Link to Part 1

Link to Part 2

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

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This week's experiment comes from a recent event in the science news. Researches have discovered that cats drink in a very different way from dogs and other mammals. To explore this, you will need:

- a glass of water
- your fingers
- quick reflexes

Lets start by looking at how other mammals drink. Many of them drink in the same way we do, by creating an area of low pressure inside their mouth. This lets atmospheric pressure push the water into their mouth, just as it does when you use a drinking straw or take a sip of water.

Some other mammals, such as dogs, use a different method. They curl their tongues into a spoon shape, and use it to scoop water up into their mouths.

We had always assumed that cats lapped water in the same way, but recent studies show that they use a different method. Instead of scooping the water up, the cat extends her tongue until it just touches the surface of the water. Then she pulls her tongue quickly back into her mouth. Adhesion and surface tension cause some of the water be pulled upwards, and by quickly closing her lips, the cats get a drink.

Cool, right? Want to see how it works? Place the glass of water on the table in front of you. Use the index finger of one hand to simulate a cat's tongue. You will move that finger quickly up and down, just touching the surface of the water. I found it useful to imagine I was tapping my finger quickly on a table top. As you do that, look closely to see that some of the water is being pulled upwards by the movement of your finger.

Next, use the thumb and forefinger of your other hand to simulate the cat's lips. Place your forefinger and thumb on either side of the finger that is tapping the water. As you pull your finger upwards, move the finger and thumb of the other hand together quickly, trying to catch the drops of water that follow your finger upwards. If you are fast enough, your finger and thumb will get quite wet, indicating that you would be satisfying your thirst if you were a cat.

Timing is very important, and it varies with size. Scientists calculated that larger cats would have to lap slower to be most effective, and observation of lions, tigers, and other large cats confirmed that they used the same method, and that they did lap more slowly.

I always enjoy new discoveries that have been sitting there, right under our noses, or in this case, right under out cats' noses. Scientists are already studying this in hopes of developing new ways for dealing with oil spills and delicate handling of other liquids.

Have a wonder-filled week.

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:

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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.

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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:

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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.

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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.

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Make a stream of water move without touching it.

This week's experiment came to me from my good friend Bob Cox. He told me about the trick and wanted to know why it worked. It took some thought and testing to come up with a theory of what is happening and then several e-mails to experts to confirm that I was on the right track. For this week's experiment, you will need:

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Science can be as simple as blowing bubbles in your milk.

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Learn about surface tension with a boat made out of holes.

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Herding Water

Convincing lots of little drops to join into one big one.

Last week, I left you with a question about the behavior of a stream of flowing water. I love things like this, because they are things that we see every day, and never really stop to wonder about. Once you do start to look and think, you see wonders that you never noticed before.

We were looking at a stream of water from the faucet, and noticing that as the stream fell, it got thinner and thinner. Now, why would it get thinner?

To understand that, we need to think a bit about how things fall. If you hold a ball out in front of you and drop it, it falls downwards. In the short drop to the floor, you may not notice anything else, but if the drop is longer, you will notice that as the ball falls, it is speeding up, falling faster and faster. That is because gravity continues to pull on it, so it accelerates. The acceleration of gravity is 9.8 meters per second per second. No, that second "per second" is not a typo.

What that tells us is that if you drop the ball, after one second, be falling at 9.8 meters (32 feet) per second. During the next second, it would have been accelerated by the pull of gravity to19.6 meters (9.8 + 9.8) per second. In the third second of its fall, it will be falling at 29.4 meters (9.8 + 9.8 + 9.8) per second.

The process continues, with the ball falling faster and faster, until the resistance of the air balances the acceleration of gravity. At that point, the object won't fall any faster. That is called the terminal velocity. Terminal velocity keeps raindrops from punching holes in the roof, and keeps pennies dropped from sky scrapers from making holes in the sidewalk.

So what does all that have to do with our water? Well, as the water falls, it is speeding up too. That means that the bottom part of the stream is falling faster than the top part. If we were looking at a stream of sand grains, maybe the sand falling in an hourglass, we would see that the grains of sand were very close together as they began their fall, and that they spread farther apart as they fell.

Then why doesn't the water do that? Well, water molecules are very sticky. They stick to each other very strongly, which is what causes surface tension. That keeps them from spreading out, so instead, the stream is stretched and pulled into a narrower stream, sort of like pulling on a piece of chewing gum.

As the stream of water falls faster and faster, the stream is stretched thinner and thinner. Eventually, the stretching reaches the point where it overcomes the stickiness of water, causing the stream to break up into separate water drops. You can see that by barely turning on the faucet, to create a very thin stream of water. Near the bottom of the stream, you will see it starting to break up into drops.

Sometimes it helps if you slow things down a bit, to make them easier to see. Galileo did that with the acceleration of gravity, studying balls rolling down in inclined plane instead of falling. We can do the same thing, with something thick, like a stream of chocolate syrup, falling onto a bowl of ice cream. Does it behave in the same way as a falling stream of water? You will have to try it yourself to find out. Now that is some fun homework!

Have a wonder-filled week.

This week, I will give you another challenge to ponder. Again, it is something that you have seen a million times, but probably never thought about. To try this, you will need:

- a faucet

OK, turn on the faucet, and look at the running water. Look at it carefully. Do you notice anything strange? No, it looks perfectly normal, right? Just as it always does.

Now look at the water again. Notice the size of the stream of water as it emerges from the faucet. Then follow the stream of water downwards. Is it the same size a few inches lower? No. As you get farther from the faucet, the stream of water gets smaller and smaller. How can that be? How can the stream of water get smaller?

Once again, you have a week to think about it. You are welcome to email your answers to me, or post them on my Facebook page.

Have a wonder-filled week.

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