Monthly Archives: February 2013

How Do Ice Cubes Work?

It seems like a simple question, with a simple answer: “The water gets colder!” But why? And what do we mean by “colder?”

Water (like just about everything else) can exist as a solid, a liquid, or a gas. The difference is its level of energy. If you add thermal energy – also known as “heat” – to an ice cube, it will melt into a liquid and you can drink it. But if your thirst for knowledge exceeds your thirst for water, you could keep on adding energy to the water just to see what happens. Of course you know what will happen – after adding enough energy, the liquid water will boil and turn into a gas. These phase changes – melting and boiling – happen to pure water at 0°C/32°F and 100°C/212°F.

If you are a student like most of my readers, you may be wondering why the amount of energy in a substance determines its state of matter – solid, liquid, or gas. This is because energy makes the molecules in a substance vibrate. If they have less energy, they will not vibrate very much, and the substance will be in a solid state. More energy means more vibration; at some point the substance will be vibrating too strongly for it to keep its shape, and it will melt. Likewise, the boiling point is the amount of energy at which the vibration is too strong for the substance to stick together, and it becomes a gas.

We measure the amount of thermal energy in units called “degrees”. When we talk about cooking food at 350°, or about the temperature outside being 45°, we are describing the amount of thermal energy in the food, or in the air.

Now we can deal with the question of how an ice cube cools a glass of water. The water in the ice cube is a solid, so it has less energy than the liquid water in the glass. When you drop a few ice cubes into the glass of water, they absorb some of the energy in the water. The ice gets the same amount of energy that the liquid water loses. As the ice melts, the water cools. Putting a little ice in a large glass of water will melt the ice quickly without cooling the water much; but adding a cupful of ice to a small amount of water might freeze the water. It depends on how much or how little energy is in either substance.

If you perform this experiment at home, try putting a thermometer in the glass before you begin. Measure the water temperature before adding the ice, and again after the ice melts. The change in degrees is the amount of thermal energy absorbed by the ice!

Cool.

Another New Trick

So this weekend will be the second one I have spent on Codecademy learning some programming skills. How did this happen to me? A year ago, I did not even have a blog! My computer was a tool for e-mail and reading the news and checking the weather! I guess I had an “aha!” moment. After switching out the operating system on my computer, I felt very proud of myself for about half an hour. Then when the glow wore off, I realized I had a lot of work to do. I always knew there is a lot going on beneath the surface of computer applications – I once translated the user’s manual for a business management software system – but I never felt like programing was something I could learn to do. After successfully doing one small bit of computer alteration for the first time, I started to feel like it might be doable. So I got started! Codecademy is a site where you can get free lessons and practice in several programming formats. It’s fascinating. I have learned a tiny bit about how to cause some of the effects I enjoy about computers, like being able to search a database and make little colored circles move around by clicking on them. More importantly, I am being reminded that it is never too late to learn something new, and that knowledge is power, and so learning new things adds to your freedom of choice.

Never stop learning!

Do Things Really Look Different From "Down Under"?

I wish I could answer this question from experience. When I was ten years old, a neighbor lent me a book called The Complete Adventures of Blinky Bill – Blinky Bill was a koala – , and I fell in love with Australia. It would be truer to say I fell in love with the stories about Blinky Bill and his marsupial friends, because they were all I knew about Australia. It’s a good book. It made me want to go off and explore Australia immediately – a desire which, regretfully, I have never had the opportunity to indulge. Still, the Land Down Under has always had a special place in my imagination since then.

Most of us have heard that water goes down the drain one way (counterclockwise) in the Northern Hemisphere and the opposite way (clockwise) in the Southern Hemisphere. This is supposed to be due to the Coriolis Effect. To be very brief, the Coriolis Effect is the way the Earth’s rotation makes large bodies of fluids – like water and air in the oceans and the atmosphere – start to spin. The Coriolis Effect is what causes hurricanes to form. But it does not affect the way water goes down a drain in either hemisphere. The amount of water in a bathtub or toilet is too small to be affected by Coriolis forces. You can prove this yourself by filling the sink a few times and watching it drain. Sometimes the water will start to rotate, and sometimes it will just drain away with no spinning motion at all. You can run a finger around the drain clockwise to start a clockwise rotation, or make it drain counterclockwise if you like. It will not change due to the Coriolis Effect.

