There are more stars in the sky than anyone can easily count, but they are not scattered evenly, and they are not all the same in brightness or color.
Learning Goal 2
The sun can be seen only in the daytime, but the moon can be seen sometimes at night and sometimes during the day. The sun, moon, and stars all appear to move slowly across the sky.
Learning Goal 3
The moon looks a little different every day but looks the same again about every four weeks.
For Grades: 3-5
Learning Goal 1
The patterns of stars in the sky stay the same, although they appear to move across the sky nightly, and different stars can be seen in different seasons.
Learning Goal 2
Telescopes magnify the appearance of some distant objects in the sky, including the moon and the planets. The number of stars that can be seen through telescopes is dramatically greater than can be seen by the unaided eye.
Learning Goal 3
Planets change their positions against the background of stars.
Learning Goal 4
The earth is one of several planets that orbit the sun, and the moon orbits around the earth.
Learning Goal 5
Stars are like the sun, some being smaller and some larger, but so far away that they look like points of light.
Learning Goal 6
A large light source at a great distance looks like a small light source that is much closer.
For Grades: 6-8
Learning Goal 1a
The sun is a medium-sized star located near the edge of a disc-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.
Learning Goal 1bc
The universe contains many billions of galaxies, and each galaxy contains many billions of stars. To the naked eye, even the closest of these galaxies is no more than a dim, fuzzy spot.
Learning Goal 2abc
The sun is many thousands of times closer to the earth than any other star. Light from the sun takes a few minutes to reach the earth, but light from the next nearest star takes a few years to arrive. The trip to that star would take the fastest rocket thousands of years.
Learning Goal 2de
Some distant galaxies are so far away that their light takes several billion years to reach the earth. People on earth, therefore, see them as they were that long ago in the past.
Learning Goal 3
Nine planets of very different size, composition, and surface features move around the sun in nearly circular orbits. Some planets have a variety of moons and even flat rings of rock and ice particles orbiting around them. Some of these planets and moons show evidence of geologic activity. The earth is orbited by one moon, many artificial satellites, and debris.
Learning Goal 4
Many chunks of rock orbit the sun. Those that meet the earth glow and disintegrate from friction as they plunge through the atmosphere—and sometimes impact the ground. Other chunks of rock mixed with ice have long, off-center orbits that carry them close to the sun, where the sun's radiation (of light and particles) boils off frozen materials from their surfaces and pushes it into a long, illuminated tail.
For Grades: 9-12
Learning Goal 1a
The stars differ from each other in size, temperature, and age, but they appear to be made up of the same elements found on earth and behave according to the same physical principles.
Learning Goal 1b
Unlike the sun, most stars are in systems of two or more stars orbiting around one another.
Learning Goal 2ab
On the basis of scientific evidence, the universe is estimated to be over ten billion years old. The current theory is that its entire contents expanded explosively from a hot, dense, chaotic mass.
Learning Goal 2cd
Stars condensed by gravity out of clouds of molecules of the lightest elements until nuclear fusion of the light elements into heavier ones began to occur. Fusion released great amounts of energy over millions of years.
Learning Goal 2ef
Eventually, some stars exploded, producing clouds containing heavy elements from which other stars and planets orbiting them could later condense. The process of star formation and destruction continues.
Learning Goal 3
Increasingly sophisticated technology is used to learn about the universe. Visual, radio, and X-ray telescopes collect information from across the entire spectrum of electromagnetic waves; computers handle data and complicated computations to interpret them; space probes send back data and materials from remote parts of the solar system; and accelerators give subatomic particles energies that simulate conditions in the stars and in the early history of the universe before stars formed.
Learning Goal 4
Mathematical models and computer simulations are used in studying evidence from many sources in order to form a scientific account of the universe.
Learning Goal 5
As the earth and other planets formed, the heavier elements fell to their centers. On planets close to the sun (Mercury, Venus, Earth, and Mars), the lightest elements were mostly blown or boiled away by radiation from the newly formed sun; on the outer planets (Jupiter, Saturn, Uranus, Neptune, and Pluto) the lighter elements still surround them as deep atmospheres of gas or as frozen solid layers.
