College Level |

The Old Dog and the New Tricks

May 15, 2013

by: Ken Crawford

An amazing thing happened to me about 18 months ago…I learned something new! Now, I know that might not seem like a major thing…but for a person who has been a social studies teacher and administrator for 30 + years…I sometimes think that I have seen it all…nothing much new out there…but a single phone call changed all of that.

I received a call from a friend asking if I would be willing to meet with a gentleman who had invented a new teaching “tool”. He wanted to know if it would help teachers to be more effective in their classrooms. More effective teaching is something that I am always interested in…so I agreed to meet.

What I had a chance to see was a teaching tool called the PowerWheel. A micro hydro generator, it had the capability of using water from a sink to create enough electricity to light up a string of LED lights, charge up a cell phone or even power up a notepad.

Roy Bentley, the inventor/designer, asked me if I thought it might be something that teachers could use to help them teach students about energy. I remember telling him, “I’m a social studies teacher…we need to ask some science teachers”. I put together a focus group of teachers that represented grade levels from 3^rd grade through college. Some taught science all day long, others were expected to include science as part of their overall curriculum. We gathered them together in a room and just let them “play” with the PowerWheel. We had a great time, received some great feedback and saw what fantastic teaching ideas can be generated by a group of enthusiastic educators! I think I learned more about science in one day than I had in the past 20 years….it was amazing!

And for me, it was an eye opener. Science hadn’t been my strength in school, but here was a tool that was easy to use, easy to understand and even had me thinking about how I could use it in a classroom. The old dog was learning new tricks!

The PowerWheel has really taken off. It has been featured in a number of websites (including here at Educational Innovations) as well as been the hit of a number of conventions and gatherings of science teachers. Over the next few months, I look forward to sharing some great lessons on energy, and provide some great examples of how the PowerWheel is being used by other educators throughout the country. Stay tuned!

Ken Crawford first began teaching in 1975. He has been a teacher, coach and administrator at the junior high, high school and post-secondary levels. He continues to teach at the community college and university levels including supervision of student teachers interested in entering the profession. He also serves as the Director of Marketing and Learning Resources for RB Manufacturing-the producer of the PowerWheel

Leave a Comment » | Experiments, Elementary Level, Middle School Level, High School Level, College Level, Physics, Energy | Tagged: Green energy, renewable energy, PowerWheel, hydropower, micro hydro generator | Permalink
Posted by Tami O'Connor

Picture This!

January 10, 2013

by: Martin Sagendorf

It’s Easy:

To take neat photos of little things.

We Think:

That our digital cameras, web, and cell phone cameras can only take ‘life-size’ photos… but…

We’re Lucky:

These cameras can also photograph images provided by other optical devices…

Such As:

Microscopes and spectrographs.

Because:

These devices provide collimated images (i.e. focused at infinity) and an ordinary digital camera device can photograph these images.

The Images:

Are much smaller than ‘full frame’ – a photo-handling program is an absolute necessity – to enlarge and enhance the images. For the camera images shown, the camera used is a Panasonic DMC-TZ4.

For Example:

A slide-mounted hibiscus stem cross-section – through a 5X loupe.

This is the full image as it is captured by the camera:

The same image after partial cropping and enlarging:

And the same image after full crop and enlarging:

Three More Photos Of The Same Slide:

Through a 30X hand-held microscope:

Through a 30X single-eyepiece microscope:

Through one eyepiece of a Bausch & Lomb binocular microscope @ 19.5X:

And Another Slide:

A slide-mounted fish scale photographed through a 30X single-eyepiece microscope:

The same photograph enlarged even more:

Using A Web Cam:

Photo of a slide-mounted Aves Feather taken with an H.P. Webcam 3100 into a 30X microscope:

Through Spectroscopes Using A Camera:

Sunlight through a hand-held adjustable slit spectroscope:

An 18 Watt yellow Compact Florescent Lamp through a hand-held adjustable slit spectroscope:

Sunlight through a hand-held spectroscope with scale:

An 18 Watt bright white Compact Florescent Lamp through a hand-held spectroscope with scale:

It Takes Some Patience…

To align the camera to the device being used and to find the optimum exposure (light) level. Fortunately, using a digital camera allows one to immediately see the image and make adjustments if required. And using a small piece of black cardstock (with a ½” hole) will act as both a light block and protection for the camera and device lenses – sometimes it’s advantageous to tape the cardstock in place.

The Images On The Photos…

Will be quite small – a photo-handling computer program must be used to enlarge and enhance the images. Photoshop, or any of the many other image-handling routines will do this. The images in this blog were handled with Corel Paint ® Version 8 – it provides enlargement as well as changes of contrast and other photo characteristics.

Actually Doing It:

Cardstock piece:

Using a digital camera to photograph a slide-mounted object through a 5X loupe. An LED flashlight illuminates the white paper under the slide. Note that the slide is supported on two pieces of wood – this avoids a shadow of the object mounted on the slide:

A 30X hand-held microscope and digital camera:

Photographing through a 5X loupe with an iPhone:

A webcam shooting into a microscope’s eyepiece:

An iPhone taking a microscope photo:

A digital camera taking a ‘spectro’- photo:

And through an adjustable-slit spectroscope (note use of the cardstock piece):

Great for…

Individual or group investigative activities incorporating actual images either as single entities or as collages.

CAUTION !

Never point any optical device towards the sun!

Remember to:

Experiment for the best results – especially light levels.