Tropical cyclone storms are another matter. These rotating storm systems (called “hurricanes” around the Americas and “Typhoons” around Asia) form because of the Coriolis Effect, and they turn counterclockwise in the Northern Hemisphere and clockwise south of the equator. The huge amounts of air and water involved are affected by Coriolis forces, unlike draining water in a sink or tub.

What else looks different in the Southern Hemisphere? If you watch the moon change phase throughout its cycle, you will notice that the change happens from right to left. (Click here for a really good animated model.) In the Southern Hemisphere, the pattern is reversed: the phases change from left to right! This would seem very strange to me. Maybe someday I will get to visit Australia and find out for myself!

Another thing that looks different from the Southern Hemisphere is the starry night sky. Since the Southern Hemisphere looks out on space in the opposite direction from the Nothern Hemisphere, the field of vision is completely different. Near the equator, the view from either hemisphere is most similar, but the difference increases the farther you go toward either pole. (Click here for a great map of the stars from both hemispheres.)

It will never be the same to see something online as it would be to see it with your own eyes. I have always enjoyed traveling and hope to keep discovering and exploring new places as long as I live. St Augustine once said, “The world is a book, and those who do not travel read only a page.” How true.

How Do We Know the Distance to Far-Away Galaxies?

If you read my post about Hubble’s Law, you may be asking “How did Hubble know the fastest-moving stars were farther away?”

That is a good question, and it means I am going to have to explain something called “parallax”. Parallax is the difference in the way an object looks from two different points of view. It is easy to observe parallax. Close one eye and look at something close to you, like the computer monitor or an object you can reach. Now quickly close that eye and open the other. Switch eyes like this a few times in rapid succession. The object you are looking at seems to jump back and forth. Of course it isn’t really moving – your eyes are a few centimeters apart, so each eye sees a slightly different view. Now look at something a little farther away, maybe across the room, and repeat the experiment. The object still seems to jump, but not as much. Next, go outside. Look at the farthest object you can see: trees on the horizon, mountains if you have any to look at, the moon if it is visible. Do the eye thing again. The object may not seem to move at all. You have just discovered parallax rangefinding.

With highly sensitive scientific instruments, we can detect parallax even with very distant objects. The difference in the appearance of a galaxy in spring and autumn (when Earth is at two different points separated by about 300,000,000 kilometers along its orbit) makes distant galaxies “jump” a little when the images taken are compared, just like the objects you experimented with. By analyzing the parallax, the galaxies’ distance can be calculated.

Together with Hubble’s Law, parallax allows us to describe the size and movement of our universe.

How Do We Know That the Universe Is Expanding?

The answer to this question is connected to Hubble’s Law: all the things we can observe in deep space – stars, nebulae, galaxies, and everything else – show a redshift, or Doppler shift, proportional to their distance from us (or from each other). Since you are reading this article, I am going to assume you do not know about Hubble’s Law, or the Doppler Effect, so I will do my best to explain those concepts.

The Doppler Effect is what you hear when a fast-moving, noisy object passes by. If a car went by at 160 kilometers (100 miles) per hour and the driver was leaning on the horn the whole time, you would notice that the horn would suddenly start to drop in tone as the car passed you. This is because sound waves do not travel that much faster than a speeding car – only about 1100 kilometers (720 miles) per hour. As the car speeds away from you, the sound waves get “stretched out”, and longer wavelengths make a lower tone. The first time this was explained scientifically was in 1842 by an Austrian scientist named Christian Doppler, which is why we call it the Doppler Effect.

