Friday April 25 2014
conduction

Polarized Paper

Anonymous: 
For this week's experiment, I thought we would do a simple one, but one that always entertains people.


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How Heat Moves

Number: 
0170
Anonymous: 


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thumb: 
Length: 
4:40

Science Photo of the Day #578

Science photo 578

Why do the wires on high voltage lines have those things that look like a stack of plates?

The Smell of Money

Anonymous: 
A magic trick that can teach about observation and the senses.


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A Real Tuning Fork

Anonymous: 
If you have ever played with a tuning fork, you know that they are interesting and fun, but they can also be expensive. For this week's experiment, we will use a regular fork from your kitchen to produce a beautiful tone. For this experiment, you will need:


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The Hollow Candle

Anonymous: 
This experiment was sent in by Leilah, an 11 year old list member from Indiana. It is exactly the kind of experiment I like, because it is simple, it makes you think, and it’s interesting enough to get you to actually try it, instead of just saying, "Wow, I'll have to try that some time."


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Good Vibrations

Anonymous: 
Any time you hear a sound, it is because something is vibrating. Place your fingers against your throat and hum. You will feel your throat vibrate. We usually hear sounds from vibrations that travel through the air, but solids can be much better at carrying vibrations.


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Why Wet Things Turn Dark

Number: 
0010
Anonymous: 
Why does making something wet cause it to look darker?


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thumb: 
Length: 
1:23

The Science of Pizza

Number: 
0035
Anonymous: 
Is the cheese on a pizza really hotter than the crust?


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Length: 
2:13

Cool Water

Anonymous: 

This week's experiment comes from washing the dishes. If you look back, you will find that a fair number of my experiments have come from washing dishes, which is probably the result of the state my mind is in when my belly is stuffed with yummy food. To experiment with this, you will need:

- a sink, garden hose, stream, or other source of flowing water.

Start by turning on the water, and placing your hand into it. Unless you turned on the hot water tap, or your garden hose has been sitting in the sun, the water will probably feel cool. Now cup your hands together and let the water flow into them. Keep your hands there for a few seconds, and then move them slightly, so that the water flows over your hand instead of into your cupped palms. Do you notice a difference in the temperature?

Move your hands back and forth, from letting the water flow into your cupped hands to letting it flow across your hand instead. Why does it feel so much cooler flowing across your hand?

I noticed something very similar on a recent trip to Ginny Springs in Florida. Floating gently on giant inner tube, the water did not feel that cold, once I got over the initial shock. While I was moving at the same speed as the water, I was comfortable. When I grabbed a branch and stopped myself, the water felt much colder. Why?

You are probably thinking that the water in your hand feels warmer because your hand has warmed it. You are correct! If you put a thermometer into the water in your hand, it will probably read at the same temperature as the water flowing over your hand, but that is because you are measuring the temperature of the water in the center of the pool formed by your hands. Over by your skin, things are very different. There, heat energy is moving from your warmer skin to the cooler water. Your skin is cooled, the water is warmed, and the temperature difference between the two is decreased.

That difference in temperature plays a large role in what you feel. When we say that we "get used to" the temperature of a hot bath or a cold spring, quite a bit of the process involves decreasing the temperature difference between skin and the surrounding water. The less difference there is, the less heat or cold we tend to fell. Of course, that only works up to the point were the temperature threatens to cause damage. No matter how little the difference, boiling water is still going to feel hot.

As long as the water is not moving, that thin layer of warmer water stays next to your skin. On the other hand, if the water is flowing past you, there is a constant supply of fresh, cool water, so there is a much greater temperature difference. That is why the running water feels colder, and why the flowing spring felt colder when I was anchored.

That idea also plays a role in wet suits used for surfing, diving, and kayaking. The suit does not keep the water out. That is why it is called a wetsuit. If you can't keep the water away from your skin, the next best thing is to protect that layer of warmed water next to your skin. The wetsuit keeps it from being swept away as you swim, dramatically reducing the amount of heat that you lose. If your wetsuit fits loosely, your movements will cause that layer of warmed water to squeeze out, letting fresh, cold water flow back in. I can tell you from my experience kayaking, that is a very bad thing.

Have a wonder-filled week.

The Leyden Jar

Number: 
0146
Anonymous: 
Learn to construct a 25,000 volt Leyden Jar from materials found around the house. This dramatic, yet safe, demonstration is a great way to learn about electrostatics, charges, and circuits.

This project has science fair potential.


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Length: 
11:52

Finding Fat

Anonymous: 
Which foods contain fat?


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Spoon Bells

Number: 
0113
Anonymous: 
Use simple science to make spoons sound like church bells.


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thumb: 
Length: 
3:56

Bird on a Wire

Number: 
0108
Anonymous: 
How can birds sit on powerlines without being shocked?


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thumb: 
Length: 
4:28

Ice Cream Cooler

Anonymous: 
Wow! Learn about heat conduction, and eat ice cream at the same time!


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