Marty Sagendorf is a retired physicist and teacher; he is a firm believer in the value of hands-on experiences when learning physics. He authored the book Physics Demonstration Apparatus. This amazing book is available from Educational Innovations – it includes ideas and construction details for the creation and use of a wide spectrum of awe-inspiring physics demonstrations and laboratory equipment. Included are 49 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, High School Level, Physics | Tagged: digital camera, iPhone pictures, magnification, photography, spectroscope | Permalink
Posted by Tami O'Connor

Absorbent Spheres Help Students Soak Up Scientific Principles

March 14, 2012

by: John Fedors

GROWING SPHERES

Hydrophilic spheres from Educational Innovations offer a variety of interesting applications and opportunities for scientific inquiry. They come in a variety of sizes: small, regular, jumbo, & gigantic. For the following examples, I prefer the regular or #710 size. However, whichever size you choose, they will expand to about 300 times their original dehydrated size. As they absorb the water, they become almost invisible, due to having the same refractive index as water. When placed in de-mineralized or distilled water and kept away from sunlight, they will dehydrate to their original size and can be re-used. Dehydration time will depend on air humidity.

Once enlarged, these clear spheres can be used to demonstrate:

* The lens of an eye (such as those of a shark, calf or sheep) that has the ability to magnify the print on a page. A thin slice may be used to mimic a cornea transplant.

* The suspension of small items such as a coin.

* Roots of a germinating seed.

Enlarged growing spheres can also help to observe the relationship of Surface Area (A=4pr2) to Volume (V=4/3pr3) mass in grams. They can be used to graph relationships.

Using dark vegetable dyes you can also relate to why living cells need to divide. The ratio of surface area to cell volume does not permit timely diffusion of required metabolites in or out of the cell. This can be demonstrated by placing a dyed sphere in clear water for 10 minutes and measuring the clear area of the sphere in relation to the rest of darkened or dyed sphere.

My favorite though is the demonstration of cell organelles/microstructures in eukaryotic cells. In addition to the hydrophilic spheres, this demonstration requires serpent skin tubing. Serpent skin tubing is a crinkled cellulose dialysis tubing that stretches out, remains open and relatively sturdy. It eliminates the usual wetting difficulty in opening traditional dialysis tubing.

To demonstrate cell organelles/microstructures in eukaryotic cells you will need:

* Serpent Skin

* Small nut & bolt (to serve as weight)

* Twist Ties (used in grocery produce departments or with some trash bags)

* #710 Growing Spheres

* Tall glass

* Food Dye

* Distilled or de-mineralized water

Here’s what you do…

Take or cut a 6 to 8 inch length of Serpent Skin and flatten it. Fold it lengthwise 3 to 4 times, creating a long, narrow section. Fold the end up, then slide the folded end through the bolt. The bolt serves as a weight to keep the finished apparatus submerged in the dyed water. Use a twist tie between the bolt and then end of the tubing. I am a fan of the champagne twist – twist six times as you would see the wire is twisted on a champagne bottle top.

Place 25-35 Growing spheres through open end of the serpent skin and add 7-9 drops of dark vegetable dye to a tall glass. Add water to the glass up to an inch from the top or so. Place the weighted serpent skin with the growing spheres into the dyed water.

Results:

The dyed water will diffuse through serpent skin (cell membrane} and will cause the growing spheres to swell (this can take about 24 hours). The spheres will vary in size; larger spheres will collect towards the bottom of the glass while smaller spheres will collect towards the top. Adding more spheres initially will force them up and out. The varying sizes will help to visualize different organelles.

The dark stained organelles can be placed in clear colorless water for 5-10 minutes to demonstrate a colorless, clear outer surface area of diffusion. The spheres center will stay dark even after several water changes.

This also demonstrates the relationship of surface area to organelles volume and the need for the organelles to remain small for efficiency of passive diffusion.

Leave a Comment » | Biology, Chemistry, College Level, Elementary Level, Experiments, High School Level, Middle School Level | Tagged: dialysis tubing, hydrophilic, jelly spheres, organelles, osmosis, serpent skin tubing | Permalink
Posted by Tami O'Connor

Coupled Pendulums

December 2, 2011

by: Martin Sagendorf

One Pendulum…

Is interesting, but…

Two Pendulums…

Are much more interesting.

But Only If…

They are coupled together.

An Easy Way Is To…

Couple them at their pivot points. This is accomplished by hanging the two pendulums from a horizontal string.

There Are…

Many illustrations of coupled pendulums on the web; search for ‘coupled pendulums’ – but the fine points of making a really successful demo are rarely discussed… so before we start:

Some Guidelines:

- Make the pendulums absolutely identical: both the rod lengths and the mass values (the lengths are measured from the pivot points to the C.G. of the masses)

- Use rod lengths of at least 1/3 meter (13”) – so the pendulums don’t swing too quickly

- Use masses of at least 75 g (1 oz) – to provide a long swing time

- Space the vertical supports for a horizontal string length of 500 to 600 mm (20 to 24 in.) – weighted or clamped-down ring stands will work – and will work especially well if their top ends are joined by a solid bar to minimize vibrations

- The string should be fairly taunt – for example: a 13 to 15 mm (1/2 to 5/8 in.) droop in the center with two 75 g masses hanging 100 mm (4 in.) apart

- Use pendulum spacings of 75 to 125 mm (3 to 5 in.) – experiment for good results

- For the best results, symmetrical setup spacing is critical – try to achieve positions symmetric within 4 mm (1/8 in.)

- When pulling a pendulum to the side, two things are very important: first, don’t pull it too far (a mass rise of 75 mm (3 in.) is fine); second, the pendulum must be pulled at precisely a right-angle to the string

- For the following exercises, when two pendulums are raised, they should be raised to the same heights

With Two Identical Pendulums:

Center the two pendulums with the pair spaced about 100 mm (4 in.) apart

- (A.) Raise and release one pendulum

Question: What happens? Why?

- (B.) Raise (on opposite sides) and release both pendulums

Question: What happens? Why?

With Three Identical Pendulums:

Center the three with a space of about 75 mm (3 in.) between each

- (C.) Raise and release the center pendulum

Question: What happens? Why?

