Monthly Archives - October 2005

Haunted Laboratory: Halloween Physics Part II

Since publishing the last Halloween edition of CoolStuff, we have received many positive comments from teachers who have created their own haunted laboratories. We have learned that teachers not only share their displays with their own ghosts and goblins but often open up their labs to the entire school or community. Therefore, we’ve decided it’s time to revisit the Haunted Laboratory in search of even more science tricks and treats.

This edition of CoolStuff features some new exhibits designed to put a spooky spin on science. The displays, selected with ease of construction in mind, use materials, and apparatus found in most science storerooms. Specialty items, such as a green laser pointer, may be readily obtained from Arbor Scientific. To make the most of your Haunted Laboratory experience, we’re offering the following suggestions from physicist and Haunted Laboratory pioneer Thomas Zepf.

  • The lab should be as dark as possible. Quite often the exhibits provide sufficient ambient lighting. However, safety is always the first concern. If necessary, use additional lighting to ensure that students are able to safely navigate the room.
  • Many pieces of standard laboratory apparatus can be modified for use in a haunted lab. Just let your imagination run wild!
  • To set the mood, decorate the room with a variety of Halloween items. Artificial spider webs, plastic bats, pumpkins, and masks are always good.
  • The overall experience is enhanced by playing Halloween music or recordings of scary sounds. Such recordings are inexpensive and readily available. You may find that your library has a wealth of suitable recordings.
  • Consider using students as facilitators. Enthusiastic and knowledgeable student helpers make the experience more enjoyable and meaningful for visitors. As is always the case, the best way to learn something is to teach it. In addition to serving as docents, students will derive a great deal by assisting in the setup of the laboratory.
  • Consider inviting students from other schools and members of the community to your haunted lab. We are certain you will find the experience gratifying.

(Note: To read Professor Zepf’s account of his experiences with haunted laboratories, see the October 2004 edition of The Physics Teacher magazine.)

Haunted Lab Exhibits

We have all seen a reflection of ourselves in a kitchen or bedroom window at night. Because we are in a room that is well illuminated and the outside is dark, light reflected by the window predominates over the light coming through the window from outdoors. We think of the glass as an ordinary mirror, often forgetting that the people on the outside can see us very clearly. This is essentially the “one-way mirror” effect used in situations where an observer wishes to remain hidden. In police stations and department stores, partially silvered panes of glass behave as mirrors to those on one side. To those in a dark room on the other side, the glass functions as a window.

everyone

The device shown above demonstrates that a transparent material may be an effective reflector as well as transmitter of light. It also illustrates that the object and the image produced by a plane mirror are equidistant from the mirror’s surface. These two phenomena make the morphing of two faces possible by simply adjusting the intensity of the light falling on two individuals sitting on opposite sides of the glass. The results of this simple exercise can be very freaky, to say the least! Things can become even spookier if one of the participants wears a Halloween mask.

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Image courtesy of Pati Sievert at Northern Illinois University

The apparatus consists of a sheet of Plexiglas and two floodlights controlled by dimmer switches. Users sit on opposite sides of the Plexiglas and adjust each light’s intensity until the image of one person’s face merges with the image of their partner’s face. It should be noted that only one participant at a time is able to observe the effect.

The photos above represent two possible setups: a more polished version of the device (Top image) and a very simple setup (Bottom image). In the simpler device, the glass from an old ripple tank serves as the reflecting surface. Two dimmers (Variacs also work well) are used to control the brightness of two standard light bulbs or two flood lamps. An eerie effect may be achieved by using different colored bulbs (e.g. orange and blue) in each of the sockets.
Instructions:

  1. Lights on apparatus may have to be adjusted so they shine on the students who will be sitting on each side.
  2. Have two students sit, one on each side of apparatus, approximately the same distance away from the apparatus.
  3. Students need to line up their eyes and nose as best as they can.
  4. Have students adjust the lights so that one is relatively bright while the other is dim. Have observers view the results from the bright side. Remind the student sitting on the dim side that they will not observe the effect.
  5. Have students reverse the lighting conditions so the student initially on the dim side will have an opportunity to see the unusual effect.