Learning Goal 6
Our solar system coalesced out of a giant cloud of gas and debris left in the wake of exploding stars about five billion years ago. Everything in and on the earth, including living organisms, is made of this material.
Subchapter B
The Earth
For Grades: K-2
Learning Goal 1
The temperature and amount of rain (or snow) tend to be high, low, or medium in the same months every year.
Learning Goal 2
Water can be a liquid or a solid and can go back and forth from one form to the other. If water is turned into ice and then the ice is allowed to melt, the amount of water is the same as it was before freezing.
Learning Goal 3
Water left in an open container disappears, but water in a closed container does not disappear.
For Grades: 3-5
Learning Goal 1
Things on or near the earth are pulled toward it by the earth's gravity.
Learning Goal 2a
The earth is approximately spherical in shape. Like the earth, the sun and planets are spheres.
Learning Goal 2bc
The rotation of the earth on its axis every 24 hours produces the night-and-day cycle. To people on earth, this turning of the planet makes it seem as though the sun, moon, planets, and stars are orbiting the earth once a day.
Learning Goal 3
When liquid water disappears, it turns into a gas (vapor) in the air and can reappear as a liquid when cooled, or as a solid if cooled below the freezing point of water. Clouds and fog are made of tiny droplets or frozen crystals of water.
Learning Goal 4
Air is a material that surrounds us and takes up space and whose movement we feel as wind.
Learning Goal 5
The weather is always changing and can be described by measurable quantities such as temperature, wind direction and speed, and precipitation. Large masses of air with certain properties move across the surface of the earth. The movement and interaction of these air masses is used to forecast the weather.
For Grades: 6-8
Learning Goal 2ab
The earth is mostly rock. Three-fourths of the earth's surface is covered by a relatively thin layer of water (some of it frozen), and the entire planet is surrounded by a relatively thin layer of air.
Learning Goal 2cd
Earth is the only body in the solar system that appears able to support life. The other planets have compositions and conditions very different from the earth's.
Learning Goal 3
Everything on or anywhere near the earth is pulled toward the earth's center by gravitational force.
Learning Goal 5
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.
Learning Goal 6
Climates have sometimes changed abruptly in the past as a result of volcanic eruptions or impacts of huge rocks from space.
Learning Goal 7
Water evaporates from the surface of the earth, rises and cools, condenses into rain or snow, and falls again to the surface. The water falling on land collects in rivers and lakes, soil, and porous layers of rock, and much of it flows back into the oceans. The cycling of water in and out of the atmosphere is a significant aspect of the weather patterns on Earth.
Learning Goal 8
Fresh water, limited in supply, is essential for some organisms and industrial processes. Water in rivers, lakes, and underground can be depleted or polluted, making it unavailable or unsuitable for life.
Learning Goal 9
Thermal energy carried by ocean currents has a strong influence on climates around the world. Areas near oceans tend to have more moderate temperatures than they would if they were farther inland but at the same latitude because water in the oceans can hold a large amount of thermal energy.
Learning Goal 10ab
Some material resources are very rare and some exist in great quantities. The ability to obtain and process resources depends on where they are located and the form they are in. As resources are depleted, they may become more difficult to obtain.
Learning Goal 10c
Recycling materials and the development of substitutes for those materials can reduce the rate of depletion of resources but may also be costly. Some materials are not easily recycled.
Learning Goal 11a
The wasteful or unnecessary use of natural resources can limit their availability for other purposes. Restoring depleted soil, forests, or fishing grounds can be difficult and costly.
Learning Goal 11bc
The benefits of Earth's resources—such as fresh water, air, soil, and trees—can be reduced by deliberately or inadvertently polluting them. The atmosphere, the oceans, and the land have a limited capacity to absorb and recycle waste materials. In addition, some materials take a long time to degrade. Therefore, cleaning up polluted air, water, or soil can be difficult and costly.