- (D.) Raise and release one of the outer pendulums

Question: What happens? Why?

- (E.) Raise (on the same side) and release both outer pendulums

Question: What happens? Why?

- (F.) Raise (on opposite sides) and release both outer pendulums

Question: What happens? Why?

So Far…

We have dealt with identical pendulums… but what happens if we:

- (G.) Make a pendulum with a greater mass (but the same length) and use it in place of one of those

above

Question: What happens? Why?

- (H.) Make a pendulum just slightly longer (say, 20%) than one of the three and use it in place of one of

the pendulums above

Questions: What happens? Why?

In Action:

Construction Notes:

- The horizontal string must be firmly attached (tied, hooked, or taped) to the vertical rods

- The pendulum rods are made from coat hanger wire or from welding rod

- Hooks are formed in the pendulum rods using a pair of pliers

- The masses can be any object that can be affixed to the rod – preferably an object through which a hole can be drilled and, for easy identification during demonstrations, the masses should be different colors

In This Apparatus:

- Length of horizontal string = 600 mm (23-1/2”)

- Length of pendulum rods (from inside hook to far end) = 440 mm (17-7/16”)

- Diameter and material of pendulum rods = 1/8” brass welding rod

- Thread on end of pendulum rod = 6-32 for a length of ¾ in. (Note 1)

- Nuts = brass 6-32 knurled (2 per rod)

- Small mass = 5/8” x 2-1/16” steel rod (75 g) – 3 required (Note 2)

- Large mass = 1” x 1-3/4” steel rod (175 g) – 1 required (Note 2)

- Distance from inside of pendulum rod hooks to the centers of masses = 400 mm (15-7/8”)

Note 1: A No. 6 screw diameter is 0.138”. – the 1/8 in. welding rod is 0.013” less – this is OK

Note 2: Drilled thru No. 29 (0.136”)

A Comment on Dimensions:

The overall dimensions are not critical, but the apparatus should be large enough to be easily viewed in a classroom setting.

A Definition:

These are ‘Simple Pendulums’ because they are not ‘ideal’: i.e. their masses are not concentrated at single points and the restoring force is not a constant – however they do exhibit ‘Simple Harmonic Motion’. This motion is an approximation at small angles – it is sufficiently accurate for our purposes.

And Further:

The details of Harmonic Motion and Simple Harmonic Motion are fascinating – the details of both can be found in any physics textbook.

‘Resonance’ is defined as the building up of large vibrations by the repeated application of small impulses whose frequency equals one of the natural frequencies of the body – in this case, a pendulum. Identical pendulums are required to provide maximum energy transfer. The mechanical energy is transferred by the ‘pulls’ on the supporting string – this is rather like a child’s swing where ‘pushes’ applied at the correct times will ‘add’ and act to increase the swing amplitude.

In Summary:

These demonstrations provide vivid illustrations of energy transfer between two and three resonant bodies. Even better, additional pendulums, various masses, and variations of excitation will provide more interesting demonstrations and bases for experimentation.

Marty Sagendorf is a retired physicist and teacher; he is a firm believer in the value of hands-on experiences when learning physics. He authored the book Physics Demonstration Apparatus. This amazing book is available from Educational Innovations, Inc. – it includes ideas and construction details for the creation and use of a wide spectrum of awe-inspiring physics demonstrations and laboratory equipment. Included are 49 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.

4 Comments | College Level, Energy, Experiments, High School Level, Middle School Level, Physics | Tagged: coupled pendulums, energy, harmonic motion, momentum, pendulums, Physics, resonance | Permalink
Posted by Tami O'Connor

Make Your Own Time

October 10, 2011

by: Martin Sagendorf

A Definition:

Clocks measure time – it can be a continuous measure of events passing or the measure of the interval between two events.

Of Hours:

After years of evolution, our modern clocks now divide the day into 24 equal length hours. And, as we know, there are two systems in use today: Americans use the “double-twelve” system while the rest of the world uses the 24 hour system.

As An Aside:

The word “hour’ comes from the Latin and Greek words meaning season, or time of day. A “minute” from the medieval Latin pars minuta prima (first minute or small part), originally described the one-sixtieth of a unit in the Babylonian system of sexagesimal fractions. And “second” from partes minutae secundae, was a further subdivision on the base of sixty – i.e. “a second minute”. (ref. Pg. 42 The Discoverers by Daniel J. Boorstin)

The “Double-Twelve” Clock Face:

Has 12 at the top – probably because at noon the sun is at its highest point in the sky.

But…

We can make a clock with 12 o’clock anywhere we wish and the clock will still work just fine.

Here we have a clock with 12:00 where 5:00 usually is. Now, if the hour hand points to 12 and the minute hand points to 2, the time would be 10 minutes past 12.

Or:

We can rearrange the face:

Or:

We can replace the numbers:

Or:

We can divide the day into ten hours (times 2).

Suitable Clocks & How:

- Good candidates are battery operated clocks with face diameters of 8 inches or less.

- There are a variety of these clocks – all I’ve seen can be disassembled if one is careful. When a front cover face must be removed, it is usually secured by three small tabs at the inner part of the face – use a worn common screwdriver to gently pry inwards, over a tab location, between the side of the cover face and the clock body – this will release the tab and allow the cover face to be gently ‘worked’ outwards. Other clock designs are held together by multiple screws from the rear – be careful, some of these have real glass for the cover face.

- The hands can be pried-off by using one’s fingernails on opposite sides of the hub of each hand.

- A new dial face should be of ‘card stock’ (8-1/2” x 11” is readily available) – standard weight paper is too light.

- A dial face must be a little smaller (1/16” on the diameter) than the opening into which it is placed – this will prevent buckling from expansion due to high humidity.

