Defining and Describing Position

Transcription

1 Defining and Describing Position 8.1.a, page 2 1. Choice D is correct. The person s location is compared to Los Angeles. Choices A, B, and C are incorrect. Although distances and directions help describe locations, neither is a reference point. 2. Choice C is correct. East and south are standard directions. Choices A and B are incorrect, as they are distances. Choice D is incorrect, because the school is a reference point, not a direction. 3. Choice A is correct. A standard reference point is a location people agree to use as a reference point. Choices B and C are not correct because reference points are not distances or directions. Choice D is not correct because a standard reference point is a point that is agreed upon, not just any point. 4. Choice B is correct. The positions of the three other objects are described relative to the stop sign. Therefore, the stop sign is the reference point. Choices A, B, and D each has a position that is related only to one other object the reference point, which is the stop sign. 5. Choice B is correct. Juan needs to know the distance as well as the direction. Choices A and C are incorrect because the direction and reference point are already known. Choice D is incorrect because the distance is needed.

2 Defining Distance and Speed 8.1.b, page 4 1. Choice A is correct. Distance is a measure of the length of a path between two places. Choice B is incorrect because distance is not a measure of time. Choice C is incorrect because distance is not a measure of direction. Choice D is incorrect because the distance is a measured length, not a unit of length. 2. Choice C is correct. Speed is distance divided by time. Choices A and B are incorrect because it inverts the terms that need to be divided. In addition, choice B is incorrect because dividing by a direction makes no sense since direction is not a numerical value. Choice D is incorrect because dividing by a direction makes no sense since direction is not a numerical value. 3. Choice C is correct because the average speed is the total distance divided by the total time. Choices A and B are incorrect as their numerical values are the total distance and total time respectively, not the total distance divided by the total time. Choice D is incorrect as it is the value for the time divided by the distance, not distance divided by time. 4. Choice D is correct. The total distance is 60 km plus 50 km, or 110 km. Choice A is incorrect as it is the difference between the distances, not the sum. Choices B and C are incorrect as they are the distances for shorter parts of the total trip, not for the total trip. 5. Choice D is correct. Each part of the trip takes one hour, and there are two parts to the trip. Choice B is incorrect as it is the time for only one part of the trip. Choices A and C are incorrect. The time values are not related to the information given. 6. Choice A is correct. The average speed of the car was 60 km/h in the first hour, and 50 km/h in the second hour. Choices B and C are incorrect because the speed decreased, not increased or stayed the same. Choice D is incorrect because there is enough information to answer the question.

3 Solving Problems with Distance, Time, and Average Speed 8.1.c, page 6 1. Choice C is correct. To find the time, you need to divide the distance by the average speed: 80 km/40 km/h = 2 hours. Choice A is the answer you would get if you incorrectly divided the average speed by the distance (S/d). Choice B is incorrect because the time is too short. Choice D is incorrect because the answer can be determined using the method described above. 2. Choice C is correct. To find distance, you need to multiply the average speed by the time: 5.3 m/s x 151 s = 800 m. Choice A is the answer you would get if you incorrectly divided the time by the average speed (t/s). Choice B is incorrect because the distance is too short. Choice D is incorrect because the distance is too long. 3. Choice B is correct. The average speed is the total distance divided by the total time, or 120 miles / 3 hr = 40 miles per hour. Choice A is too high. Choice C and D are too low. 4. Choice D is correct. The distance can be found by multiplying the speed by the time (d = St). Choice A is the answer you would get if you divided the speed by the time. Choice B is the answer you would get if you divided the time by the speed. Choice C is the answer you would get adding the time and the speed together. 5. Choice A is correct. The average speed is the total distance (15 m + 27 m = 42 m) divided by the total time (3 s). So the average speed is 42 m / 3 s = 14 meters per second. Choice B is the answer you would get if you took the average of the individual speeds, which does not take into account the shark went at the higher speed for twice the time. Choice C is what you would get if you divided by 2 seconds instead of 3 seconds. Choice D is what you would get if you added the individual speeds together.