Learning Goal 12
The temperature of a place on the earth's surface tends to rise and fall in a somewhat predictable pattern every day and over the course of a year. The pattern of temperature changes observed in a place tends to vary depending on how far north or south of the equator the place is, how near to oceans it is, and how high above sea level it is.
Learning Goal 13
The number of hours of daylight and the intensity of the sunlight both vary in a predictable pattern that depends on how far north or south of the equator the place is. This variation explains why temperatures vary over the course of the year and at different locations.
Learning Goal 14
The earth has a variety of climates, defined by average temperature, precipitation, humidity, air pressure, and wind, over time in a particular place.
Learning Goal 15
The atmosphere is a mixture of nitrogen, oxygen, and trace amounts of water vapor, carbon dioxide, and other gases.
For Grades: 9-12
Learning Goal 1
Life is adapted to conditions on the earth, including the force of gravity that enables the planet to retain an adequate atmosphere, and an intensity of electromagnetic waves from the sun that allows water to be present in the liquid state.
Learning Goal 2
Transfer of thermal energy between the atmosphere and the land or oceans produces temperature gradients in the atmosphere and the oceans. Regions at different temperatures rise or sink or mix, resulting in winds and ocean currents. These winds and ocean currents, which are also affected by the earth's rotation and the shape of the land, carry thermal energy from warm to cool areas.
Learning Goal 3
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 difference in intensity of sunlight and the resulting warming of the earth's surface produces the seasonal variations in temperature.
Learning Goal 4
Greenhouse gases in the atmosphere, such as carbon dioxide and water vapor, are transparent to much of the incoming sunlight but not to the infrared light from the warmed surface of the earth. When greenhouse gases increase, more thermal energy is trapped in the atmosphere, and the temperature of the earth increases the light energy radiated into space until it again equals the light energy absorbed from the sun.
Learning Goal 5
Climatic conditions result from latitude, altitude, and from the position of mountain ranges, oceans, and lakes. Dynamic processes such as cloud formation, ocean currents, and atmospheric circulation patterns influence climates as well.
Learning Goal 6
The earth's climates have changed in the past, are currently changing, and are expected to change in the future, primarily due to changes in the amount of light reaching places on the earth and the composition of the atmosphere. The burning of fossil fuels in the last century has increased the amount of greenhouse gases in the atmosphere, which has contributed to Earth's warming.
Learning Goal 8
The earth has many natural resources of great importance to human life. Some are readily renewable, some are renewable only at great cost, and some are not renewable at all.
Learning Goal 9
Although the earth has a great capacity to absorb and recycle materials naturally, ecosystems have only a finite capacity to withstand change without experiencing major ecological alterations that may also have adverse effects on human activities.
Subchapter C
Processes that Shape the Earth
For Grades: K-2
Learning Goal 1
Chunks of rocks come in many sizes and shapes, from boulders to grains of sand and even smaller.
Learning Goal 2
Change is something that happens to many things.
Learning Goal 3
Animals and plants sometimes cause changes in their surroundings.
For Grades: 3-5
Learning Goal 1
Waves, wind, water, and ice shape and reshape the earth's land surface by eroding rock and soil in some areas and depositing them in other areas, sometimes in seasonal layers.
Learning Goal 2
Rock is composed of different combinations of minerals. Smaller rocks come from the breakage and weathering of bedrock and larger rocks. Soil is made partly from weathered rock, partly from plant remains—and also contains many living organisms.
For Grades: 6-8
Learning Goal 1
The interior of the earth is hot. Heat flow and movement of material within the earth cause earthquakes and volcanic eruptions and create mountains and ocean basins. Gas and dust from large volcanoes can change the atmosphere.
Learning Goal 2a
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).
Learning Goal 2b
The earth's surface is shaped in part by the motion of water (including ice) and wind over very long times, which acts to level mountain ranges. Rivers and glacial ice carry off soil and break down rock, eventually depositing the material in sediments or carrying it in solution to the sea.
Learning Goal 3
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.