Monsters of the Deep in a Drop of Pond Water

A drop of pond water at the end of a syringe or eyedropper can be treated as a small spherical lens. The light beam that falls on the drop refracts as it passes through the water-air interfaces at both sides of the droplet. The shadows of the small creatures contained in the suspended drop of pond water are magnified up to 1000 times by the liquid lens.


The top image shows the setup for the Monsters of the Deep using a ring stand to hold and adjust the drip rate of the eyedropper.


The bottom image shows the darkroom results of the various creatures we found in our “Swamp Water”.

Image courtesy of the 2006 Arbor Scientific Staff Science Olympics. Our drop of pond water was full of creatures. It was like a Monster convention!  Because of extreme lighting conditions, it was difficult to do it justice.

This activity was inspired by an article in The Physics Teacher magazine by Gorazd Planinsic.

Water-drop projector Physics Teacher 39, 76 (2001)

Watch the laser light on the screen. You should see the magnified shadow images of microscopic organisms floating and moving within the projected light. Small single-cell animals like paramecium appear as dark spots surrounded with interference fringe contours. Larger animals such as mosquito larvae, Cyclops, or water fleas appear like real monsters on the screen.

Pepper’s Ghost

The one-way mirror (see “Freaky Faces”) has long been used in the performing arts, magic acts, and amusement parks. It was exploited for theatrical purposes in the mid-nineteenth century when J.H. Pepper produced what appeared to be a hovering apparition on a London stage. By angling a large glass plate between the stage and the audience, Pepper produced an image of an actor who seemed to hover over the stage (see figure below). To create the illusion, a well-illuminated actor was located in front of and below the stage, out of the audience’s view. A light source of variable intensity was employed to make “Pepper’s Ghost” come and go at will. A darkened theater insured that unwanted reflections would not reveal the presence of the glass. Similar techniques are currently used in amusement parks and museums to startle and amaze unsuspecting visitors.

You can create a simple version of the Pepper’s Ghost illusion with a sheet of glass or Plexiglas, a candle, a drinking glass and a cardboard box. First, remove the flaps from the mouth of the box. Spray the inside of the box with black paint or line it with black construction paper. Place the sheet of glass or plastic over the mouth of the box. Ideally, the sheet of Plexiglas should be the same size as the opening; however, this is not necessary. Place the box on its side with the mouth of the box facing you. Fill the glass with water and place it inside the box. Now cover the opening with the Plexiglas sheet. You may wish to tape it in position. Finally, place a lighted candle in front of the box so that the candle is in front of the drinking glass and both objects are equidistant from the Plexiglas. Now turn off the room lights. When you light the candle, the flame will appear to be burning in the water! The photos below are physicist Dave Wall’s Pepper’s Ghost device.

A setup resembling the original Pepper’s Ghost apparatus may be constructed from a large sheet of glass or Plexiglas, a light source, and a person in costume or a scary mannequin. The reflecting sheet should be slightly taller than the observer. A smaller sheet may be used by raising it with supports.

A glass of water is placed at the exact location of the reflected image.

Here the actual candle is shielded from the viewer by a partial cylinder.

A costumed person or mannequin stands in front of the Plexiglas. When the person or mannequin is illuminated, a ghostly image will appear behind the clear reflecting surface. It’s fun to watch a friend go behind the Plexiglas and put their arm around the image or pass their hand through the body of the image.

The Reverse Mask

Key Concept:
This exhibit consists of a reverse mask. That is a mask that is intentionally set up to be viewed from the wrong side. The display demonstrates that our eye-brain system is conditioned to interpret all faces as convex even when they are not.

Teacher Instructions:
The centerpiece of this display is a white translucent mask. In the photo, a mask of Einstein is shown (see below for details), but any inexpensive mask will work.  Simply place a standard light bulb behind the reverse mask, stand approximately 10 feet away and view the mask with one eye closed. Presto! The concave face will appear convex! Once the illusion is established, open both eyes. If you are like most people, you will still see a convex face. Now move from side to side. The face will follow you wherever you go!

When we look at a reverse mask, our eye-brain system perceives a normal face for two reasons: shadowing and expectation. We are accustomed to seeing subtle shadowing when human faces are illuminated from above. These shadows tell us that the face is in relief. Similar shadowing is produced when light passes through the translucent mask. Perhaps an even more important factor in establishing a sense of convexity is expectation. Since we virtually never encounter a concave face, our previous knowledge tends to override reality. That is, we tend to see what we believe rather than believe what we see.

