‘Tis the season for holiday specials! Whether you like Charlie Brown, cute animals, or wacky elves, there is a Christmas show for you. Modern television and movies are a relatively recent innovation, but the process of producing a more and more realistic moving image has been underway for much longer. The thaumatrope, zoetrope, praxinoscope, phenakistoscope, and flip books are examples of the evolving technology for producing moving images. To see examples of these in action, visit one of the links below:
It is easy to build your own version of a thaumatrope, zoetrope, or flip book. Simply use your favorite search engine and select the set of directions that you like the best. Here are a few things I learned while building my own zoetrope:
- You should have at least 12, but ideally 24, equally spaced vertical slits around the circumference of your zoetrope.
- The slits should be about 1/8th inch wide, but no wider.
- The number of slits and number of images in your animation should be equal.
- Bold, high contrast images work best. A bold, dark line separating the images may also help.
- A faster rate of spin provides a smoother animation. One rotation per second is a good goal.
In the past, it was believed that we perceive moving images because of “persistence of vision.” This is the same reason you see an afterimage if you look at a bright light or stare at something. However, science now attributes our ability to see moving images to something called the beta effect. Visit The Brain from Top to Bottom to find out more about our perception of moving images and other interesting information about our sense of vision.
Happy Thanksgiving! The foods on your plate can be used to illustrate some very interesting math concepts. Enjoy!
In the following set of short, lighthearted YouTube videos, Vi Hart shows you geometry with potatoes, vectors with green beans, binary trees with turducken, and Borromean rings with onions!
The kernels of corn on the cob are generally irregular hexagons. Hexagons maximize the area to the perimeter and they are also really great at tessellation. Examples of hexagons around you are: honeycombs, wasp nests, snowflakes, Allen wrenches, pencils, some animal scales, and some carbon molecules. The tendency toward hexagons for certain circumstances is one of many instances of mathematical patterns in nature.
Please refer to the previous post to find out more about leavening, because Thanksgiving is better with fluffy rolls!
When baking soda, or baking powder that contains baking soda, is added to the recipe there is an immediate chemical reaction. The baking soda is a base, and when it is mixed with an acid, carbon dioxide is released. Recipes that use baking soda as a leavener will direct you to mix the dry and wet ingredients separately then combine them at the end. Also, these recipes will direct you not to over mix. Both of these directions are intended to capture as much of the carbon dioxide from the chemical reaction as possible and not release it before the bread is cooked. To watch this process in action, stir some baking powder into warm water. Also, cook some of your favorite pancakes, biscuits, or banana bread!
Yeast, on the other hand, is a living organism. It is a single-celled fungi that eats sugars and starches and produces carbon dioxide as a by-product. This process is much slower than the reaction of baking soda. It can take two to three hours for yeast bread to be ready to bake. The yeast continues to produce carbon dioxide until the baking process becomes hot enough to kill it. To try it, you can mix one tablespoon baker’s yeast with two tablespoons warm water, allow to stand for five minutes, then add two tablespoons sugar. Set this mixture aside and watch it for two to three hours. Doughnuts, rolls, and sandwich bread are all examples of breads that use yeast for leavening.
As a bonus, in the Elephant Toothpaste experiment, yeast acts as a catalyst to release oxygen from hydrogen peroxide. Mix one table spoon baker’s yeast with two tablespoons warm water, let stand, then add a half cup of hydrogen peroxide. Some dish soap and food coloring is optional. This reaction will last about 20 minutes.
The last post was about polymers, sometimes called slime. Corn starch was one example. When mixed with water, corn starch forms an interesting, slimy substance that has non-Newtonian properties. It is often called oobleck.
The molecules in a Newtonian fluid flow past each other easily, but they maintain the same density and viscosity (flow rate) regardless of stress as long as the temperature is constant. On the other hand, a non-Newtonian fluid reacts quite differently to stress. For some non-Newtonian fluids, the viscosity goes up under stress. These are called shear thickening. For others, the viscosity goes down under stress. These are called shear thinning.
Oobleck is an example of a shear thickening non-Newtonian fluid. Press it or hit it, and it acts like a solid. It may even form cracks. Handle it gently and it flows like thin pancake batter.
DO try this at home! Rheology is the study of the flow of matter, particularly liquids, and oobleck is a great place to start:
Oobleck with kids, what to do and not to do: http://www.learnwithplayathome.com/2013/08/cornflour-slime-how-to-make-and-what.html
How to make oobleck dance:
(I didn’t have a suitable speaker and was able to use my rotary sander under the metal pan.)
Walking on oobleck:
For an overview of non-Newtonian fluids with references to sci-fi:
Here is some information about some possible future uses of rheology:
Use your favorite search engine to find other examples of non-Newtonian fluids. What other ways could they be used?