Learning Goal 4
Sedimentary rock buried deep enough may be re-formed by pressure and heat, perhaps melting and recrystallizing into different kinds of rock. These re-formed rock layers may be forced up again to become land surface and even mountains. Subsequently, this new rock too will erode. Rock bears evidence of the minerals, temperatures, and forces that created it.
Learning Goal 5
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. The youngest layers are not always found on top, because of folding, breaking, and uplift of layers.
Learning Goal 6
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.
Learning Goal 7
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. Some of these changes have decreased the capacity of the environment to support some life forms.
Learning Goal 8
There are a variety of different land forms on the earth's surface (such as coastlines, rivers, mountains, deltas, and canyons).
Learning Goal 9
Matching coastlines and similarities in rock types and life forms suggest that today's continents are separated parts of what was long ago a single continent.
Learning Goal 10
The earth first formed in a molten state and then the surface cooled into solid rock.
Learning Goal 11
The outer layer of the earth—including both the continents and the ocean basins—consists of separate plates.
Learning Goal 12
The earth's plates sit on a dense, hot, somewhat melted layer of the earth. The plates move very slowly, pressing against one another in some places and pulling apart in other places, sometimes scraping alongside each other as they do. Mountains form as two continental plates, or an ocean plate and a continental plate, press together.
Learning Goal 13
There are worldwide patterns to major geological events (such as earthquakes, volcanic eruptions, and mountain building) that coincide with plate boundaries.
For Grades: 9-12
Learning Goal 1
Plants on land and under water alter the earth's atmosphere by removing carbon dioxide from it, using the carbon to make sugars and releasing oxygen. This process is responsible for the oxygen content of the air.
Learning Goal 2
The formation, weathering, sedimentation, and reformation of rock constitute a continuing "rock cycle" in which the total amount of material stays the same as its forms change.
Learning Goal 3
The outward transfer of the earth's internal heat causes regions of different temperatures and densities. The action of a gravitational force on regions of different densities causes the rise and fall of material between the earth's surface and interior, which is responsible for the movement of plates.
Learning Goal 5
Earthquakes often occur along the boundaries between colliding plates, and molten rock from below creates pressure that is released by volcanic eruptions, helping to build up mountains. Under the ocean basins, molten rock may well up between separating plates to create new ocean floor. Volcanic activity along the ocean floor may form undersea mountains, which can thrust above the ocean's surface to become islands.
Learning Goal 6
Scientific evidence indicates that some rock layers are several billion years old.
Subchapter D
The Structure of Matter
For Grades: K-2
Learning Goal 1
Objects can be described in terms of their properties. Some properties, such as hardness and flexibility, depend upon what material the object is made of, and some properties, such as size and shape, do not.
Learning Goal 2
Things can be done to materials to change some of their properties, but not all materials respond the same way to what is done to them.
For Grades: 3-5
Learning Goal 1a
Heating and cooling can cause changes in the properties of materials, but not all materials respond the same way to being heated and cooled.
Learning Goal 1b
Many kinds of changes occur faster under hotter conditions.
Learning Goal 2
No matter how parts of an object are assembled, the weight of the whole object is always the same as the sum of the parts; and when an object is broken into parts, the parts have the same total weight as the original object.
Learning Goal 3
Materials may be composed of parts that are too small to be seen without magnification.
Learning Goal 4a
When a new material is made by combining two or more materials, it has properties that are different from the original materials.
Learning Goal 4b
A lot of different materials can be made from a small number of basic kinds of materials.
Learning Goal 5
Substances may move from place to place, but they never appear out of nowhere and never just disappear.
Learning Goal 6
All materials have certain physical properties, such as strength, hardness, flexibility, durability, resistance to water and fire, and ease of conducting heat.
Learning Goal 7
Collections of pieces (powders, marbles, sugar cubes, or wooden blocks) may have properties that the individual pieces do not.
For Grades: 6-8
Learning Goal 1a
All matter is made up of atoms, which are far too small to see directly through a microscope.
Learning Goal 1b
The atoms of any element are like other atoms of the same element, but are different from the atoms of other elements.
