1.1 Can You Smell What I Smell?

Getting Ready

Close your mouth and breathe in through your nose. What do you smell? Smelling is one way that your body takes in information. You take in good odors and bad odors through your nose. Most people like to smell food baking in the oven, but most people do not like the odors from their garbage.

Make a list of a few odors that you like, and a few odors that you do not like in Question a. 

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The emphasis in this reading is that all odors travel the same way—whether they smell good or bad and whether a person is familiar with the odor or not. Have students share a few responses, then point to two very different ones and ask: “Does it seem strange that X and Y both have odors that move in the same way?” 

Your list can help you think about how odors affect you. In this lesson you will read about an odor that scientists use to keep your family safe. When you finish reading, you should be able to tell why it is important to understand odors. You should also be able to tell whether all odors move in the same way.

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Smelling Odors from Across the Room

In class, you smelled materials that were in closed containers. As your teacher opened each jar, you probably did not smell anything right away. After a while, you could smell each odor. Maybe you did not even have to see the material to guess what was in the jar. People who sat closer to the jars smelled the odors more quickly than people who sat far away from the jars. Each odor had to move to reach each person’s nose.

Do All Odors Move the Same Way?

All odors move in the same way whether they are in a classroom, a house, or outdoors. All odors move away from a material and become part of the air. In this unit, you will investigate how odors move from one place to another as part of the air. Then they get to your nose. Why is this important? The next section describes a time when odor is very important to your safety.

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You Need Your Nose!

Look at your list of odors. Did you list any odors from something burning? For example, you might like the smell of burning leaves or campfires. However, if you smell something burning inside your house, that is probably not good. Odors can signal good things, or they can signal problems. Have you ever smelled spoiled milk, meat, or vegetables? Once the odor of spoiled food reaches your nose, you probably will not eat the food. Spoiled food can make you sick, so the bad odor warns you not to eat it. The odor seems to turn on an alarm in your brain that says danger.

Have you ever smelled rotten eggs? 

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Rotten eggs stink. Scientists have learned how to use rotten egg odor to keep people safe. Here is how: Human noses cannot smell natural gas. (Scientists use the word odorless to describe materials that people cannot smell.) But human noses can smell a material called mercaptan. Mercaptan has a rotten egg odor. When scientists add mercaptan to natural gas, the odor moves with the other gases that make up air.

You might have smelled mercaptan if your house uses natural gas for heating or cooking. If you have ever turned on the stove, but the burner does not light quickly, then you may have smelled the rotten egg odor. When you suddenly smell rotten eggs, you know that something is wrong. A leak of natural gas into the air can be dangerous. Scientists used their understanding of odors and how they move to make it safe for people to heat their homes with natural gas.

It Is Your Turn to Ask Questions:

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All people notice things about the world by making observations. People use their senses to see, taste, smell, touch, and hear what is around them. When people notice something, they are making observations. Sometimes people think about what they see, and they wonder about why or how something happens. Scientists do this, too. They make observations and ask questions. As an example, think about rainbows. At one time, scientists probably observed rainbows and asked questions such as, Why are rainbows always the same colors? Why do rainbows appear when it rains but not on other days? Through their questions and observations, scientists found that light from the sun enters raindrops and bends in slightly different directions. People see the bent light as colors in the shape of a rainbow.

What questions do you have about odors? 

Maybe you wonder what is moving in the air when people smell the rotten egg smell of natural gas. Maybe you wonder how scientists add odor to a material. Maybe you have a question about something on your list of odors that you like or do not like. Make a list of questions about odors that you are interested in learning the answers by investigating. (A good way to start questions is often with the word “how” or “why.”) Add these questions - more than 2 - in Question g.