## 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…

## Seeing a Magnetic Field in 3-D

June 12, 2010

by: Martin Sagendorf

This is actually quite easy to do.  This clearly illustrates that magnetic fields are not flat (as too frequently demonstrated in the classroom).

This easy-to-make construction requires only four components:

1. A clear plastic bottle (about 1-3/4” in one dimension) – the one illustrated below is a 12.6 fl oz ultra concentrated Joy ® dishwashing soap bottle – Note that any bottle originally containing soap or detergent will require repeated rinses to completely remove all of its original contents.
2. Six 17 mm x 3 mm Neodymium ring magnets
3. A very small quantity of fine iron filings
4. 2 lengths of ¾” x 3” clear tape (clear ‘packaging tape’ works better than the usual roll-type transparent tape)

The low cost of these materials and their reusability makes this an ideal class-wide experience.  Further student explorations are readily accomplished by using a variety of magnet types, numbers, locations, polarities, and shapes.  Applicable magnet types (also available from Educational Innovations) are

Ceramic Bar Magnets (0.875” x 1.875”)

Ceramic Ring Magnets (1.25” O.D.)

Neodymium Ring Magnet (0.75” O.D.)

Neodymium Large disk (1” O.D.)

Similar demonstrations can utilize larger magnets and larger bottles.  This one uses a 2-1/2 inch diameter bottle and two large (2” O.D.) ceramic ‘donut’ magnets removed from the magnetron in a discarded microwave oven.

And this one illustrates the magnetic field created by a 2” O.D. ceramic ‘donut’ magnet placed under a 2-1/2” diameter bottle.

CAUTION: Rare earth magnets are very strong and very brittle.  They will attract each other quite unexpectedly.  There always exists the possibility of fractures and flying pieces. Everyone MUST wear safety glasses/goggles when working with these magnets!

Marty Sagendorf is the author of 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.

## Iron Filings Exploration

June 11, 2010

by:  Michelle Bertke

Simple iron filings can be used for a variety of interesting experiments and demonstrations.  Magnetism is a mysterious concept that can be difficult for students to grasp.  Magnetic fields are the forces surrounding a magnet that are identified by how they interact with adjacent magnets and other metal objects.  While magnetic fields are ‘invisible’ they can be observed by sprinkling iron filings on a white paper with magnets beneath.

By lightly coating the surface of the paper, the magnetic field will appear as filings align themselves with the field.  Different magnets, depending on their strength and shape will create varying patterns in the iron filings.  A bar magnet with a distinct north and south will show characteristic lines of a magnetic field.  Circular magnets may show multiple lines indicating multiple magnet fields.  The stronger neodymium magnets will cause the iron filings to pile up in spikes due to the increased strength. This demonstration can lead to a discussion about magnetic fields: What they are, Where they can be found, and How they are used in the world around us.

A simple magnetic fluid can be prepared by mixing iron filings with vegetable oil.  This fluid will flow when free from a magnetic field and stop solid when next to a magnet.  The mixture can be put in a glass or plastic vile so students can observe how the fluid flows.  When the fluid is held over the magnet, it will pile up (as long as it is in the range of the magnetic field).  When the magnet is removed, the tower will collapse into a puddle.  Students can then experiment with magnets of varying strengths to observe how the strength of a magnet will affect the height of the tower that is able to be formed.

Iron filings can also be mixed with sand to illustrate how different substances interact with magnets.  A pouch can be made out of freezer bags.  (You will want to hot glue the openings to prevent spills, as seen in the picture.)  When filled with a mixture of sand and iron, the bags can be made to appear homogeneous.  You can ask your students what they think is in the bag.  (Some perceptive students may come up with the correct answer depending on prior knowledge and the previous activities.)  You can also ask if they think they would ever be able to separate the two substances.  When you drag a magnet along the surface of the bag, the iron filings come to the surface, separating from the sand.  This simple illustration can lead to discussion of what is magnetic and why.

This is also a great activity to relate the idea of magnetism to a household toy that they should all be familiar with: the etch-a-sketch.  This toy relies on a similar set up to make designs and, like our sand pouches, the designs disappear when the toy is shaken.  A discussion of other applications of magnetism in the home will likely follow.