As we move past the mask, we see more of one side of the mask than the other. Based on experience, we interpret this change in perspective as being caused by the rotation of the face rather than a change in viewing angle.

If we get too close to the mask, we receive visual information that destroys the illusion of convexity. For example, reflections from the plastic surface often reveal the true curvature of the mask.


Image courtesy of Pati Sievert at Northern Illinois University

Einstein Alive

In Stock SKU: P2-6000
$20.00

Student Instructions:
Stand a few feet away from the mask. With one eye closed, look at the mask. Does the mask appear concave or convex? Now open both eyes. Does the mask continue to look convex? Finally, with both eyes open, move from side to side. Can you escape the gaze of the mask?

Ghostly Messages

Using a little Tide or Cheer and a black light, you can make messages and scary images appear seemingly out of nowhere. Many liquid detergents contain fluorescent dyes. These dyes serve as whitening agents that are intended to make yellowed clothing look white and brighter. When illuminated with ultraviolet light, these liquids fluoresce, giving off a cool blue light. By mixing roughly equal parts of detergent and water, you can produce a “paint” that is invisible in white light but fluoresces dramatically under black (ultraviolet) light. You may write a message or draw with your finger tip or a brush on a tabletop, wall, or sheet of paper. Once it has dried, your painting will be virtually invisible in normal light but readily visible in ultraviolet light.



Image courtesy of Pati Sievert at Northern Illinois University.

The Oozing Flesh Display

This exhibit illustrates an effect often called the “Waterfall” or “motion aftereffect” illusion. If you stare at a waterfall, cells in the eye that sense downward motion becomes fatigued. If you shift your eyes to the side of the waterfall, the nearby rocks appear to float upwards because the cells that sense upward motion are not tired and send a stronger signal to your brain. This causes your brain to conclude that the rocks are moving upwards. The same effect can be observed if you stare at a road while in a moving car and then divert your gaze to a stationary object.

Similarly, eye cells that detect rotation in one direction become fatigued and are overpowered by cells that detect rotation in the opposite direction causing the sensation of reverse movement.

squirm2

DotsImage

To duplicate this effect, print out the dotted disk and attach it to a slow-moving turntable. An old record player set at 33/13 or 16/2/3 works well. You can get your skin to seem to ooze by following these steps: Stare at the center of the spinning disk for 30 seconds.
After 30 seconds of staring, look at the palm of your hand, face or arm.
Does your flesh seem to be oozing? Does it appear to turn in the same direction as the disk or in the opposite direction?

Try looking at objects in the room after staring at the disk for 30 seconds.

If you don’t have a turntable, mount the disk on a piece of circular cardboard. Then attach the center of the disk to a pencil’s eraser with a thumbtack. Spinning the disk at a fairly constant rate by hand is guaranteed to get your skin crawling!

See more Haunted Physics Lab Exhibits

We started discussing the idea of the Haunted Physics Lab in CoolStuff #11, released October 2003. You can see other haunted exhibits from that issue and much more by visiting the CoolStuff Archives. Every issue is added to the Archives and is searchable by topic, title and volume number.

Did you read Haunted Laboratory: Halloween Physics part 1? if not check it out.

Haunted Laboratory: Halloween Physics part 1

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Exploring Matter: Chemistry Demonstrations


In this issue of CoolStuff, we’ll once again welcome guest author Patty Carlson. At New Trier High School, Patty is known for her ability to make chemistry come alive. Her flair for great demonstrations and labs certainly comes through in the upcoming collection of activities illustrating properties of matter. I know you’ll enjoy sharing these marvels with your students! I have known and worked with Patty Carlson for over a decade and feel privileged to teach and grow with her. Patty is an energetic, creative, and caring professional who has earned the respect of her students and the admiration of her colleagues. She relates well to students, knows her subject inside and out, and is enthusiastic about sharing her knowledge with others. Patty is intrigued by the simplest things, which, I believe, explains her success. She seems more fascinated with the natural world around her each day and she shares this growing sense of wonder with her students.