- The dial face can be hand-drawn or computer-generated (using any of the popular computer drawing programs).

- A punch or a craft knife can be used to cut out the center hole.

- Sometimes the original dial face can be removed – sometimes not – it is not really necessary. In either case, multiple small pieces of double-sided tape are used to fasten the new dial face.

- When reinstalling the hands, they must be synchronized – the easiest way to do this is to set (press on) all the hands pointing to the (original) 12:00 position.

And More:

Over the years I, and my students, have made dozens of different clock faces – there seems to be never-ending variations. You, and your students, will think of many different ones – just think of anything that represents numbers. And, what’s neat is that each individual clock can have the maker’s name and/or school name included on its face.

Leave a Comment » | Chemistry, College Level, Elementary Level, High School Level, Middle School Level, Physics | Tagged: Clock making, interesting clock | Permalink
Posted by Tami O'Connor

The Tipping Point

October 6, 2011

by: Ron Perkins

The bottle balancer is a fascinating conversation piece that illustrates the principle of center of gravity! A small hole in an oak board allows you to balance a 2-liter soda bottle at an angle that appears to defy gravity. This can be used as a teaching tool or a centerpiece at your next party! Hold the special angle cut of the wooden, bottle balancer board against a flat horizontal surface. When a full, sealed, 2-Liter soda bottle is inserted into the wooden hole from above, it will catch the bottle flange and the wood/bottle assembly balances at a surprising angle.

Explanation:

In order for an object at rest to NOT tip over, its center of gravity, or its center of mass must be directly over its base. A goose-necked desk lamp is usually quite stable, unless it is configured so that the lamp part is stretched horizontally, far from the large base. Then, it becomes less stable and often tips over. The wood/bottle assembly example is more complicated than the lamp example because if the bottle is moved, the flowing liquid results in a change of its center of mass.

Consider a thought experiment! To simplify the Soda Bottle Balance, consider the soda in the bottle frozen and the bottle super-glued to the wooden board so that everything balances on the angled edge of the board. Balancing will only occur if the center of mass is directly above the flat angled edge of the wood. How do you find the center of mass? Loosely tie a string to your forefinger with a hanging weight tied to the other end of the string, e.g. a large metal nut or a bunch of washers. Balance the object (in this case, the glued and frozen bottle balancer) on your forefinger above the string. The center of mass will be somewhere along the straight line that includes the string. Then, balance the wood/bottle assembly on your forefinger at a different point. Again, the center of mass will be somewhere along the straight line that includes the string. Where the two lines intersect is the center of mass. This imaginary point must be directly above the object’s base in order for the object to be stable and not tip over. Sometimes the center of mass is within the object and sometimes it is a point in space outside the object, as in the wood/bottle assembly.

What happens when you release the carbon dioxide gas from a balanced 2-liter soda bottle? A sealed 2-liter soda bottle has a mass of more than 2000 grams of material and contains about 10 grams of carbon dioxide under pressure (Wikipedia). If the bottle is opened and the gas released, the mass of the bottle becomes less by about 0.5%. However, approximately half of this decrease in mass is to the left of the center of mass and half to the right. The release of gas results in very little change in the center of mass. In trying the experiment, one must find a method of slowly releasing the gas in the bottle without disturbing its balance. One method would be to make an extremely small hole in the balanced bottle by pressing a small hot needle into the bottle, allowing gas to slowly escape without losing liquid. This way the bottle assembly stays balanced as the gas begins to slowly leak from the bottle. Observe what occurs! Sounds like an interesting experiment! Please let Educational Innovations know the results!

Note:

As the pressure is released, the bottle may sag causing the soda to flow, drastically changing the center of mass of the bottle. Also, if the gas is released too quickly, foaming will occur as dissolved gas quickly comes out of solution, resulting in loss of liquid.

Leave a Comment » | College Level, Elementary Level, Experiments, High School Level, Middle School Level, Physics | Tagged: Balance, Center of Gravity, Center of Mass, Illusion | Permalink
Posted by Tami O'Connor

The Law of Dulong and Petit

September 3, 2011

by: Dr. Jean Oostens

Atoms were proposed in antiquity without any experimental evidence by Democritus, a Philosopher. This must have been a problem for Newton and Leibnitz who posited that there was always a mean of considering smaller and smaller intervals of space to calculate the “instantaneous velocity”.

The introduction of the precision balance in chemistry by Lavoisier paved the way for Dalton to formulate his laws on the “definite and multiple proportions” governing chemical reactions. This supported the atomic theory, without giving it general acceptance.

Specific heat was defined as the quantity of heat needed to increase one gram of a substance by one degree. There was no definite pattern when specific heats of various substances were compared. Until two French scientists, Dulong and Petit in 1819 calculated specific heat by atomic mass. There appeared a number of cases where the results were quite similar: about 6 calorie per mole. This was equivalent to stating that any atom is as good as any other to store heat! This was a small step towards acceptance of the existence of atoms. An explanation for this, and the reason for the exceptions, had to wait the early 20th century explanation by Albert Einstein. By that time, atoms had gained wide acceptance from the work of Rutherford, and soon by Bohr.
—————————————————————————————————————

The Lesson:

You are given several chunks of metal, each containing 0.6 1024 atoms (i.e. one mole) of one element. How will each of those samples, when dropped in a standard quantity of hot water (typically 200 mL and 70 C) affect the temperature?

Step 1 Use a good balance (at least 0.1 gm resolution) to determine which element you are dealing with. If possible confirm your identification with an additional cue.

Step 2 . Select one of the computers available, and look at the readings of the two temperature probes (lower left corner of the screen). They will tell which pair of element your are assigned to investigate.

