Hot News!

Here's a heat-related story that has been in the news lately, and you can do an experiment to see if it is true. Dr. Steven Chu, the U. S. Secretary of Energy, said that Americans could save a lot of energy by making the roofs of their houses white and/or shiny, and by paving roads with light-colored concrete instead of black asphalt. Does the color of the roof really matter?

You should do this experiment on a bright sunny day. You'll need a thermometer, a box large enough to hold the thermometer (about as big as a shoe box), and some materials for the "roof", like white paper, black paper, aluminum foil, or anything else you want to try. You can decorate the box with a door and some windows to make it look more like a house, but the experiment will work even if you don't do this.

Put the thermometer in the box, then place the roofing material flat on top of the box. Check the temperature and write it down. Place the box in the sun for one hour, then record the temperature again. Try all the different materials. Keep an eye on the weather, because if the sun isn't equally strong for all the roof tests, your results might not be correct. Which type of roof resulted in the coolest house? What does this tell you about which roof would be best in the summer?

Now, before you go and paint your roof white, ask yourself some more questions - which type of roof would be best in the winter, when you want your house to be warm and toasty? What is the climate like where you live? Is it really cold in the winter? Is it really hot in the summer? How long does the cold weather last, and how long is the hot season? So, the answer to whether a white or shiny roof would help you save energy over a whole year depends a lot on where you live. That's the way it often is with suggestions about saving energy - there's no easy answer that works for everyone!

Where Does Heat Come From?

When we talk about "hot" weather, we are referring to heat that comes from the sun. The sun's heat is created by nuclear fusion, in which hydrogen atoms transform into helium. What other sources of heat can you think of? In the winter, we usually heat our homes by burning a fuel, like oil, natural gas, or wood; this is a chemical reaction called combustion. You've probably also noticed that some electrical appliances, such as lamps and toasters, also get hot. The sun, oil, electricity - these seem to be very different. How can they all produce the same thing - heat?

You might think that they all contain heat, which just escapes when fusion, combustion, or electricity happens. Long ago, scientists believed that matter contained phlogiston (pronounced flow-jis-tun), a substance that had no taste, color, or weight. They thought that phlogiston came out of matter when it burned. There were a lot of problems with this idea, and by around 1800, scientists realized that phlogiston didn't really exist.

So, matter doesn't contain either phlogiston or heat, but it does contain thermal energy. "Heat" and "thermal energy" may sound like they mean the same thing, but to scientists, they don't. This might be easier to understand by a comparison. Think of the aroma of cookies baking in the oven. Where does the smell come from? "Smell" isn't something that the cookie dough releases as it cooks. Instead, we smell that wonderful odor when our nose senses certain molecules given off by the cookies. So, smell isn't something in itself, but it is what we experience. Usually, when we say that something is "hot", we mean that it feels warm to the touch. Thermal energy is sort of like the fragrant molecules. When it is released, we feel its effect, and call it heat. Of course, they're not exactly the same, because thermal energy doesn't contain actual molecules, but hopefully you get the idea.

When you burn wood, the fire feels hot because the original wood has more thermal energy that the ashes, water, and other stuff that's left over after the fire. The heat you feel is the thermal energy that is lost during combustion. The same thing happens during the fusion reactions in the sun. You can also feel heat when some other type of energy is transformed into thermal energy. That's why electricity creates heat - the electrical energy is changed into thermal energy. In the next experiment, you'll learn how to turn mechanical energy into thermal energy - using your very own hands!

Hot & Cold

We all know when something feels hot or cold, but did you ever think about what causes it to feel that way? You probably know that everything is made up of molecules, which tiny bits of matter. When something feels hot, it means that the molecules are moving very fast. So, how do the molecules move when something is cold? That's right - they're slow.

Now, you might think that you could never see how fast molecules move. After all, they're really tiny, and your eyes aren't that good! But you can do an experiment that will let you see the effect of their motion. Here's what you need:

2 drinking glasses of the same size and shape
Food coloring
Hot water (from the faucet is OK, but make sure you don't get scalded)
Cold water (also from the faucet)

Fill one glass with hot water. Fill the other glass to the same level with cold water. Add 3 drops of food coloring to each glass. Watch for a few minutes. What do you see? Can you explain your results based on the different speeds of the molecules in hot and cold water?

Summertime Science!

It's been pretty cool in the Northeastern US so far this summer, but the heat and humidity will be here soon! We'll be talking about heat over the next few weeks, and will give you a bunch of hot experiments that you can try at home! As always, be sure to follow the instructions carefully, and make sure that adults are around when you are doing any experiments.