Exploring Matter Activities

Chemistry is all about studying matter and how it changes. Fortunately many characteristics of matter are macroscopic, that is, we can directly observe them without the aid of any lens other than those in our own eyes. We can watch as matter is mixed or reacted and ultimately may be able to infer something about its deeper, more abstract structure (electron configurations that determine bonding, or the pairing/ unpairing of electrons that result in the magnetic properties of certain elements, the molecular shape of a molecule that influences its polarity, or the “packing” of atoms that determines the density of a substance.)

In the following activities students are encouraged to poke, prod, pour and play (wow…..that’s a lot of alliteration…) with matter and watch as it responds. I’ve found over the years that using familiar, household items as much as possible reduces the intimidation factor that some students feel in physical science classes, especially in the beginning of the year when many of the concepts explored below are introduced. The Reddi-Whip will go fast as will any extra soda you might have leftover to wash it down. Make sure you have lots of Styrofoam cups too because even my high school students want to see that acetone/cup demo over and over and over and over…

Patty Carlson ~ New Trier High School, IL.

I. Like Dissolves Like

Ever have a nasty stain on your shirt that won’t come out in the wash, no matter how many times you try, and yet that same stained shirt comes back from the dry cleaner looking like new? If you have, you’ve experienced the chemical phenomenon of “like dissolves like”. That is, substances tend to dissolve in things that are similar to them. By ‘similar’ in this case we mean in terms of their polarity. Some stains dissolve better in a polar substance like water and some stains require a more non-polar substance to dissolve them away.

Let’s consider two solvents that are pretty different in their polarities in order to explore this topic. Water, which we said is a polar solvent, dissolves almost anything that is polar, such as salt and many other ionic compounds. Water can’t dissolve everything, though. Try removing fingernail polish with water and you’ll see what I mean. Acetone, a solvent with some non-polar properties, is commonly used to do that job. Acetone is an effective solvent for all sorts of non-polar substances.

Demo:

Place two large glass beakers side-by-side. Pour water into the first beaker until it’s about half full. Place a Styrofoam cup in the water beaker. Nothing will happen. Styrofoam is non-polar, water is polar and, since “like dissolves like”, they will not dissolve in each other.

The goo you retrieve from the beaker is actually polystyrene plastic (#6 in recycling code) and is the same plastic used to make plastic table ware, etc. You can shape it any way you wish while it is wet and it will harden over time as all the acetone completely evaporates away. In order to completelydissolve the plastic, you’d need a stronger and more non-polar solvent.

Now pour some acetone into the other beaker and place another Styrofoam cup into that beaker. You’ll see the cup slowly break down until it is just a glob of goo. Acetone can get in between the components of the polymer of plastic and allow the air in the cup to escape (don’t worry, they don’t use CFC’s in Styrofoam anymore so there is no harm to the environment when doing this demo).
Place starch packing peanuts (the environmentally friendly packing option commonly used today) in a beaker of acetone. Since the starch packing peanuts are polar, they will not dissolve in acetone. Put the starch packing peanuts in a beaker of water, mix around a bit and you’ll see they dissolve readily

Starch peanuts in acetone

Old-fashioned Styrofoam packing peanuts are fun to play with too. You’ll need a large beaker filled about half full with acetone. Have someone ready with a large wooden spoon and start loading the Styrofoam packing peanuts into the beaker as your helper stirs like crazy. You’ll be amazed at how many peanuts will fit into the beaker.
II.  Density: 

An interesting and often surprising property of a substance is its density, or the ratio of a certain mass of that substance to its volume. As long as you keep the temperature the same, the density of a particular substance never changes. You may have felt how heavy a chunk of lead is compared to a chunk of aluminum of the same size or perhaps you’ve held a jar of metal mercury and been amazed by how heavy even a small amount of this element is. These are differences in density. Since chunks of lead and jars of mercury are a little hard to come by, let’s explore this with some pretty ordinary stuff: Coke and Diet Coke.