Halloween is this week, and what would it be without a little slime? Slime is an informal name for polymer. Polymers are very long molecules with repeating segments. These long chains can be connected to each other with chemical bonds. To find out more about polymers, visit this amazing, kid-friendly site: http://www.pslc.ws/macrog/kidsmac/wiap.htm
Slime is very easy to make, has few ingredients that you may already have at home, and can even be made from edible ingredients. Try these links or search for your own recipes:
Remember, you can add food coloring, glitter, glow in the dark paint, small plastic objects, shaving cream, and more to your slime for different effects! If you store your slime in an airtight container, it should last several days.
My favorite slime recipe used glue and liquid starch. Which was your favorite?
Daniel Bernoulli discovered in the 1700s that when a fluid is moving quickly its pressure is lower. Examples of this include:
-the curved shape of a wing (also Frisbees and boomerangs) means the air on top is moving faster, creating relatively low pressure, and the air below the wing pushes it up toward the low pressure creating lift;
-when a large vehicle passes you, the moving air behind it creates an area of low pressure, which the air behind you pushes you toward; and
-the falling water from your shower causes the air to move, this creates a low pressure area and the air outside your shower pushes the shower curtain toward you in an attempt to equalize the pressure.
In addition to these examples, there are many experiments you can do to explore the Bernoulli effect further. Each of the links below have multiple experiments to try:
And, now that you can spell “Bernoulli” use your favorite search engine to find much more, including some very interesting videos!
The previous post discussed pressure using nails and knives. Another example is atmospheric pressure (fluid). We live at the bottom of a deep layer, sometimes referred to as an ocean, of air. Gravity pulls down on that air with enough force to push on each square inch of our bodies with 14.7 pounds of pressure at sea level! Higher elevations have less air above them and have lower pressure, lower elevations have more air above them and higher pressure.
Here are a couple of videos with more information about atmospheric pressure:
http://www.youtube.com/watch?v=xJHJsA7bYGc (from ScienceOnline)
Going into the deep ocean increases the amount of pressure immensely. Check out this article for some deep sea physics and biology, it is fascinating:
As always, use your favorite search engine to find out more!
Which works better: the dull “back” side of a knife blade or the sharp side of the blade? Obviously, the sharp side is better at cutting and this is due to a simple formula: Pressure equals Force divided by Area. The blade of a knife applies the force from your muscles through the knife to a much smaller area than the dull side of the knife. In the Imperial system we measure pressure using pounds per square inch (psi). In the metric system the unit of pressure is a Pascal.
Likewise, one nail can pop a balloon with very little force because all of the force is being applied through the point. However, much more force has to be applied to the balloon in the image above before it will pop. Click on this link to see a short video of the balloon under pressure:
Here are some links to more information about pressure:
The speed of light is 186,282 miles per second in a vacuum. That is really fast. Light can travel 7 ½ times around the Earth in one second! The speed of light is a very important number in physics because nothing can go as fast as light in a vacuum (empty space) and the speed of light in a vacuum is a constant.
However, light appears to pass through substances at different rates of speed.* As the light passes into a substance at an angle- from air to water, for example- the light wave will bend slightly as one side of the wave strikes the water before the other. This is called refraction.
The angle of the bend is the angle of refraction, and substances that appear to slow light the most have a high index of refraction. Eyeglasses, magnifying glasses, microscopes, telescopes, and prisms are all examples of how people use lenses to bend light.
Of course, refraction happens in nature, too. To learn more about why the sky is blue but the sunset is orange-red, try this experiment. All you will need is water, milk, a container, and a flashlight. Hint: I found that a long container worked better than a shorter one. I used a clear plastic container about the size of a shoe box.
*Really light travels the same speed no matter where it is, but some things make light bounce around a lot inside of them and travel a longer path to get out. That makes it SEEM like the light is moving slower in some substances.
For example, the dense structure of a diamond slows the apparent speed of light to less than half the speed it passes through a vacuum. This high index of refraction is why diamonds are so sparkly!
Robert Jemison van de Graaff invented an electrostatic generator in 1931. It was used to power a particle accelerator and nuclear medicine experiments and is now housed at the Museum of Science in Boston.
The van de Graaff generator generates high voltage by in the same way you do by rubbing a balloon on your hair or scuffing your feet across a carpet. It uses materials far apart on the triboelectric series to generate an electrical charge. Things on one end of the scale tend to give up electrons and things on the other end tend to accumulate electrons. In this case, the charge accumulates inside the sphere at the top and generates an electrical field. How Stuff Works has a much more detailed explanation of electrical fields and the parts of a van de Graaff generator. And, follow this link to learn about a more modern van de Graaff generator at Western Michigan University. Physics4kids has a more kid-friendly explanation of electricity.
The van de Graaff also generates tiny arcs of plasma that are similar to lightning as the charge leaps away from the sphere to a grounded or oppositely charged object. Lightning is also high voltage and due to the accumulation of a charge. And, here is a kid-friendly link to information about lightning at NOAA. This is more information about lightning with some experiments kids can do at Weather Wiz Kids.
There are a lot of demonstrations/experiments that can be done with a van de Graaff generator. This link leads to an explanation of a few. Use your favorite browser to find videos of these demonstrations and more. You can also search for instructions to build your own van de Graaff! Have fun and be safe!