The Doppler Effect works for light waves too, but we don’t notice it all around us on Earth because light travels so fast (300,000 kilometers / 186,000 miles per SECOND) that nothing on Earth is far enough or fast enough to make it change colors by the Doppler Effect. Distant stars and galaxies are a different matter. They are very far away, and moving very fast. The farther away they are, the more their light is “stretched” to a longer wavelength, which makes them appear redder (this is called “redshift). The American astronomer Edwin Hubble observed this by watching many stars through a telescope. Other scientists had predicted that the universe is expanding, but Hubble was the one who proved it. Before Hubble, we didn’t even know there was a universe beyond the Milky Way galaxy. Even astronomers thought that the blurry objects in the telescope were nebulae, clouds of space gas. After Hubble’s discovery, they started to realize that there were many other galaxies quite like the Milky Way, deep out into a universe that was far bigger than anyone had imagined.

Maybe the best model for the expanding universe is to take a light-colored balloon and make a few small dots on it with a Sharpie. Ask someone to blow it up, and watch what happens to the dots as the balloon inflates. The dots that are farthest apart will move away from each other faster than the ones that are closest together.

Our country honored Edwin Hubble by naming the first orbiting telescope after him. Since 1990, the Hubble Space Telescope has given us the clearest and most beautiful pictures of distant galaxies and other objects in deep space.

Does Water Evaporate When the Sun Isn't Shining?

Everybody knows how quickly a puddle of water evaporates from the sidewalk on a hot summer day. But does water evaporate at night, or when it’s cool and cloudy?

Let’s look at what evaporation is. Liquids can change states of matter and become gases by absorbing energy. This can happen in two ways. If the entire liquid is heated (like a pot of water on the stove, the molecules throughout the liquid move faster and separate, forming bubbles of gas. If you watch water heating in a pot, you will notice that the bubbles come from the bottom of the pot because that is the part closest to the heat source. We call this “boiling”.

Evaporation is different. It only happens at the surface, where the liquid comes into contact with air; being a gas, the air has a higher level of energy, which the liquid can absorb. This happens not because of the presence of air, but because of the higher energy level at the surface. On the Moon, for example, there is no liquid water. There is water ice in some of the deep craters where the Sun never shines; the temperature here is about -249°C (-416°F), far below the freezing point of water (and most other substances as well). But if you could stand in such a crater and kick a lump of ice into the sunlight, it would not melt; the strong radiation from the Sun – without any atmosphere to reduce its glare – would vaporize the ice immediately.

So water evaporates at night, and in the shade, as long as the temperature is above freezing (0°C / 32°F). But it evaporates faster the higher the temperature is, and very slowly if it is cold.

Is a Virus a Living Creature?

I suppose the answer to this question depends on how you define a “living creature”. This is not as simple as it seems: the more we learn about living things, the harder it has become to come up with a definition of life that holds true in every case. Anyone can compare a squirrel to a stone and pick out the living creature. But what if you were exploring an alien planet and came upon a thing you had never seen before? How would you know if it were alive or not? Without actually touching them, would you be able to tell an egg from a stone carving of an egg? At first glance, a hibernating animal seems very much like a dead one. Bacteria are living things, but are too small to see without a microscope; nobody knew of their existence until 1676, less than 400 years ago. Viruses, which are even smaller, were discovered only a little more than one hundred years ago, in 1898. You can’t tell whether something is alive if you can’t even see it!

What is life? Biologists agree that there are several signs that a thing is living. Using energy, growing, having organized structure (that is, at least one cell), responding and adapting to the environment, and reproducing are all things that living creatures do. Not all biologists agree about how many of these behaviors are needed to call something alive. For example, even a rock crystal grows – but it does not behave in any of the other ways living things do, and it is not alive.

So what about a virus? Viruses are not cells – they are simple packages of genes with no cell parts. They reproduce, but they need to get inside a host cell – a living creature – in order to take over the cell’s functions, re-programming it to make more viruses. A virus adapts to environmental change (which is why we need a new flu vaccine every year). But it does not use energy for its inner processes, because it has no inner processes.

Some biologists look at all these traits and decide that a virus is a living thing. Others prefer to call viruses “semi-living”, because they have some characteristics of living organisms but lack many other important ones.

Viruses are interesting because they make us think about what life is exactly. It seems there is less of a clear line between living and non-living than we used to think!