Demo:
Get a large, glass beaker (or aquarium) filled with water, a can of Coke and a can of Diet Coke. Place both cans in the water. The Coke will sink; the Diet Coke will float. Ask students to hypothesize about why this is so. (Caption: The difference between the two densities is real, but subtle. Make sure to do this in a large volume container (1000-2000 ml) in order to make the difference as obvious as possible.  The density if Coke is slightly above 1.0 g/ ml and the density of Diet Coke is just about 1.0 g/ ml. The density of water (at room temp) is 1.0 g/ml. We assume the aluminum cans are identical in density.)
Activity/ Lab:
Challenge your students to design an experiment that will allow them to determine exactly what the densities of the two sodas are. This can be done easily using small graduated cylinders (10 ml) and an electronic balance. For example, they can pour 2 ml of coke into the graduated cylinder, place the cylinder on a balance and record the mass. (Of course, they should correct for the mass of the graduated cylinder.) This would be their first “data point”. They can repeat this technique with 4 ml, 6 ml and 8 ml of the Coke and corresponding masses for those volumes. This entire process is repeated with Diet Coke. Make sure students don’t get them mixed up. They may taste different, but they look identical in the lab.Once they have gathered their data, can find the density by one of two methods: graphing the data and finding the slope of the mass vs. volume line (most accurate), or simply finding the average density from the data points. When graphing, students should include 0,0 as a data point, since zero volume of soda has a mass of zero.The students will probably guess that the only real difference between these sodas is the sugar content. Coke contains approximately 39 grams of sugars (high fructose corn syrup and/or sucrose, which is regular old sugar) . Diet Coke contains Nutrasweet (aspartame) and since Nutrasweet is SO much sweeter than sugar, only about 100 milligrams per can are required to get it to match Coke’s level of sweetness. That’s a pretty big difference and the reason for the difference in densities of the two sodas.If you want to make it more interesting, try the new low-carb Coke, C2, and see where its density falls with respect to the other two. It contains a combination of artificial sweeteners (aspartame, acesulfame potassium, and sucralose, which is Splenda) in addition to high fructose corn syrup and/or sugar. You can also try different brands. Tab contains saccharin and Diet Rite uses a combination of artificial sweeteners, giving them a slightly different density.
III. Density Columns:
Here’s a Demo and/or Activity that uses the concept of “like dissolves like” and density! You’ll need: Dark Karo syrup, Water (with food coloring too help students identify which layer it is in the column), Vegetable oil, Rubbing alcohol (isopropyl alcohol), and Large glass cylinder (or any long tube will do. It doesn’t have to be graduated). To do this as a demo, take the glass cylinder and pour in the dark Karo syrup (the most dense in this list). Then carefully pour in the colored water. You’ll note that they mix a little bit (there will be a “blur” between the two layers), but they are still distinctly layered. (The sugary syrup has some polar properties and the water will dissolve it at the point of contact.) Then pour in the vegetable oil. Because oil and water don’t mix (oil is non-polar, water is polar) they will also form distinct layers. For the last layer, add the rubbing alcohol. This can get messy and the column will need time to settle itself down. The alcohol will dissolve in water (alcohol has a polar region), but the oil will form a barrier between the water and alcohol. When you pour the alcohol into the column, it will come into contact with the oil and go from clear to murky. Again, there will be a blurring of the “line” between the two layers due to partial solubility (rubbing alcohol has non-polar parts too and oil is non-polar so a little mixing will occur).
To do this as a lab activity, give students smaller columns and the same 4 liquids. Let them pour the liquids in any order they wish. Based on their observations, they should be able to figure out which liquids are more dense than which others. Finally, they will be able to rank the liquids according to their relative densities. Rubbing alcohol 0.87 g/ml Vegetable Oil 0.91 g/ml Water 1.00 g/ml Dark Karo Syrup 1.37 g/ml To add a little complexity to this activity, ask the students to infer the approximate densities of the following solids: Ball bearing, Plastic bead, Cork, Rubber stopperThey can do this by dropping the objects, one-by-one, into the column and see if they float or sink in a particular layer. If they know the numerical value for the densities of each of the 4 liquids, they can approximate a value for the density of each of the solids.  Students should observe the following sequence, in order from least to most dense: Cork – Rubbing Alcohol – Vegetable Oil – Plastic Bead – Water – Rubber Stopper – Karo Syrup – Ball Bearing
IV.  Classification of Matter:
Matter is anything that has mass and takes up space (has volume). We can separate the matter that we know about into two huge categories; mixtures and pure substances. Well, what are mixtures? Mixtures are physical combinations of at least two pure substances. Most of us are much more familiar with mixtures than pure substances and they are indeed much more common in our everyday experiences. For more on mixtures, check this out:
http://www.factmonster.com/ce6/sci/A0833482.html.
Mixtures can be further categorized into homogeneous and heterogeneous mixtures. Homogeneous mixtures are mixtures with the same composition throughout. Let’s say you stir some powdered Kool-aid mix into a pitcher of water. Once the powder is dissolved, doesn’t that Kool-aid look and taste the same from the first sip to the last?  Compare that to some orange juice with pulp in it. Let’s say your brother never shakes up the carton when he pours himself a glass of juice. By the time you get it, there is a huge blob of pulp at the bottom of the carton. Now your glass is a combination of juice and big globs of pulp. That, my friend, is a heterogeneous mixture and a gross one at that. Heterogeneous mixtures are not uniform in composition at all. Now, what are pure substances? These are either individual elements right from the Periodic Table or compounds (chemical combinations of those elements). The element Iron, for example, is a pure substance. Let’s say we let that iron sit around outside for while and we notice it starts to rust. It has undergone a chemical reaction and combined with oxygen in the atmosphere to create iron oxide, which is a compound, and, by itself, also a pure substance. These elements aren’t “mixed’ together like the mixtures we talked about before, they are BONDED together in a chemical way that won’t allow you to un-bond them very easily. Getting confused? Let’s take a look at some examples and maybe things will clear up…