Learning Goal 1cd
Atoms may link together in well-defined molecules, or may be packed together in crystal patterns. Different arrangements of atoms into groups compose all substances and determine the characteristic properties of substances.
Learning Goal 2
Equal volumes of different materials usually have different masses.
Learning Goal 3ab
Atoms and molecules are perpetually in motion. Increased temperature means greater average energy of motion, so most substances expand when heated.
Learning Goal 3
In solids, the atoms or molecules are closely locked in position and can only vibrate. In liquids, they have higher energy, are more loosely connected, and can slide past one another; some molecules may get enough energy to escape into a gas. In gases, the atoms or molecules have still more energy and are free of one another except during occasional collisions.
Learning Goal 4
The temperature and acidity of a solution influence reaction rates. Many substances dissolve in water, which may greatly facilitate reactions between them.
Learning Goal 5
Chemical elements are those substances that do not break down during normal laboratory reactions involving such treatments as heating, exposure to electric current, or reaction with acids. All substances from living and nonliving things can be broken down to a set of about 100 elements, but since most elements tend to combine with others, few elements are found in their pure form.
Learning Goal 6a
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).
Learning Goal 6b
An important kind of reaction between substances involves the combination of oxygen with something else—as in burning or rusting.
Learning Goal 6c
Carbon and hydrogen are common elements of living matter.
Learning Goal 7a
No matter how substances within a closed system interact with one another, or how they combine or break apart, the total mass of the system remains the same.
Learning Goal 7b
The idea of atoms explains the conservation of matter: If the number of atoms stays the same no matter how the same atoms are rearranged, then their total mass stays the same.
Learning Goal 8
Most substances can exist as a solid, liquid, or gas depending on temperature
Learning Goal 9
Materials vary in how they respond to electric currents, magnetic forces, and visible light or other electromagnetic waves.
Learning Goal 10
A substance has characteristic properties such as density, a boiling point, and solubility, all of which are independent of the amount of the substance and can be used to identify it.
Learning Goal 11
Substances react chemically in characteristic ways with other substances to form new substances with different characteristic properties.
Learning Goal 12
If samples of both the original substances and the final substances involved in a chemical reaction are broken down, they are found to be made up of the same set of elements.
Learning Goal 13
The idea of atoms explains chemical reactions: When substances interact to form new substances, the atoms that make up the molecules of the original substances combine in new ways.
For Grades: 9-12
Learning Goal 1
Atoms are made of a positively charged nucleus surrounded by negatively charged electrons. The nucleus is a tiny fraction of the volume of an atom but makes up almost all of its mass. The nucleus is composed of protons and neutrons which have roughly the same mass but differ in that protons are positively charged while neutrons have no electric charge.
Learning Goal 2
The number of protons in the nucleus determines what an atom's electron configuration can be and so defines the element. An atom's electron configuration, particularly the outermost electrons, determines how the atom can interact with other atoms. Atoms form bonds to other atoms by transferring or sharing electrons.
Learning Goal 3
Although neutrons have little effect on how an atom interacts with other atoms, the number of neutrons does affect the mass and stability of the nucleus. Isotopes of the same element have the same number of protons (and therefore of electrons) but differ in the number of neutrons.
Learning Goal 4
The nucleus of radioactive isotopes is unstable and spontaneously decays, emitting particles and/or wavelike radiation. It cannot be predicted exactly when, if ever, an unstable nucleus will decay, but a large group of identical nuclei decay at a predictable rate. This predictability of decay rate allows radioactivity to be used for estimating the age of materials that contain radioactive substances.
Learning Goal 5
Scientists continue to investigate atoms and have discovered even smaller constituents of which neutrons and protons are made.
Learning Goal 6
When elements are listed in order by the masses of their atoms, the same sequence of properties appears over and over again in the list.
Learning Goal 7a
Atoms often join with one another in various combinations in distinct molecules or in repeating three-dimensional crystal patterns.