Michelle is a graduate student at the University of Notre Dame.  She and another graduate student, Melanie Bunda, run a program called Science and Stories.  This program focuses on children from ages 6 to 10 and allows the participants to explore science though books.  They use a number of Super! Wow! Neat! science supplies from Educational Innovations.

## Our Magnetic Field

June 1, 2010

by:  Martin Sagendorf

We recognize heat & cold, dry & damp, light & dark, and sound & silence.  However… I find it absolutely fascinating to consider that we also live within something that we can’t see, hear, touch, or taste.

We all Know:

Our planet has a giant magnet near its core and that its field extends over the whole of the Earth’s surface.  But, do we ever really think about this field that passes through soil, rocks, buildings… and us? Granted, relatively speaking this ‘field’ isn’t particularly strong.  In fact, it’s a rather weak field when compared to those of a horseshoe magnet or, particularly, a modern Rare Earth magnet.

A Great Demo:

Uses a few very strong Rare Earth magnets to illustrate that this field really is everywhereeven in the classroom.  What we want to make is a really graphic and dynamic demonstration.

It’s Easy to do:

Just hang a magnet from the ceiling – Any bar or ‘donut’ magnet will align itself to the Earth’s magnetic field.  Here’s a very effective construction:

Materials:

• A new pencil with eraser (7-1/2” long)
• 6 rare earth (Neodymium) ring magnets (E.I. Neodymium Ring Magnets #M-185)
• 5 feet of light-weight string or heavy thread (or very light fishing line)
• A ‘flag’ indicating N (cardstock: 3/4” x 2-1/2”)
• A 24” length of 3/4” or 1” wide masking tape
• A few inches of clear tape or Glue (Duco®)
• A very small ball bearing ‘fishing swivel’

Construction:

• Sharpen the pencil
• At 3-1/4” from the top of the eraser, tie one end of the cord around the pencil (look on the Internet to see how to tie an ‘Improved Clinch Knot’ – use two turns – this knot really works quite well)
• Using a single Ring Magnet as a measure, wrap masking tape around the pencil on both sides of where the string is tied to the pencil – wrap-on sufficient lengths to make a snug fit for the magnet (this will be about 12” per side)
• Make up two magnet stacks with three magnets in each
• Use a magnetic compass to determine the ‘polarity’ of the stacks – the stack ends that attract the south-pointing end of the needle are the ‘north ends’ of the magnets – you’ll want these ends to be towards the sharpened end of the pencil
• Slip the stacks of magnets over the ends of the pencil – the stacks will be aligned so they are attractive – carefully move the stacks together (on) each side of the cord
• Hang the assembly from an overhead support
• Place the N flag over the sharpened end of the pencil – centered about 1-1/2” from the pencil point
• The pencil should hang nearly horizontally
• To adjust any deviation from horizontal, add some masking tape on the appropriate side of the pencil
• Once level, use clear tape or glue to fasten the flag
• Splice the fishing swivel into the cord – about 12” above the pencil – use knots as above

In Use:

Suspend the unit from the classroom ceiling such that it is just accessible for ‘spinning’ by students entering the classroom.  This will become an everyday occurrence.

This Simple Device Illustrates:

• That the Earth’s magnetic field is everywhere
• A force we can’t see or feel (directly)
• ‘Force-at-a-Distance’
• That the very small magnetic field (force) from a nearby hand-held magnet is sufficient to cause a disturbance in the ‘local’ magnetic field (even if a magnet is totally grasped within one’s hand – the magnetic field simply goes right through one’s hand)

Notes:

• These little magnets are very strong – be very careful when handling them
• When separating the magnets, slide them apart one-by-one
• When placing magnets together – do so with caution – they will very suddenly attract each other
• These magnets will fracture if subjected to an impact force – wear safety glasses
• Keep the magnets well away from credit cards and other magnetic storage devices
• ‘Spinning’ may result in ‘wind-up’ (a residual twist) in the cord – especially so when using a ‘stiffer’ cord (e.g. light-weight fishing line) – the pencil may ‘come short’ of pointing at North.  The fishing swivel (the smallest one you can find) will minimize this.  But, even with the swivel, there will be times that it cannot completely compensate for the wind-up – if this happens, simply lift the pencil very slightly to release the twist in the cord.  As an aside, fishing swivels usually come several to a package – choose the one with the smoothest action and place a drop of very light oil inside it.

Marty Sagendorf is the author of 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.