Student Activity:
This is a station-based activity (or “smorgasbord” as my buddy Chris Chiaverina calls them) so you’ll need lots of lab space and a place for kids to walk around in small groups. Collect items like the following (and/or add your own!) and place them around the lab benches. Ask the students to:

1) Identify the category of matter:
a. Is it a pure substance? If so then is it an element or is it a compound?
b. Is it a mixture? If so, then is it a heterogeneous mixture or homogeneous mixture?
c. (Optional) Have the students write down the criteria they use for their categorization schemes.

Devise a separation strategy for any mixtures found. In other words, if you think you’ve spotted a mixture, how would you separate it into different components, and (if possible) all the way to the pure substances that comprise the mixture? (Remember, pure substances cannot be separated by physical means. They must be separated chemically, or, in the case of elements, by splitting atoms! That’s beyond the scope of the activity for the day.)

Suggested Items:
1. Aluminum foil: (Pure substance, element)
2. Lucky Charms: (Heterogeneous mixture.)  Separate physically. Visually identify the cereal from the sugary charms and manually sort into two piles. Separation beyond this is too difficult.
3. Orange juice with pulp: (Heterogeneous mixture.) Separate by gravity filtration of the pulp.
4. Salt water: (Homogeneous mixture.) Separate by boiling away or evaporating the water and leaving the salt crystals behind.
5. Salt, sand and water: (Heterogeneous mixture.) Separate by filtering out the sand, boiling off water and leaving salt crystals behind.6. Reddi Whip dessert topping: (Homogeneous mixture…really a colloid, but that may be too fine a point here.)  Separate gas from solid portion by heating it. Gas will bubble out since less soluble at higher temps, leaving solid portion behind. Separation beyond this is too difficult.

7. Oil and vinegar salad dressing:(Heterogeneous mixture.) Separate by difference in density.  (A separatory funnel is a good tool for this.)

8. Chocolate Silk Jif: (Homogeneous mixture.)Separation strategy: good luck J Some homogeneous mixtures are so uniform, even at the microscopic level, they seem extremely difficult to separate by conventional means.

9. Aspirin (make sure this is pure aspirin with nothing added, like buffers or anything else): (Pure Substance, compound – acetylsalicylic acid.  All aspirin is this compound. People buy different aspirin products for different reasons. Buffered aspirin helps those prone to stomach upset, etc…)
10. Juice Bar Candy Refreshee Spray Perfume:
(Homogeneous mixture.) Separate by differences in boiling point using fractional distillation. (What’s that? Check this out:http://chemistry.about.com11.Iron and Sulfur
(literally iron filings and powdered sulfur): (Heterogeneous mixture) Separate by difference in magnetic properties.

