This is another of those fun bits of science that many of us think we understand until we really start to look at it. To try this, you will need:

- water
- two drinking glasses
- a saucer or cover for one of the glasses

Start by taking a glass of water outside. Find a nice, flat spot on your driveway or sidewalk, and pour out the water to make a big, wet spot. Now go for a walk, have a snack, read a chapter in your favorite book, have another snack, and then go back to look at the wet spot. Is it still there?

That will depend on the weather. If it is a very humid day, then it may still be there. If it is cold enough, your wet spot may still be there as a patch of ice. On the other hand, if it is a dry day, especially if it is warm or windy, then you will probably find that the water is all gone. Where did it go? It evaporated of course. But, what happens when a liquid evaporates?

When a substance evaporates, it changes from its liquid form to its gaseous form. Isn't that the same as boiling? But, water has to be hot for it to boil, yet it will evaporate even if the weather is near freezing. How can that be? What is the difference between boiling and evaporating?

The basic process is the same. If the molecules of the liquid have enough energy, they can break away from the rest of the group, launching themselves into the air to become a gas. The difference between the boiling and evaporating is in where the molecules get that energy.

For boiling, the energy comes from heat. Put a pot of water on the stove, turn on the heat, and soon the water molecules in the pot will gain enough heat energy to let them break away in large numbers.

But, if you take that same pot of water, and put it on the table instead, it will still evaporate. Why? Those water molecules are bouncing around, bumping into each other. When they bump, energy can be transferred from one to another, just like the balls on a pool table. If the bumped molecule is in the middle of the pot, it will probably bump into another water molecule, passing along the energy, but if it happens to be at the surface, that bump could give it enough energy to break free. It evaporated!

Notice that you did not have to heat the water to the boiling point. Even if the water is very cold, you will still have molecules at the surface that get bumped hard enough to let them evaporate.

Now, for the next step, fill two glasses half-full of water (or half-empty if you happen to look at things that way.) Put them someplace where they can stay for a few days without being in the way. Cover one with the saucer, and leave the other open.

After a few days, what do you think will happen? The water in the uncovered glass will probably evaporate away, but the water in the covered glass will still be there. Why? Does covering the glass stop the process of evaporation? No. Instead, it increases something else to balance the evaporation. Condensation.

Think back to that molecule of water that was bumped free. It is now bouncing around with the other molecules in the air. If it bounces in the right direction, it could bump back into the surface of the water. If that happens, it can stick, giving up some of its extra energy, and changing back into the liquid form of water.

In the covered glass, the water continues to evaporate just as quickly as it does in the open glass. Because the glass is closed, the number of water molecules in the air increases, meaning more and more of them will bump back into the water, changing back to a liquid. You quickly reach the point where things balance. There are just as many water molecules condensing back to water as there are evaporating into the air. So covering the glass does not stop it from evaporating. Instead, it keeps the water vapor in place, so it can bump back into the liquid again.

Now, thinking about that, why would a windy day make your water evaporate faster? If the air is still, then it is easy for a water molecule to be bumped free, rebound from an air molecule, and rejoin the water. On the other hand, if the air is moving, the water molecule may be moved away from the liquid before it bounces back. The water molecules don't leave any faster. They just have a much smaller chance of bouncing back to the liquid, so the puddle dries up faster.

Have a wonder-filled week.

Link to Part 1

Link to Part 2

The answer to Part 2, and a fun "science trick."

Your $20/year subscription helps cover the costs of producing new videos, writing curriculum units, site development, and hosting. Without that support, this site would not be possible.

If you are already a subscriber, and having problems logging in, please check the Support Page.

If you are not yet a subscriber, please check out the Free Stuff page, and Subscribe Now.

Since I have had so much fun in the Everglades, I thought we would do a related experiment this week. One of the most important things in the Everglades is water. There is a very delicate balance here, since the Everglades rely on the same water sources used by Miami and other cities, area farmers and industry. That makes it very important for people in this area to conserve water, but water conservation is important everywhere. Most people have no idea of how much water they waste every day. To give you an idea, we are going make a few tests. You will need:

- water
- measuring cups

Even little things can make a big difference in conserving water. You would be amazed how much water goes down the drain for something as simple as a dripping faucet. To see how much water this can waste, turn on the water faucet just enough to get a steady drip, drip, drip of water. Place the measuring cup under the faucet. Now wait for 15 minutes. Turn off the water and look to see how much water you collected. Multiply this by 4 and you will see how much drips away in an hour. Multiply that by 24 and you have how much drips in a day. Multiply that by 365 and you have a year's worth of drips, which is a lot of water.