Step 3. Prepare your two standardized water containers. Fill the two Styrofoam cups with equal amount of tap water. Check that the two temperature sensors read the same within 0.1 C. Then bring the two cups to the microwave oven and heat for 2 minutes. Exchange the positions of the cups in the microwave oven and repeat another 2 minutes of heating (this will uniformize the temperatures).

Carefully bring back the two cups (the water may be very hot) to your station and insert the temperature probes into their respective cup. You need to note which cup is to receive the required element (Gold => Yellow and Silver => Grey for example). When the probes reach an equilibrium, after 5 to10 seconds, verify that the two temperatures match within a degree or less. If necessary, use a 60 mL syringe to transfer water from one cup to the other and then the other way. The idea is to have the same quantity of water at the same temperature within reason.

Step 4. Start the measurement. Hit the “START” button with the mouse and wait 10 to 15 seconds during which an horizontal line should appear, with both traces nearly on top of each other (if this is not so, go ahead anyway: you can always get another chance).

Drop your two samples the same time, one in each cup and watch until the completion of the three minutes.

Compare your results with the other teams’ and draw conclusions of the exercise.

This experiment on Dulong and Petit Law was performed by the students of Professor Shuffett’s Chemistry class at Lindsey Wilson College (Columbia, KY). It uses the mole set from Educational Innovations and takes advantage of existing data acquisition capabilities at that college.

About the Author: After 20 years of research in Particle and Nuclear Physics, Dr. Oostens included in his activities, teaching at several college and universities all over the US. After moving to Kentucky 17 years ago, he co-founded a local Alliance, STASCKY (Science Teachers Alliance – South Central Kentucky). He hasserved as STASCKY’s secretary since its inception.

For more than forty years he has kept a small research activity in collaboration with Los Alamos National Laboratory in New Mexico. His involvement there started when Dr. Louis Rosen started a non-programmatic (i.e. not defense) group to attract more talents from all over the world. In 1970, he invited Dr. Oostens to participate in that project as the first non-American to work there. Dr. Louis’ idea was predicated on a high intensity 800 MeV accelerator called LAMPF (for Los Alamos Meson Proton Facility). Later on, the proton beam was used to create a flexible neutron source, LANSCE, that attracted a variety of researchers from all fields.

1 Comment | Chemistry, College Level, Experiments, High School Level, Physics | Tagged: Chemistry, Dulong and Petit Law, metals, mole, Specific heat | Permalink
Posted by Tami O'Connor

Invite Newton Into Your Classroom

May 28, 2011

by: Matthew Morris

Newton was a revolutionary thinker of his time. He is responsible for the three laws of motion that we still use today;

1. Objects that are not in motion remain stationary unless acted upon by another force.

2. There is a direct relationship between the force acted upon the object and the mass of that object times the acceleration the object feels (F=ma).

3. For every action there is an equal and opposite reaction.

Nobody before Newton could explain why objects acted the way they did, but with these three laws he quantified movement in terms everyone could understand.

But there was a problem with his theory; if all motion had to be caused by some force acting on it, then why do objects fall towards the earth when you release them from a fixed position? This free falling object was in fact free, meaning free of outside forces acting upon it (besides wind resistance). There were no visible forces acting upon that object. So why do they move downward if nothing is acting on it? But Newton explained this motion with gravity. He said that gravity is a force that the earth has upon all objects, something invisible that pulls us down at all times at a constant acceleration. There is a myth that the way Newton thought of the idea of gravity was when he was thinking about it under an apple tree when an apple fell on Newton’s head and at that moment, he figured out that there must be a force pulling the object down. This is also why apples are used to demonstrate Newton’s force, but no one knows definitively if the myth is true or not.

At the time Newton didn’t know that the acceleration of Earth’s gravity would later be calculated at approximately 9.81 m/s². Also, at the time, he couldn’t explain what this force was made of, but only that it was invincible and constant. It was many years later that Einstein explained gravity with the theory of relativity stating that space and time were really one thing called spacetime, that bound all objects together like a web such that when an object has mass, it stretches the spacetime causing objects around it to feel a ‘pull’ towards the center object. Also Einstein discovered that this force increases as the outer object gets closer to the center object. Think of it like a blanket being stretched really thin and a ball being placed in the center and another ball being rolled across the blanket from one side to the other. This would cause the one moving ball to move towards the ball in the center because of the bend in the blanket, or spacetime.

So, looking back at Newton and the apple, the earth’s mass causes a big bend in spacetime, which causes other objects, such as apples, to be pulled downward at all times, even when they are on the ground already. Hey, something has got to keep them from floating upward.

Now that we’ve explained the motion, let’s define it in equations so that we can predict how the object will act during a free falling motion. The first and most important thing to remember about free falling objects is that the mass doesn’t matter. A bowling ball and a pencil will fall, or accelerate at the same rate towards the earth. Meaning if you go on the roof of your building and drop a bowling ball and a pencil off of it at the same time, they will hit the earth at the same time. But someone might say, “What about a feather? It won’t fall at the same speed as a bowling ball.” And they would be right. But what they are forgetting is air resistance. The bowling ball has very little air resistance because it is very aerodynamic, but the feather is not very aerodynamic. If you were to repeat this test in a vacuum then the resistance due to air (drag) would be removed as a factor, and the objects would fall at the same speed and hit the ground at the same time.

So back to the equations; Using calculus, we can start with the equation for the acceleration of gravity and integrate an equation to define the velocity of the object and then integrate it again to find the position of the object. If we define x as time measured in seconds, then the equation for the acceleration of the object looks like this A(x) = 9.81. One might notice that there is no x in the actual equation and this is because no matter how long the object is falling, the acceleration of the object at any time will always be 9.81 m/s². So by integrating that function of x, we get V(x) = 9.81x + C. In this case, we are defining the velocity of the object in a function of time. C represents any starting velocity of the object, such as if the object was thrown downward. This can also be defined as V₀, or initial velocity. Then if we integrate that function again we get a position function that looks like this, S(x) = 4.905x² + Cx + K. In this last equation, K represents an initial position, such as if you defined the height of the object being 10 meters above the starting point, then K = 10. And C still represents the initial velocity.

