Hands On Physics
Where does the smoke from fires, volcanoes, and vehicles go? What about
dust clouds, sand storms? You can see smoke rise from a fire and appear
to vanish. Dust clouds eventually dissipate. These clouds seems to vanish
in the air, but that is often just an illusion. Smoke and dust spread out
in the air so you cannot see them but some particles remain to cause haze.
Small particles can stay suspended in air for very long times. The larger
particles fall to earth, but particles that are small enough fall so slowly
that they are effectively part of the air. This is where haze comes from.
The Story: Introduction
Scientists don't know enough about haze. They want to know how much there
is each day, where it originates, and how long it lasts in the atmosphere.
Here are some examples of why more haze information would be helpful:
Forrest Mims has noticed an increase in diseases when
there is haze. He thinks that ultraviolet light that has a disinfectant
effect because it can kill bacteria and mosquito larvae. So haze, which
blocks ultraviolet light, interferes with the natural disease prevention
of ultraviolet light.
Rudi Hasar is interested in haze itself. He wants to know whether
it is increasing, where it goes, and how long it lasts. As the ozone layer
is being depleted, we should be exposed to more ultraviolet light, but this
is not observed. Rudi thinks this is because haze levels are increasing,
Many scientists use satellite pictures of the earth in their studies. When
the earth is obscured by haze, they cannot extract as much information from
satellite pictures. If only they knew how much haze there was in their pictures,
they could compensate. But no one collects day-by-day haze data over land.
So, many of those expensive satellite photographs cannot be fully used.
You can help these and other scientists by building an instrument
to measure the amount of haze where you are. Use this instrument to take
regular observations and sent your data to the International Haze Database.
Students and amateur scientists all over the world are building these photometers
and contributing data. Soon, we hope to build a worldwide network of volunteers
This instrument is called a sun photometer because it measures how bright
the sun appears.
By the end of this unit, you should be able to:
Questions to Think About:
- describe how haze influences light of different wavelengths.
- accurately measure the amount of haze in your atmosphere
- contribute accurate haze data to an international haze database.
- Why measure haze in the first place?
- How does haze effect the transmission of sunlight?
- What is the meaning of the follow terms and why are they important
in the study of haze:
- light intensity
- frequency of light
- Can you determine the thickness of the atmosphere?
- What can be used to measure intensity of sunlight.
- How can you amplify (magnify) weak electrical signals?
Learn by Doing
Most people learn concepts by making things and then thinking about them.
Too often students try to jump ahead and memorize the equations and definitions
without giving themselves time to think. This is why Hands On Physics units
emphasize "hands on" building.
Use the HOP Structure
There are three major sections to all HOP units: "messing around,"
"core project," and "extensions." The "messing
around" part is a chance to learn the big physics concepts without
worrying about a lot of details and computations. The "core project"
is an extended construction project that everyone does. Then you choose
one of a number of "extensions" to work on. Try "Messing
Around" to get a feeling for what happens during a bungee jump. After
you learn how to measure the short times involved, work through the core
project and then choose an extension.
Think in the Lab
It is important that you use your mind while you are in the lab doing these
various projects. You cannot just follow the directions and fill in the
blanks. We don't tell you every little step because you should be learning
how to do things yourself. Eventually, we want you to be able to undertake
an entire project. To get to this level, you have to make larger and larger
steps without help.
Fill in the Gaps
You may find this frustrating. You may get mad at the instructions that
seem vague and you may wish your teacher could help you all the time. But
before asking for help, talk it out in your group; try to invent a way out
of your problem. If you are not sure whether you are doing the "right
thing", write down what your problem was and what you decided.
Do Your Own Thing
There will be times when you think of a better way to do something than
in our directions. You may find it difficult to get the materials we use
or my may have better materials. GREAT. Do it your way. Just be sure you
understand why we did it our way and make sure your way accomplishes the
same goals. If yours is really better, tell us about it. Write it up and
send it to our discussion list. Help us make HOP better together.
Make Mistakes Rapidly
Remember, it is okay to make mistakes; we learn from our mistakes. Always
think about safety and try to avoid breaking things. But if you make a mistake,
don't be discouraged; just try again. The more mistakes you make, the more
you must be learning.
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