Hands-on science

Check out these hands-on experiment after you've read "Shark-Bite Science" (p. 13) and "Could You Survive the Tropics?" (p. 16). They're fun and foolproof!

SUCTION SCIENCE

You learned in "Shark-Bite Science" that the blind shark uses suction to latch onto prey. Discover the strengths of different-size suction cups.

YOU NEED:

1 small suction cup (with hook) * 1 large suction cup (with hook) * water (for wetting the suction cups) * 1 plastic grocery bag * medium-size textbooks (5 or 6) * paper and pencil * balance * graph paper

TO DO:

1. Wet the back of a small suction cup and press it onto a flat vertical surface, like a locker.

2. Hang the grocery bag by one handle on the suction cup's hook.

3. Place one textbook into the hanging bag. Continue to add books (one at a time) until the suction cup releases from the surface and falls.

4. Weigh the books in the bag (not including the last book that made the suction cup fall).

5. Repeat Steps 1 to 4 using the large suction cup.

6. Make a bar graph showing the weight each suction cup held.

CONCLUSIONS:

Which size suction cup held the most books before falling? Why? Explain how the suction cups are similar to the blind shark's feeding method.

DON'T STOP NOW!

Research to find out how suction cups work.

S.O.S.

In "Could You Survive the Tropics?" you read that a CD can reflect sunlight to signal an airplane for help. Find out which materials best reflect light.

YOU NEED:

1 sheet colored construction paper * tape * flashlight * CD * 1 sheet black construction paper * glass jar (about 10 ounces) * aluminum foil (15 cm by 15 cm, or 6 in. by 6 in.) * small mirror * paper and pencil

TO DO:

1. Divide into groups of three students.

2. Turn off the lights in the room.

3. Tape a sheet of colored construction paper to the wall at eye level.

4. Have one student (back facing the wall) shine a flashlight toward another student holding a CD.

5. Have the student holding the CD move it until light from the flashlight bounces off it and appears on the colored paper.

6. Have the third student record what you see on the paper (for example, how bright is the light?).

7. Repeat Steps 4 to 6 using the following materials instead of the CD: black construction paper, glass jar, aluminum foil, and a mirror.

CONCLUSIONS:

What caused the CD to light up a spot on the hanging paper? Which material resulted in the brightest light appearing on the hanging paper? The dimmest? Why?

ANSWER

Suction cups work because of air pressure. At sea level, atmospheric pressure (force exerted by the atmosphere) constantly pushes down on Earth at about 6.7 kilograms (14.7 pounds) per square inch. Pressing a suction cup against the flat surface forces air out of the space under the suction cup. Because the atmospheric pressure pressing down on the suction cup is greater than the air pressure inside the cup, the surrounding air pressure holds the suction cup in place.

The larger suction cup held more weight. That's because there is more over which atmospheric pressure can push. A larger area means more pressure is holding the large suction cup to the flat surface.

When a blind shark pumps water into its mouth and out its gills, it creates a lower pressure inside its body--like the bottom side of a suction cup. The higher pressure outside the body pushes the shark's prey into its mouth.

S.O.S.

The CD is reflective, meaning Chat light waves bounce off its surface onto another surface. Results may vary depending on how dim it is in the classroom and the brightness of the flashlight. Generally, mirrors have a high reflectivity and will give the brightest results. The dimmest: black paper and glass. That's because black paper absorbs light rays, therefore it is not very reflective. Also, glass is not a good reflector; the light will pass through the glass surface of the jar.

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