From these equations, we can know that, if we eliminate the wind resistance, any object, the free falls for 1 second will have an acceleration of 9.81 m/s², a velocity of 9.81 m/s, and a position of 4.905 m. After 2 seconds it will have an acceleration of 9.81 m/s², a velocity f 19.62 m/s, and a position of 19.62 m. And at 3 seconds, an acceleration of 9.81 m/s², a velocity of 29.43 m/s, and a position of 44.145 m. You can predict all of these values at any time using these equations just by plugging in the number of seconds into x.

Keep in mind that all of these equations are generalizations of free falling objects. Certain objects, in real life, because of wind resistance, will fall at different rates. Also, due to wind resistance objects will reach something called terminal velocity where the velocity cannot go any higher because the wind speed it feels restricts any increase in velocity. For humans, the terminal velocity is typically around 54 m/s or about 120 mph. For a raindrop it is around 25 m/s. Also, the earth’s gravity, though seemingly constant, isn’t actually constant. It has very miniscule changes as you change locations on the earth’s surface due to the density of the Earth at that spot. But these changes are so small students shouldn’t even bother trying to account for them.

So, what is a Newton anyway? It is the force created by the weight of an average apple (mass of approximately 102g). Technically speaking, a Newton is the force required to accelerate a mass of 1 kilogram at a rate of 1 Meter per second per second. What better way for your students to visually understand Sir Isaac Newton’s idea of F=ma, than to drop a 1 Newton foam apple onto someone’s head? They will remember it forever! Educational Innovations sells The Newton Apple as singles and in a five pack. The five pack includes a full Starter Guide, which includes experiments to conduct using the Newtown Apple, information about Sir Isaac Newton, and information about the Newton as a unit.

Experiments For Your Students:

Elementary/ Middle School Students

1. Have students hold their hand straight out. Ask them to describe what they feel on their hand. Then place the Newton’s Apple on their hand. Ask them to describe what they feel on their hand now. Ask them what they think will happen if another apple is added to their hand. Ask them to explain why this is the case.

2. Take a Newton’s Apple and a pencil or another small object and weight each object so the students can see the difference in weights. Ask them to predict what would happen if you dropped the objects from the same height at the same time (i.e. which would hit the ground first?). Have a student release the objects at the same time from the same height. Ask the students to describe what happens. Try to relay the concept that the mass of the objects didn’t really matter because no matter what they weigh, the objects will still fall at the same speed and hit the ground at the same time.

3. Repeat the same experiment as before but use something with a lot of air resistance, such as a piece of paper. Then crumble the paper up into a ball and drop both objects again. This time explain to the students that because the paper had a lot of air resistance before, it took longer, but then when it was made in a ball, the paper was still the same weight but now less air resistant.

High School Students

1. Take a block of wood and tie it to a piece of string. Then tie the other end of the string to the Newton’s Apple. Put the block of wood on a table and then hang the Newton’s Apple over the edge. Make the table surface smooth enough that the block will slide, but not too fast. This experiment is to demonstrate friction between two surfaces and how it would affect the almost free falling object. Place the block on a table with a different surface (one that is less smooth). Notice the difference.

2. Attach a spring to a pole or hanger such that the spring can dangle freely. Then attach the Newton’s Apple to the other end of the spring. Pull down the Newton’s Apple so that when you release the Newton’s Apple it will move up and down in a continuous pendulum-like motion. Ask the students to describe the motion and to predict what would happen if you double the weight at the end of the spring. Add a second Newton’s Apple to the end of the spring and repeat the motion of the spring by pulling down the Newton’s Apples the same distance as before.

Leave a Comment » | College Level, Elementary Level, Experiments, High School Level, Middle School Level, Physics | Tagged: acceleration, awesome experiment, force and motion, gravity, Newton's Apple, Sir Isaac Newton, spacetime | Permalink
Posted by Tami O'Connor

Silicon from Sand

March 2, 2011

by: Carl Ahlers

Next time you step onto the beach, bend down, grab a handful of sand and admire the fact: By mass 47% of what you hold in your hand is the element silicon. The rest is simply oxygen. Remarkable!

Silicon is the second most abundant element in the earth’s crust (27.7%) – only oxygen beats it – and can easily be extracted from white sand (SiO₂) in a spectacular reaction in the school science laboratory.

Thermite Reactions

In Thermite reactions metal oxides react with aluminum to produce the molten metal. These redox reactions require substantial activation energy to get going and are highly exothermic.

They have been used industrially for welding (even under water), the preparation of metals from their oxides (reduction) and the production of incendiary devices. The process is initiated by heat but then becomes self-sustaining.

In the early 1900’s a product called Thermit^® was developed and used worldwide to weld rail tracks. The photo (taken by J J Szerkeszto) was taken in 2010 proving that it is still in use today. This is the reaction:

Fe₂O₃ + 2Al → 2Fe + Al₂O₃+ energy

The question is: Can silicon be persuaded to give up its oxygen in a similar thermite process?

For Fe₂O₃, ∆H_f = -822 kJ/mole; for SiO₂ , ∆H_f = – 859 kJ/mole

In 1902, Kuhn described a method that is a variation of the thermite reaction for the reduction of silicon from silicon oxide. In this process a primary reaction provides the activation energy to initiate the secondary reduction reaction.

Extracting Silicon from Sand

Safety / Risk Assessment

★ Burning magnesium produces bright light that may cause temporary loss of sight. Avoid looking directly at the flare.

★ Magnesium is very reactive and contact with other chemicals may result in explosion.

