QUESTION

Does air take up space?

MATERIALS

Balloon (minimum 9 inches)

Glass bottle with a small mouth

Pot of boiling water

Pot of ice water

Funnel

Masking tape

Water

PROCEDURE

• Place the mouth of the balloon over the mouth of the bottle. It should hang limply at the side of the bottle.

• Make sure the balloon makes a good seal around the top of the bottle and gently place the bottle into the pot of boiling water. Be careful not to stand too close to the boiling water. Observe the changes in the balloon.

• Remove the bottle from the hot water, remove the balloon, then replace it over the mouth of the bottle. The bottle now contains very hot air.

• Place the bottle into the pot of ice water and observe the changes in the balloon.

• Remove the bottle from the water and let it sit at room temperature for 10 minutes.

• Remove the balloon from the top of the bottle.

• Place the funnel in the mouth of the bottle and tape the mouth of the bottle to the funnel so that no air can escape.

• Pour water into the funnel and watch what it does.

WHAT'S HAPPENING

Air definitely takes up space! When you first put the balloon on the bottle, you “captured” the air that was in the bottle. It didn't inflate the balloon because it fit nicely into the bottle. When you heated it up, however, the air expanded and took up even more room. The only place it could go was into the balloon, so the balloon inflated. When you removed the bottle from the hot water and placed it into the ice water, the air was compressed. Not only did it not inflate the balloon, it pulled the balloon down into the bottle. When you returned the bottle to its original temperature, the balloon should have returned to its original size, shape, and location.

The funnel experiment shows that air takes up room and can't easily be squeezed. When you sealed the top of the bottle, you gave the air nowhere to go. So when you poured the water into the funnel, it wasn't heavy enough to compress the air in the bottle and it remained in the funnel, apparently defying gravity.

FOLLOW-UP

Can you think of other examples of air expanding or contracting that you might encounter?4

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KIDS' LAB LESSONS

QUESTION How can you use the sun to tell time?

EXPERIMENT OVERVIEW In this experiment you'll get to build your own sundial. With it, you can keep time the way ancient civilizations did. As the sun rises and sets, it makes shadows of different lengths and angles. You'll use the location of the sun's shadow on your sundial to tell you exactly what time it is.

SCIENCE CONCEPT The sun doesn't actually move around the earth; it only seems that way. Instead, the earth rotates on its axis, so at any one time about half the people on Earth can see the sun and the other half cannot. This is how we get night and day. What a sundial does is track the location of the shadow that the sun makes, and it uses that location to determine the time of day. You have to know a few things in order for your sundial to work. For example, you need to know where true north is, and you need to know where the sun's shadow will be at certain times of day. Once you have set up your sundial, you should find it to be pretty accurate!

MATERIALS

Sturdy paper plate

Unsharpened pencil

Modeling clay

Compass

Marking pen

PROCEDURE

• Poke a hole in the middle of the paper plate large enough for the pencil to fit through.

• Stick the pencil through the plate. Make sure the bottom of the plate is facing up.

• Place the end of the pencil in a lump of clay below the plate to anchor it down.

• Use the compass to locate true north and place your sundial in an open space with the pencil pointing slightly to the north. (This method works for anyone who lives in the Northern Hemisphere. If you live in the Southern Hemisphere, you will point the pencil to the south.)

• 5. At 8:00 in the morning, mark on the sundial the location of the pencil's shadow. Label it “8:00 A.M.” Repeat this step every two hours until sunset. Your sundial is ready!

QUESTIONS FOR THE SCIENTIST

• Are the markings evenly spaced?____________________________

• Do you think it matters what time of the year you build or use your sundial? What happens when the days get longer or shorter?_______________________

• At what time of day does the shadow of the sun point true north? Is it this way all year round?______________________________________________

FOLLOW-UP Research some of the civilizations that used sundials and think about these questions:

• What were some of the variations they built?

• Were any of them like yours?

• Why do you think people stopped using sundials?

Look around your town to see of you can find any sundials. Check the accuracy of any you find.