Next its time to brush your teeth. Do you leave the water running while you brush? If you do, place a large bowl under the faucet when you brush your teeth. When you finish, use the measuring cups to see how much water ran down the drain while you were brushing. Multiply that by the number of times a day you brush your teeth. Then multiply that by 365 for a year's worth of tooth brushing. Again, over a year it is amazing how much water is wasted this way. Place the empty pan back under the faucet. This time, turn the water on long enough to wet the toothbrush and then turn it off. Turn it on only when you are using it. Measure to see how much you saved. Over a year, that could be a lot of water, especially if you have several people in your family.

There are many things that you can do to use water more wisely. For example, instead of pouring the water you use in these experiments down the drain, pour it on potted plants or flower beds that need water anyway. Every little bit helps. Look around your house to find all the ways that you use water. Can you figure how many gallons your family uses each day? If you look at your utility bill, you should be able to get an idea of how many gallons you use each month. Multiply that by 12 and you get an idea of how much you use each year.

Here is a math problem for you. Yes, I know that this is supposed to be science, but math plays a very large role in the world of science. Find out the population of your city. If each person in the city saved one cup of water each day, how much water would they save after one year? Yes, even small savings can add up.

It is hurricane season here in Florida, but luckily this has been a very calm season so far. We still have to be sure to be prepared, just in case. I came across the idea for this experiment while reviewing some of the emergency information. Often during hurricanes, the water supply is contaminated and it is necessary to boil your water before drinking it. All of the information sheets say that this makes the water taste flat and they give several different ways to "fix" the taste. To see how boiling changes the taste, you will need:

This experiment is Subscriber Only content.

Subscribe Now, and get full access to this experiment, and hundreds of other experiments and videos.

This is Members Only content.

Become a Member Today at the Introductory Price of
Only $20 for an Entire Year, and get full access to this site.

The Wonders of Ice

Explore why ice is one of the strangest solids we know of.

Today we actually had some much needed rain. To celebrate the rain, I thought I would do an experiment that was related to rain.

This experiment is Subscriber Only content.

Subscribe Now, and get full access to this experiment, and hundreds of other experiments and videos.

This week's experiment comes from a question that was sent to me by Hashi, one of the members of the Experiment of the Week list. She noticed that smells were stronger while taking a shower and asked why. To investigate, you will need:

This experiment is Subscriber Only content.

Subscribe Now, and get full access to this experiment, and hundreds of other experiments and videos.

Having a home at the beach, I tend to spend a lot of time building sand castles. Now while it may seem a frivolous activity, there is really quite a bit of science involved. To see some of the science of building a sand castle, you will need:

This experiment is Subscriber Only content.

Subscribe Now, and get full access to this experiment, and hundreds of other experiments and videos.

This week's experiment should be familiar to any of you that have ever cooked pancakes. As my mother taught me, and as you will find in most cookbooks, in order to tell if the skillet is hot enough for pancakes, you dip your fingers into some water and then shake a few drops onto the skillet. If the drops just sit there or if they hit the skillet and boil, then it is not hot enough. As the temperature of the skillet increases, you reach a point where the drop of water seems to bounce and glide around the skillet. Then you know that the skillet is hot enough for pancakes. This is called the Leidenfrost Effect, and that is what we want to observe now.

This experiment is Subscriber Only content.

Subscribe Now, and get full access to this experiment, and hundreds of other experiments and videos.

For this week's experiment, we are going to make a ball of oil. Don't worry, this is not nearly as messy as it sounds. You will need:

This experiment is Subscriber Only content.

Subscribe Now, and get full access to this experiment, and hundreds of other experiments and videos.

This week's experiment uses fire, so be very careful and be sure that you have an adult to help you.

This week's experiment involves both chemistry and light. It is always pleasing for me to find one experiment that can send you exploring in several different directions.

This experiment is Subscriber Only content.

Subscribe Now, and get full access to this experiment, and hundreds of other experiments and videos.

For this week's experiment, we will examine something that has caused problems for Moms throughout the ages. While washing up, someone leaves a towel hanging over the side of a sink full of water and mysteriously, the water all winds up on the floor.

This experiment is Subscriber Only content.

Subscribe Now, and get full access to this experiment, and hundreds of other experiments and videos.

When is a glass full of water really full? You may be surprised at how much you can add to a full glass without overflowing the water.

This experiment is Subscriber Only content.

Subscribe Now, and get full access to this experiment, and hundreds of other experiments and videos.

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."

This experiment is Subscriber Only content.

Subscribe Now, and get full access to this experiment, and hundreds of other experiments and videos.

This project has science fair potential.

This experiment is from a Magic of Science workshop that I taught several years ago. No, it is not a get rich quick scheme. It is a fun way to see how we can bend a ray of light.

This experiment is Subscriber Only content.

Subscribe Now, and get full access to this experiment, and hundreds of other experiments and videos.