★ This demonstration produces intense heat and molten silicon. A dry-powder fire extinguisher should be readily available at all times. DO NOT use water as an extinguisher as this will produce potentially explosive hydrogen gas.

★ The near-impossibility of smothering and the high temperatures generated make thermite reactions potentially hazardous. Appropriate precautions must be taken before thermite is ignited. Keep all flammable material away from the area.

★ The reaction should be performed in a fume cupboard or outdoors behind a safety shield as it produces intense heat, smoke and molten metal. Sparks can fly up to 2 m horizontally.

★ Wear heat-protective welding gloves and use metal tongs to handle the fragments of the clay pot and molten silicon after the reaction has taken place.

★ Wear protective clothing and safety glasses.

Chemical Safety

Aluminum (Al)

Risk phrases: R10 – 15 Extremely flammable; Contact with water liberates highly flammable gases.

Safety phrase: S7/8/44 Keep container tightly closed; Keep container dry.

Magnesium (Mg)

Risk phrases: R11-15 Extremely flammable; Contact with water liberates highly flammable gases.

Safety phrase: S7/8-43 Keep container tightly closed; Keep container dry.

Hydrochloric Acid (HCl) is a strong acid. Treat with the greatest respect.

Risk phrases: R34-37 Causes severe burns; Irritating to eyes & respiratory system.

Safety phrase: S2-26 Keep out of reach of children; In case of contact with eyes, rinse immediately with plenty of water and seek medical advice; Wear suitable gloves and eye/face protection.

Sodium hydroxide (NaOH) destroys clothes and causes injury to the skin. Treat with the greatest respect.

Risk phrases: R35 Causes severe burns

Safety phrase: S2/26/37/39 Keep out of reach of children; In case of contact with eyes, rinse immediately with plenty of water and seek medical advice; Wear suitable gloves and eye/face protection.

What You Will Need

Chemicals

• Aluminum powder, 325 mesh or finer

• Powdered sulfur

• Dry white sand – beach sand or washed white builder’s sand

• Hydrochloric acid, 4M (add 180 mL conc. HCl to 500 mL water)

Initiator chemicals:

• Fine magnesium powder & magnesium ribbon (5 cm) or Potassium permanganate (KMnO₄) and glycerine

Other

• Mortar & pestle

• Small clay flower pot, ∼ 6.5 cm (2.5”) inside top diameter

• Small glass beaker & plastic container

• Electronic balance, 100 g ± 0.1 g

• Heat resistant pad

• Transparent safety shield or fume cupboard

• Heat-protective gloves eg. welding gloves

• Spatula & metal tongs

• Fire lighter with long stem

Here’s How

1. Dry about 50 g of sand in an oven for 2 hours (∼ 350℉) and then grind the sand to a powdered form in a mortar and pestle.

2. Weigh and mix the following to form a homogenous mix:

8 g of dry aluminum powder

10 g of powdered sulfur

7 g of dry powdered sand

3. The best mix is obtained by shaking the mixture for a minute in a sealed plastic container. Do NOT grind them together in a mortar and pestle.

4. Use the small clay flower pot. If it has a hole in the bottom – cover the hole with paper. Transfer all of the mix to the pot.

5. Make a small cone-shaped indentation at the top (¾” deep and ¾” wide) and fill this with magnesium powder to facilitate ignition. (For an alternative method see Note 1 in the book). Fray a 5 cm (2”) magnesium ribbon’s end with scissors. This will enlarge its surface area and aid ignition. Push this fuse into the magnesium powder pile.

Safety: Position the pot on a heat resistant pad in a fume cupboard or outdoors away from any combustible material. Use a safety shield. Wear protective eye wear, gloves and a lab coat.

Light the frayed end of the magnesium ribbon using a long stemmed fire lighter. It may take a few seconds before the ribbon starts burning. Once this happens – step back immediately. Ignition of the mixture is not instantaneous and might take as long as 60 seconds. The reaction will produce lots of spattering, bright light and intense heat. The temperature is reported to be well above 2,200℃ (4,000℉). The residue will have an orange-red glow and be hot for some time. If required, carefully pick up the red-hot residue using metal tongs.

If the reaction fails to react: Wait 3 minutes. Do not approach the reaction vessel until you are sure ignition is not possible. Replace the ribbon or add more magnesium powder. Try again.

7. Purify the silicon residue.

Leave the clay pot to cool for 20 minutes. Break the pot apart and separate the silicon residue from the clay pieces. Break the residue into smaller pieces using light taps from a hammer.

8. The silicon (Si) and aluminum oxide (Al₂O₃) is now separated from the aluminum sulphide (Al₂S₃) by adding the residue to diluted hydrochloric acid in a glass beaker (acid – take care!). Copious amounts of hydrogen sulphide will be evolved – foul smelling rotten egg gas – use a fume cupboard or perform outside.

Al₂S₃ + 6HCl → 2AlCl₃ + 3H₂S

Leave the residue in the acid until gas formation subsides. This process may take up to 20 minutes. The finer the residue, the faster this reaction.

9. Now, carefully discard the acid under running water and wash the residue in the beaker for 30 seconds. The silicon will be found in the form of pea-size, hard, black, crystalline globules. It is insoluble in most acids. Boil the globules in a glass beaker using dilute hydrochloric acid for further purification.

Disposal

Allow the solids and clay fragments to cool to room temperature. The clay flower pot invariably cracks and should not be re-used. Dispose of all solids in the waste bin.

The Chemistry

There are basically three reactions here that produce a chain reaction effect. Magnesium burns in oxygen and produces the activation energy to get the sulfur and aluminum going.

2Mg + O₂ → 2MgO + energy

The aluminum and sulfur again, react in an exothermic reaction that is the source of activation energy for the silica and aluminum.