Learning Goal 7b
An enormous variety of biological, chemical, and physical phenomena can be explained by changes in the arrangement and motion of atoms and molecules.
Learning Goal 8
The configuration of atoms in a molecule determines the molecule's properties. Shapes are particularly important in how large molecules interact with others.
Learning Goal 9a
The rate of reactions among atoms and molecules depends on how often they encounter one another, which is affected by the concentration, pressure, and temperature of the reacting materials.
Learning Goal 9b
Some atoms and molecules are highly effective in encouraging the interaction of others.
Learning Goal 10
The physical properties of compounds reflect the nature of the interactions among its molecules. These interactions are determined by the structure of the molecule, including the constituent atoms and the distances and angles between them.
Subchapter E
Energy Transformation
For Grades: K-2
Learning Goal 1
The sun warms the land, air, and water.
For Grades: 3-5
Learning Goal 1
When two objects are rubbed against each other, they both get warmer. In addition, many mechanical and electrical devices get warmer when they are used.
Learning Goal 2a
When warmer things are put with cooler ones, the warmer things get cooler and the cooler things get warmer until they all are the same temperature.
Learning Goal 2b
When warmer things are put with cooler ones, heat is transferred from the warmer ones to the cooler ones.
Learning Goal 2c
A warmer object can warm a cooler one by contact or at a distance.
For Grades: 6-8
Learning Goal 1
Whenever energy appears in one place, it must have disappeared from another. Whenever energy is lost from somewhere, it must have gone somewhere else. Sometimes when energy appears to be lost, it actually has been transferred to a system that is so large that the effect of the transferred energy is imperceptible.
Learning Goal 2
Energy can be transferred from one system to another (or from a system to its environment) in different ways: 1) thermally, when a warmer object is in contact with a cooler one; 2) mechanically, when two objects push or pull on each other over a distance; 3) electrically, when an electrical source such as a battery or generator is connected in a complete circuit to an electrical device; or 4) by electromagnetic waves.
Learning Goal 3
Thermal energy is transferred through a material by the collisions of atoms within the material. Over time, the thermal energy tends to spread out through a material and from one material to another if they are in contact. Thermal energy can also be transferred by means of currents in air, water, or other fluids. In addition, some thermal energy in all materials is transformed into light energy and radiated into the environment by electromagnetic waves; that light energy can be transformed back into thermal energy when the electromagnetic waves strike another material. As a result, a material tends to cool down unless some other form of energy is converted to thermal energy in the material.
Learning Goal 4
Energy appears in different forms and can be transformed within a system. Motion energy is associated with the speed of an object. Thermal energy is associated with the temperature of an object. Gravitational energy is associated with the height of an object above a reference point. Elastic energy is associated with the stretching or compressing of an elastic object. Chemical energy is associated with the composition of a substance. Electrical energy is associated with an electric current in a circuit. Light energy is associated with the frequency of electromagnetic waves.
Learning Goal 6
Light and other electromagnetic waves can warm objects. How much an object's temperature increases depends on how intense the light striking its surface is, how long the light shines on the object, and how much of the light is absorbed.
For Grades: 9-12
Learning Goal 1
Although the various forms of energy appear very different, each can be measured in a way that makes it possible to keep track of how much of one form is converted into another. Whenever the amount of energy in one place diminishes, the amount in other places or forms increases by the same amount.
Learning Goal 2
In any system of atoms or molecules, the statistical odds are that the atoms or molecules will end up with less order than they originally had and that the thermal energy will be spread out more evenly. The amount of order in a system may stay the same or increase, but only if the surrounding environment becomes even less ordered. The total amount of order in the universe always tends to decrease.
Learning Goal 3
As energy spreads out, whether by conduction, convection, or radiation, the total amount of energy stays the same. However, since it is spread out, less can be done with it.
Learning Goal 4
Chemical energy is associated with the configuration of atoms in molecules that make up a substance. Some changes of configuration require a net input of energy whereas others cause a net release.
Learning Goal 5
Chemical energy is associated with the configuration of atoms in molecules that make up a substance. Some changes of configuration require a net input of energy whereas others cause a net release.