12. The Ink in a Black Sharpee Pen:
(homogeneous mixture.) Separate by chromatographic means. That is, the different pigments in the pen that make “black” can be separated based on their solubility in different solvents of different polarities.
Demo Idea:
Combine the iron and sulfur mixture from # 11 in a test tube.  Heat over a bunsen burner under the hood, you can show the students that a new substance is chemically formed. It is a pure substance and a compound, iron sulfide (FeS). It no longer has any magnetic properties at all and proves that is has been chemically changed from two elements to a single compound with completely different physical properties.

What’s the Matter?

A look at some weird solidy-liquidy type stuff:

We are all probably aware of the basic states of matter: solids, liquids and gases. When we see a solid, we expect it to act like a solid, that is, have a definite volume and a distinct shape (at a given temperature). When we see liquids we expect them to behave like liquids. They should flow easily, no matter how hard or gently we stir them around.

Are there substances that don’t behave the way we think they should? Sure! They’re called non-Newtonian substances.

Slime Receipt Things you’ll need:
Thermometer
Electronic balance
150 ml beaker
glass stirring rod
disposable cup
Hot plate
10 ml graduated cylinder
Hot mitts
De-ionized water
Polyvinyl alcohol (PVA) the powder form
Saturated Borax solution (add enough borax to water so that it turns cloudy. You can put it on a magnetic stirrer to keep the particles suspended)

  1. Mass out 2.00 grams of the PVA. Set aside.
  2. Pour 50 ml of deionized water into the beaker. Insert the thermometer into the beaker and place the beaker on the hot plate. Heat gradually to about 90 degrees. Do not let it boil rapidly or you will lose too much water and your slime will be stiff.
  3. SLOWLY sprinkle in the 2.00 grams of PVA and stir constantly with your glass stirring rod. You will know if you are going too fast if there is a glob of material at the bottom of your stirring rod.
  4. After you have completely stirred in all 2.00 grams of PVA, turn off the hot plate and keep your beaker on the hot plate so it doesn’t cool off. 
  5. Get 5.0 ml of Borax solution.
  6. Take your disposable cup and simultaneously pour the PVA solution from the beaker (use hot Mitts!!) and the Borax solution together in the disposable cup (NOT the beaker) and stir.
  7. A gel-like substance (SLIME) should form immediately. If it doesn’t, keep stirring. Sometimes when the solutions get too hot it takes a while to get the slime to form.
  8. Add food coloring to make really gross slime.
Now, why is this a Non-Newtonion Substance? Because it behaves differently depending on how gently or strongly you stir or pull it. If you pull it slowly, it will stretch and ooze sort of like a liquid. If you pull it apart quickly, it will stiffen up and break cleanly in two as if it were a solid. You’ve heard of quicksand, right? It is also a non-Newtonian substance. Maybe you’ve seen movies where someone is trapped in quicksand and cant’ get out. The harder they thrash around to get out, the worse it is for them. Can you explain why? Think about your slime. The harder you force it, the more rigid it becomes, so the person gets even more stuck in the quicksand. To save themselves, they should move very slowly to get out so they quicksand would behave more like a liquid and not resist the person as much. Ketchup is another non-Newtonian substance, but it behaves in the opposite way. Glass bottles of ketchup used to be common, but they are probably only seen now in restaurants. Ever try to get the ketchup out of this kind of container? It flows better with more agitation! You may have had to shake the bottle pretty violently several times before it actually starts to flow out of the bottle.
Easy Slime Alternative Lab
1 cup of cornstarch
1/2 cup of water
food coloring
1. Put cornstarch in bowl
2. Slowly and with stirring (hands are fine) add the water.
3. Add food coloring as desired
4. Test your cornstarch slime by hitting hard, then softly. Try to stir it quickly, then very slowly and gently. Note observations and have fun!
VI.  Desalinization by Distillation
This re-printed lab from Physical Science: Concepts in Action is courtesy of Pearson Prentice Hall. It instructs students in the concepts involved in the distillation process. They use both an active process (boiling) to distill salt water, and a passive process (solar evaporation). Click here to print a copy of the teacher’s version of this lab. Click here for more information on Prentice Hall’s Physical Science: Concepts in Action textbook and resources.
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