2Al + 3S → Al₂S₃ + energy

3SiO₂ + 4Al → 2Al₂O₃ + 3Si + energy

In the book “Expose, Excite, Ignite!” the author describes two simple tests that can be performed in the school lab to establish if the globules are indeed the semi-conductor, silicon. You can purchase this book from Educational Innovations at http://www.teachersource.com.

1 Comment | Chemistry, College Level, Experiments, High School Level | Tagged: Silicon, thermite reactions | Permalink
Posted by Tami O'Connor

Phenomenon Of The Disappearing Dot! – Is it Physics, or Math, or Perception?

February 9, 2011

by: Lee Walker and Partnership for Learning.com, LLC

Use a hack saw to cut a 2¼ to 2½ inch length of ¾ inch outside diameter PVC pipe. The point is for the tube to be three times the length of its diameter. While 2¼ inches is more precise, it is fine to fudge just an extra ¼ inch. Trust me, it’s close enough. Next put a green dot at one end and a red dot on the other (see photo). I like to drill two small depressions and put the paint in those two shallow holes (don’t drill through).

Set the cylinder down in front of you on a nice smooth surface. You will need plenty of room as you develop the operational skills, so a reasonably smooth desk or table top should be fine.

Now, place the tip of your index finger on the red dot. It works just fine on the green one, but let’s have the first run match the photographs. If you force down your finger as you pull it slightly back toward you, the cylinder will spin rapidly around a horizontal axis in your direction. You can visualize the action around this axis by imagining the cylinder seen from one end so that it would look like a spinning wheel.

The two drawings below show how the cylinder, viewed from the end, rolls (spins) around a horizontal axis in a direction toward the finger that snaps downward (though sliding away at the same time). As this is going on, (see the drawing on the left) the end that had the fingertip on it, rotates around a vertical axis in a direction away from the fingertip.

At the same time that the view of the red dot end of the cylinder may be thought of as a wheel spinning around a horizontal axis toward you, the whole cylinder will spin around a vertical axis and skitter away from you. The spin around the vertical axis (seen from above) is shown in this photograph just after my finger popped downward to the table top.

O.K. Here’s the fun part. As the cylinder settles into a stable, whirling action, you will see three of the red dots appearing. If connected the dots would be at the vertices of a triangle. Notice that the green dots do not appear at all. Now, try repeating the whole thing but push down on the green dot. When the action is stabilized only three green dots will show up at the vertices of our imaginary triangle. Pretty neat, isn’t it?

Here are some tips to help investigate what is perhaps going on. When you have spun the cylinder, it has skittered out away from your hand, and settled into a stable, high speed spin, you have probably noticed that there seems to be an illusion of a round, rather ball-shaped zone in the middle of the blurry spin. This illustration (obviously touched up with the red dots) presents a view of that ball region viewed from overhead as the cylinder spins on a smooth table top.

When your cylinder is doing this try observing from the side with your eye down at the level of the table. One end of the cylinder is in contact with the table during the high speed rotation around the vertical axis and the other end is not in contact with the table’s surface.

The drawing on the left is my attempt to show the cylinder running with one rim in contact with the table and the other end slightly elevated. As this occurs, you can see that the white cylinder is in many places, but the central part of the spin is routinely occupied by white PVC. Does this help you get an idea about that ball-shaped central part? There may even be some accounting for speed differential if the part in contact with the table makes a longer circuit than the up end for each spin about the vertical axis. Hmmmm.

Now, this next part is almost as strange as any of the above, and probably no one of the matters I’m going over works alone to present the phenomena that make the spinning cylinder so much fun.

The idea here is that the end with the red dot (the finger just rolled it) is turning around the horizontal axis toward the launch person (see the little blue arrow in the tube), BUT the cylinder at that end is spinning away from the person around the vertical axis (see yellow arrow). The speed of those two actions work against each other (are subtractive). The red arrow shows that the other end is turning around the horizontal axis toward the person, AND that end is also turning around the vertical axis toward the person (see green arrow). Those two speeds are additive.

Speed of motion and perception must be linked. After all, things that go rapidly past the eye may be blurred or barely visible at all, while things that are stationary or slow moving may be seen quite clearly. Is it a coincidence that one dot is gone and one is seen THREE times when we use a cylinder that is three times as long as its diameter?

Just for fun, here is one more bit. The circumference of a tube may be found by multiplying its diameter times pi (3.141 will do for our purposes) . Now the relationship of the diameter to length may be made quite interesting by thinking, “ Does the tube roll completely around the horizontal axis three times to make one rotation around the vertical axis?” Some experimenting could be very beneficial. Still using a tube of the same diameter with the same placement of red and green dots, what would happen if that tube were only twice as long as the diameter? How about four times as long?

Enjoy the PHENOMENON OF THE DISAPPEARING DOT! Have fun exploring and using your creativity! Please contact lee@partnershipforlearning.com if you think you make a breakthrough. Lots of what I’ve read about this doesn’t really satisfy my curiosity.

Educational Innovations carries the Physics Quest 2010 Kit – Spectra’s Force, which includes the materials for this experiment as well as 3 other experiments.

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

The Old Dog and the New Tricks

Picture This!

It Takes Some Patience…

The Images On The Photos…

Actually Doing It:

Great for…

CAUTION !

Absorbent Spheres Help Students Soak Up Scientific Principles

GROWING SPHERES

Here’s what you do…

Coupled Pendulums

Make Your Own Time

The Tipping Point

The Law of Dulong and Petit

Invite Newton Into Your Classroom

Experiments For Your Students:

Silicon from Sand

Extracting Silicon from Sand

Safety / Risk Assessment

Chemical Safety

What You Will Need

Disposal

Phenomenon Of The Disappearing Dot! – Is it Physics, or Math, or Perception?

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