Learning Goal 6
Energy is released whenever the nuclei of very heavy atoms, such as uranium or plutonium, split into middleweight ones, or when very light nuclei, such as those of hydrogen and helium, combine into heavier ones. For a given quantity of a substance, the energy released in a nuclear reaction is very much greater than the energy given off in a chemical reaction.
Learning Goal 7
Thermal energy in a system is associated with the disordered motions of its atoms or molecules. Gravitational energy is associated with the separation of mutually attracting masses. Electrical potential energy is associated with the separation of mutually attracting or repelling charges.
Learning Goal 8
In a fluid, regions that have different temperatures have different densities. The action of a gravitational force on regions of different densities causes them to rise or fall, creating currents that contribute to the transfer of energy.
Learning Goal 9
Many forms of energy can be considered to be either kinetic energy, which is the energy of motion, or potential energy, which depends on the separation between mutually attracting or repelling objects.
Learning Goal 10
If no energy is transferred into or out of a system, the total energy of all the different forms in the system will not change, no matter what gradual or violent changes actually occur within the system.
Subchapter F
Motion
For Grades: K-2
Learning Goal 1
Things move in many different ways, such as straight, zigzag, round and round, back and forth, and fast and slow.
Learning Goal 2
The way to change how something is moving is to give it a push or a pull.
Learning Goal 3
Things that make sound vibrate.
For Grades: 3-5
Learning Goal 1a
Changes in speed or direction of motion are caused by forces.
Learning Goal 1bc
The greater the force is, the greater the change in motion will be. The more massive an object is, the less effect a given force will have.
Learning Goal 2
How fast things move differs greatly. Some things are so slow that their journey takes a long time; others move too fast for people to even see them.
Learning Goal 3
Light travels and tends to maintain its direction of motion until it interacts with an object or material. Light can be absorbed, redirected, bounced back, or allowed to pass through.
For Grades: 6-8
Learning Goal 1
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. Other things that give off or reflect light have a different mix of colors.
Learning Goal 2
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.
Learning Goal 3a
An unbalanced force acting on an object changes its speed or direction of motion, or both.
Learning Goal 3b
If a force acts towards a single center, the object's path may curve into an orbit around the center.
Learning Goal 4
Vibrations in materials set up wavelike disturbances that spread away from the source. Sound and earthquake waves are examples. These and other waves move at different speeds in different materials.
Learning Goal 5
Human eyes respond to only a narrow range of wavelengths of electromagnetic waves-visible light. Differences of wavelength within that range are perceived as differences of color.
Learning Goal 6
Light acts like a wave in many ways. And waves can explain how light behaves.
Learning Goal 7
Wave behavior can be described in terms of how fast the disturbance spreads, and in terms of the distance between successive peaks of the disturbance (the wavelength).
Learning Goal 8
There are a great variety of electromagnetic waves: radio waves, microwaves, infrared waves, visible light, ultraviolet rays, X-rays, and gamma rays. These wavelengths vary from radio waves, the longest, to gamma rays, the shortest.
For Grades: 9-12
Learning Goal 1
The change in motion (direction or speed) of an object is proportional to the applied force and inversely proportional to the mass.
Learning Goal 2
All motion is relative to whatever frame of reference is chosen, for there is no motionless frame from which to judge all motion.
Learning Goal 3a
When electrically charged objects undergo a change in motion, they produce electromagnetic waves around them.
Learning Goal 3c
In empty space, all electromagnetic waves move at the same speed—the "speed of light."
Learning Goal 4
Whenever one thing exerts a force on another, an equal amount of force is exerted back on it.
Learning Goal 5ab
The observed wavelength of a wave depends upon the relative motion of the source and the observer. If either is moving toward the other, the observed wavelength is shorter; if either is moving away, the wavelength is longer.
Learning Goal 5c
Because the light seen from almost all distant galaxies has longer wavelengths than comparable light here on Earth, astronomers believe that the whole universe is expanding.
