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A. The Universe
By the end of 8th grade, students should know that:
- The sun is a medium-sized star located near the edge of a disk-shaped galaxy of stars, part of which can be seen as a glowing band of light that spans the sky on a very clear night.
- The sun is many thousands of times closer to the earth than any other star.
- Nine planets of very different size, composition, and surface features move around the sun in nearly circular orbits.
- Large numbers of chunks of rock orbit the sun.
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B. The Earth
By the end of 8th grade, students should know that:
- We live on a relatively small planet, the third from the sun in the only system of planets definitely known to exist (although other, similar systems may be discovered in the universe).
- The earth is mostly rock.
- Everything on or anywhere near the earth is pulled toward the earth's center by gravitational force.
- Because the earth turns daily on an axis that is tilted relative to the plane of the earth's yearly orbit around the sun, sunlight falls more intensely on different parts of the earth during the year.
- The moon's orbit around the earth once in about 28 days changes what part of the moon is lighted by the sun and how much of that part can be seen from the earth the phases of the moon.
- Climates have sometimes changed abruptly in the past as a result of changes in the earth's crust, such as volcanic eruptions or impacts of huge rocks from space.
- The cycling of water in and out of the atmosphere plays an important role in determining climatic patterns.
- Fresh water, limited in supply, is essential for life and also for most industrial processes.
- Heat energy carried by ocean currents has a strong influence on climate around the world.
- Some minerals are very rare and some exist in great quantities, but for practical purposes the ability to recover them is just as important as their abundance.
- The benefits of the earth's resources such as fresh water, air, soil, and trees can be reduced by using them wastefully or by deliberately or inadvertently destroying them.
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C. Processes that Shape the Earth
By the end of 8th grade, students should know that:
- The interior of the earth is hot.
- Some changes in the earth's surface are abrupt (such as earthquakes and volcanic eruptions) while other changes happen very slowly (such as uplift and wearing down of mountains).
- Sediments of sand and smaller particles (sometimes containing the remains of organisms) are gradually buried and are cemented together by dissolved minerals to form solid rock again.
- Sedimentary rock buried deep enough may be reformed by pressure and heat, perhaps melting and recrystallizing into different kinds of rock.
- Thousands of layers of sedimentary rock confirm the long history of the changing surface of the earth and the changing life forms whose remains are found in successive layers.
- Although weathered rock is the basic component of soil, the composition and texture of soil and its fertility and resistance to erosion are greatly influenced by plant roots and debris, bacteria, fungi, worms, insects, rodents, and other organisms.
- Human activities, such as reducing the amount of forest cover, increasing the amount and variety of chemicals released into the atmosphere, and intensive farming, have changed the earth's land, oceans, and atmosphere.
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D. The Structure of Matter
By the end of 8th grade, students should know that:
- All matter is made up of atoms, which are far too small to see directly through a microscope.
- Equal volumes of different substances usually have different weights.
- Atoms and molecules are perpetually in motion.
- The temperature and acidity of a solution influence reaction rates.
- Scientific ideas about elements were borrowed from some Greek philosophers of 2,000 years earlier, who believed that everything was made from four basic substances: air, earth, fire, and water.
- There are groups of elements that have similar properties, including highly reactive metals, less-reactive metals, highly reactive nonmetals (such as chlorine, fluorine, and oxygen), and some almost completely nonreactive gases (such as helium and neon).
- No matter how substances within a closed system interact with one another, or how they combine or break apart, the total weight of the system remains the same.
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E. Energy Transformations
By the end of 8th grade, students should know that:
- Energy cannot be created or destroyed, but only changed from one form into another.
- Most of what goes on in the universe from exploding stars and biological growth to the operation of machines and the motion of people involves some form of energy being transformed into another.
- Heat can be transferred through materials by the collisions of atoms or across space by radiation.
- Energy appears in different forms.
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F. Motion
By the end of 8th grade, students should know that:
- Light from the sun is made up of a mixture of many different colors of light, even though to the eye the light looks almost white.
- Something can be "seen" when light waves emitted or reflected by it enter the eye just as something can be "heard" when sound waves from it enter the ear.
- An unbalanced force acting on an object changes its speed or direction of motion, or both.
- Vibrations in materials set up wavelike disturbances that spread away from the source.
- Human eyes respond to only a narrow range of wavelengths of electromagnetic radiation visible light.
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G. Forces of Nature
By the end of 8th grade, students should know that:
- Every object exerts gravitational force on every other object.
- The sun's gravitational pull holds the earth and other planets in their orbits, just as the planets' gravitational pull keeps their moons in orbit around them.
- Electric currents and magnets can exert a force on each other.
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