science; Content Standards

  • An object’s motion can be described by tracing and measuring its position over time.
  • The position and motion of objects can be changed by pulling or pushing. The size of the change is related to the strength of the push or pull.

National Science Standards
Content Standards: 5-8

  • The motion of an object can be described by its position, direction of motion and speed.
  • An object that is not being subjected to a force will continue to move at a constant speed in a straight line.
  • If more than one force acts on an object along a straight line, then the forces will reinforce or cancel one another, depending on the their direction and magnitude. Unbalanced forces will cause changes in the speed or direction of an object’s motion.
  • Energy is transferred in many ways.

Balloon Rockets
In a recent workshop I attended, which presented a module on Air and Weather, ‘Balloon Rockets’ was an activity used to show that compressed air can exert pressure to propel a balloon rocket.

The activity used a straw threaded through fishing line, which was stretched across the room. A ziplock bag was then attached to the straw, and the inflated oblong balloons were launched by placing them into the open bag. The force produced by the balloon propelled the straw along the fishing line.

I noticed that the balloons tended to make the bag move from side to side, thus decreasing the distance traveled. We tried the activity again using balloons directly attached to the straw with masking tape. The oblong balloon traveled much farther than the ziplock bag attempt. Next, I introduced the Educational Innovations Rocket Balloons. BalloonOnALineWhat a difference, both in distance traveled and speed. The Rocket Balloons release the compressed air steadily from the opening of the balloon to the weighted tip thereby pushing the straw farther along the fishing line.

Balloon powered car

Another recent discovery I made in my basement was a compressed air (balloon powered) car that I saved from an NSTA workshop I had once attended. The ‘car’ was built with a piece of cardboard as the frame and an axle system made using a wooden skewer inside a drinking straw. The ‘wheels’ were bottle caps and the ‘engine’ was a straw with a balloon attached.

BalloonPoweredCar

While the oblong and/or round balloons worked fine, I wanted to try the EI Rocket Balloon. I had to modify the ‘car’ to account for the increased length and mass of theBalloonPoweredCar2 rocket balloon. The new chassis was now 4 X 14 inches, and I moved the wheels accordingly for this ‘super sized’ car. Again, the difference increased significantly in both distance and speed.

In addition to meeting the above National Standards, these are perfect experiments for elementary and middle school students on manipulating variables and testing hypotheses using the scientific method.

Leave a Comment » | Elementary Level, Energy, Experiments, Middle School Level, Physics | Tagged: , , , , , , | Permalink
Posted by Tami O'Connor

UV Radiation Activity

March 25, 2009

tamiby: Tami O’Connor

The sun is our primary source of ultraviolet radiation, however, there are a number of artificial sources of UV light including black lights, tanning beds and mercury vapor lamps. Ultraviolet radiation is usually considered to be a bad thing for very good reasons.

Generally speaking, there are three types of UV radiation here on Earth; UVA, UVB and UVC. Though the most destructive, UVC is almost never seen in nature because the earth’s atmosphere absorbs all of it. Though less destructive, overexposure to UVB can lead to all kinds of maladies including sunburn, some forms of skin cancer and cataracts.

UVA is the most common type of ultraviolet light found on Earth’s surface. It is responsible for the tanning effects of human skin and has the benefit of providing Vitamin D. However, overexposure to UVA can lead to toughening of the skin, suppression of the immune system and increased incidence of cataracts.

Unfortunately, UV radiation is invisible to the naked eye (unless, of course, you’re a honey bee…), so accidental overexposure to it is not uncommon. It is, however, essential to educate your students to the effects of this radiation as well as how to avoid overexposure.

There are a number of activities you can do in all classrooms from kindergarten through college with a plethora of materials including Ultraviolet Detecting Beads, UV Filters, UV Outside Detectors, UV Atmospheric Light Meters, and the like. One of my favorite activities to do in the upper elementary and middle school classroom is very easy and quite inexpensive. All you need is a piece of newspaper (with text), a plastic snack bag, sunscreen, black construction paper, tape, and a large poster board.

sunblockexperiment

Have each of your students cut a piece of newspaper to fit snugly inside a Ziploc snack bag. On each snack bag draw two lines with a marker dividing the bag into equal thirds from the top of the bag to the bottom. On the left hand third apply a thin coat of sunscreen (varying the SPF between students can yield interesting results). Cover the middle third with black construction paper. The right hand third should be left fully exposed.

Tape all the snack bags to a large piece of poster board such that none overlap any others. Bring the poster board with all the snack bags secured to it into the morning sunlight. Be sure to place the poster board in a place that it will be fully exposed to direct sunlight all day. At the end of the day bring the poster board inside, and the next morning, instruct your students to carefully remove their newsprint from the bags and record their observations.

Of course, there are other great experiments that can be found on our website, and if you have any ideas that we don’t, we would love to hear from you if you are interested in sharing… from your classroom to ours!

1 Comment | Biology, Chemistry, Earth Science, Elementary Level, Energy, Experiments, High School Level, Middle School Level | Tagged: , | Permalink
Posted by Tami O'Connor

« Previous Entries