Learning Goal 6ab
Waves can superpose on one another, bend around corners, reflect off surfaces, be absorbed by materials they enter, and change direction when entering a new material. All these effects vary with wavelength.
Learning Goal 6c
The energy of waves (like any form of energy) can be changed into other forms of energy.
Learning Goal 7
In most familiar situations, frictional forces complicate the description of motion, although the basic principles still apply.
Learning Goal 8
Any object maintains a constant speed and direction of motion unless an unbalanced outside force acts on it.
Subchapter G
Forces of Nature
For Grades: K-2
Learning Goal 1
Things near the earth fall to the ground unless something holds them up.
Learning Goal 2
Magnets can be used to make some things move without being touched.
For Grades: 3-5
Learning Goal 1
The earth's gravity pulls any object on or near the earth toward it without touching it.
Learning Goal 2
Without touching them, a magnet pulls on all things made of iron and either pushes or pulls on other magnets.
Learning Goal 3
Without touching them, an object that has been electrically charged pulls on all other uncharged objects and may either push or pull other charged objects.
For Grades: 6-8
Learning Goal 1
Every object exerts gravitational force on every other object. The force depends on how much mass the objects have and on how far apart they are. The force is hard to detect unless at least one of the objects has a lot of mass.
Learning Goal 2
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
Learning Goal 3
Electric currents and magnets can exert a force on each other.
Learning Goal 4
Electrical circuits require a complete loop through which an electrical current can pass.
Learning Goal 5
A charged object can be charged in one of two ways, which we call either positively charged or negatively charged. Two objects that are charged in the same manner exert a force of repulsion on each other, while oppositely charged objects exert a force of attraction on each other.
For Grades: 9-12
Learning Goal 1
Gravitational force is an attraction between masses. The strength of the force is proportional to the masses and weakens rapidly with increasing distance between them.
Learning Goal 2a
Electric forces acting within and between atoms are vastly stronger than the gravitational forces acting between the atoms. At larger scales, gravitational forces accumulate to produce a large and noticeable effect, whereas electric forces tend to cancel each other out.
Learning Goal 2b
At the atomic level, electric forces between electrons and protons in atoms hold molecules together and thus are involved in all chemical reactions.
Learning Goal 2c
Electric forces hold solid and liquid materials together and act between objects when they are in contact—as in sticking or sliding friction.
Learning Goal 3
Most materials have equal numbers of protons and electrons and are therefore electrically neutral. In most cases, a material acquires a negative charge by gaining electrons and acquires a positive charge by losing electrons. Even a tiny imbalance in the number of protons and electrons in an object can produce noticeable electric forces on other objects.
Learning Goal 4ab
In many conducting materials, such as metals, some of the electrons are not firmly held by the nuclei of the atoms that make up the material. In these materials, applied electric forces can cause the electrons to move through the material, producing an electric current. In insulating materials, such as glass, the electrons are held more firmly, making it nearly impossible to produce an electric current in those materials.
Learning Goal 4c
At very low temperatures, some materials become superconductors and offer no resistance to the flow of electrons.
Learning Goal 4d
Semiconducting materials differ greatly in how well they conduct electrons, depending on the exact composition of the material.
Learning Goal 5ab
Magnetic forces are very closely related to electric forces and are thought of as different aspects of a single electromagnetic force. Moving electrically charged objects produces magnetic forces and moving magnets produces electric forces.
Learning Goal 5c
The interplay of electric and magnetic forces is the basis for many modern technologies, including electric motors, generators, and devices that produce or receive electromagnetic waves.
Learning Goal 6
The nuclear forces that hold the protons and neutrons in the nucleus of an atom together are much stronger than the electric forces between the protons and electrons of the atom. That is why much greater amounts of energy are released from nuclear reactions than from chemical reactions.
Learning Goal 7
Electric currents in the earth's interior give the earth an extensive magnetic field, which we detect from the orientation of compass needles.
Learning Goal 8
The motion of electrons is far more affected by electrical forces than protons are because electrons are much less massive and are outside of the nucleus.
