Objective: The students will discover that rocks have distinguishing characteristics and that they can vary in hardness.
Subjects(s): Earth Science
Prep Time: Less than 10 minutes
Duration: 60 minutes
Materials Category: Common Household
National Education Standards
Science: 1a, 2a, 2b, 3a, 5a
Materials: Kitchen scale
Per teams of two:
Hand lens or magnifying glass
Small container of water
Supporting NASAexplores Article(s):
Visit To A Tiny Planet
Chip Off the Old Rock
Ask students to bring in two different rocks. Mark each with a dot of white correction fluid. Once it dries, write the student's initial on the dot. You also may want to bring in rocks of your own in the event that a student "forgets" or that the rocks brought in by a student do not vary enough.
This lesson will have the most benefit when students work in pairs.
Pairs are expected to work independently. For younger students, you may want to read the instructions orally as the students follow along. You may also display the Rock Worksheet on an overhead projector so that results can be easily seen by all students.
Asteroids are metallic, rocky bodies without atmospheres that orbit the Sun, but are too small to be classified as planets. Tens of thousands of asteroids congregate in the so-called main asteroid belt: a vast, doughnut-shaped ring located between the orbits of Mars and Jupiter from approximately 2 to 4 AU (300 million to 600 million kilometers or 186 million to 370 million miles). Gaspra and Ida are main belt asteroids. Known asteroids range in size from the largest at about 1,000 kilometers (600 miles) in diameter, down to the size of pebbles. Sixteen asteroids have diameters of 240 kilometers (150 miles) or greater. The majority of main belt asteroids follow slightly elliptical, stable orbits, revolving in the same direction as the Earth and taking from three to six years to complete a full circuit of the Sun.
Our understanding of asteroids has been derived from three main sources: Earth-based remote sensing, data from the Galileo flybys and laboratory analysis of meteorites. Much of our understanding about asteroids comes from examining pieces of space debris that fall to the surface of Earth. Asteroids that are on a collision course with Earth are called meteoroids. When a meteoroid strikes our atmosphere at high velocity, friction causes this chunk of space matter to incinerate in a streak of light known as a meteor. If the meteoroid does not burn up completely, what's left strikes Earth's surface and is called a meteorite.
The Earth is made of rock, from the tallest mountains to the floor of the deepest ocean. Thousands of different types of rocks and minerals have been found on Earth.
Rocks are continually changing. Wind and water wear them down and carry bits of rock away; the tiny particles accumulate in a lake or ocean and harden into rock again. By studying how rocks form and change, scientists have built a solid understanding of the Earth we live on and its long history. The rocks we see around us -- the mountains, canyons and riverbeds -- are all made of minerals.
In this lesson, students will learn how rocks differ and how to look for the differences.
Read and discuss the article orally.
Divide the students into research pairs.
Remind the students that the lens is a tool. It needs to be handled carefully. You may want to allow students a chance to practice using the lens so that they will not be tempted to play once the lesson begins.
Show the class some of the rocks that have been brought in. Tell them, "The story we read talked about asteroids and why they are studied. We leaned that they are rocks that orbit in space. They come in a lot of different sizes and shapes. The rocks of Earth come in a lot of sizes, shapes and colors, too. Some rocks are as soft as chalk, and some are as hard as diamonds. Rocks can be big or small. Today you are going to find out more about rocks."
Have each pair number their rocks from one to four. Have them draw a picture of each rock on their Student Sheets.
Instruct students to use their hand lenses and other materials to conduct tests on each of the four rocks.
Test One: Appearance: Have students write short descriptions of each rock's appearance (shape, size, texture).
Test Two: Color: Have students observe each rock's color when it is dry. Have them write the color on their Rock Worksheet. Then have them put one rock at a time into the cup of water, making sure it covers the rock. Have them observe the color of each wet rock and record it on the Student Sheet.
Test Three: Weight: Have each team sort the four rocks from heaviest to lightest. Have each pair estimate the weight of the lightest rock. Then have them record the numbers of the rocks from lightest to on the Student Sheet. Each pair will then need to weigh the rocks on a kitchen scale in grams and write the actual weight of the rock on the Student Sheet.
Test Four: Hardness. Have students give each of their rocks a scratch test to determine its hardness. Diamonds are hard; chalk is soft. Rocks can be tested for hardness by the scratch method. Rocks that can be scratched by a fingernail are considered very soft. Rocks that can be scratched by a penny are considered soft. Rocks that can be scratched with a nail are medium hard. Rocks which are not scratched by the steel nail are considered hard. Have the team try to scratch rock number one first with their fingernail.
If your rock can be scratched by a fingernail, write very soft in the box for rock one. If the fingernail did not scratch the rock, try the penny. If the penny makes a scratch, write soft. If there is still not a scratch mark, try the steel nail. If it leaves a scratch, record hard. If there is not a scratch, record very hard.
Since this can be confusing, write the following chart on the chalkboard for the students to use as a reference:
Scale / Scratched By
very soft / fingernail
soft / penny
medium / steel nail
hard / none of the above
To finish this lesson, give the students an opportunity to share what they discovered about their rocks.
Have students complete research on asteroids.