4 Defining Velocity 8.1.d, page 8 1. Choice B is correct. The difference between speed and velocity is that velocity includes direction, as well as a measurement for distance covered over time (i.e. speed). Choice A is incorrect because velocity, not speed, includes direction. Choice C is incorrect because velocity, not speed, is a vector. Choice D is incorrect because although speed and velocity are related, they are not the same thing. 2. Choice B is correct. It includes both the correct speed and direction. Choices A and C do not include any direction. Choice D has the correct direction, but the incorrect speed. 3. Choice C is correct. The size of the velocity is equal to the speed of the object, and does not depend on direction. The speed of the truck is 35 m/s. This is greater than the speed of any of the other choices. Choices A, B, and D are incorrect because their speeds are lower than the speed of the truck. 4. Choice C is correct. The balloon s speed is 4 m / 2 s, or 2 m/s. The direction is upward, so the velocity of the balloon is 2 m/s upward. Choice A is incorrect because it does not include the direction of motion. Choices B and D are incorrect because the speeds are incorrect is the number you would get if you divided the time by the distance instead of the distance by the time. 5. Choice A is correct. The dog and the ball have the same speed and are moving in the same direction. Choices B, C, and D are incorrect because either the speeds of the two objects are not the same, or the directions are not the same, or both. 6. Choice B is correct. Since the monarchs often average between 1 and 2 miles per hour, a speed of 1.5 miles per hour is reasonable; since the butterflies are going from Canada to Mexico, their direction would generally be to the south. Choice A is incorrect because it doesn t include a direction. Choices C and D are incorrect because the speed is too fast for a butterfly. In addition, choice C doesn t include a direction and choice D includes a direction that generally would be incorrect.

5 Changes in Velocity 8.1.e, page Choice D is correct. A change in speed, a change in direction, or a change in both speed and direction each can indicate a change in velocity. Choices A, B, and C are incorrect because each gives an incomplete answer to the question. 2. Choice A is correct. An object moving at a constant velocity does not change speed or direction. A car going 70 km/h per hour down a straight, flat stretch of road fulfills this condition. Choice B is incorrect because turning left indicates a change in direction. Choice C is incorrect because a car going around a curve is constantly changing direction. Choice D is incorrect because a car slowing down is changing speed and pulling off the road is changing direction. 3. Choice A is correct. An airplane going in a circle is constantly changing its direction and hence its velocity. Choice B is incorrect because the airplane would be flying at a constant speed, heading in a constant direction. Choices C and D are incorrect because each of the swimmers described could be swimming at a constant speed in a straight line. 4. Choice B is correct. When the ball bounces, its direction changes. Choice A is incorrect because the size, or speed, is the same before and after the bounce. Choice C is incorrect because the velocity did change during the bounce. Choice D is incorrect because you have information that the direction changed, and a change in direction is a change in velocity. 5. Choice D is correct. This set of vectors shows a change in size of the arrows, indicating a change in speed. Choices A, B, and C are incorrect because within each set of vectors, the arrows are identical in size and the way that they point.

6 Interpreting Graphs of Position and of Speed 8.1.f, page Choice D is correct. The graph shows that after 5 hours, the truck has gone 200 km. Choice A is incorrect because the truck started at 0 km. Choices B shows the distance the truck had gone after 1, 2, and 3 hours. Choice C shows the distance the truck had gone after 4 hours. 2. Choice B is correct. The line is horizontal, so the truck is not moving. Choices A and C are incorrect because the truck is moving up during these time. Choice D is incorrect because there is a time interval when the truck was stopped. 3. Choice C is correct. The average speed is the distance divided by the time. During the first hour, the truck traveled 60 km, so its speed was 60 km / 1 h, or 60 km/h. Choice A is incorrect, because the truck had some speed, not zero speed. Choices B and D are average speeds for different time intervals. B is the average speed from 0 to 3 hours. D is the average speed from 3 to 5 hours. 4. Choice A is correct. The speed steadily increases between 0 and 10 seconds. Choice B is incorrect. The speed does not change during this time interval. Choice C is incorrect because the speed decreases, not increases, during that time interval. Choice D is incorrect because there is a time interval during which the speed increases. 5. Choice D is correct. By looking at the graph, you can see that the dolphin s greatest speed was 10 m/s. Choices A, B, and C are incorrect. A gives the starting speed. B is the value you would find if you calculated the slope of the line between 0 and 10 s. C is the last speed shown on the graph, not the greatest speed.

7 Forces as Vectors 8.2.a, page Choice D is correct. A vector is a quantity that has both size and direction. Choice A is incorrect because in addition to size, direction is also important in measuring a force. Choice B is incorrect because in addition to direction, size is important in measuring a force. Choice C is true of forces, but it doesn t relate to whether force is a vector or not. 2. Choice B is correct. The weight is 490 N in size and acts downward on the ground. Choices A is incorrect because it does not give the direction of the force. Choices C and D gives the incorrect direction for the force. 3. Choice A is correct. The size of the force is the numerical value, which is independent of the direction. Choices B, C, and D are incorrect because each has a greater magnitude than that given for choice A. 4. Choice A is correct. The forces are both 50 netwons, but act in different directions. Choice B is incorrect because the directions are different. Choice C is incorrect because the sizes are the same. Choice D is incorrect because you can compare the size and direction of two forces no matter what is causing the force. 5. Choice C is correct. The force on each side acts in a different direction. Choice A is incorrect because the force would cause the cube to start moving. Choice B is incorrect because it does not take into account the different directions the forces act in. Choice D is incorrect because the force causes the cube to start moving.

8 Adding Forces 8.2.b, page Choice C is correct. The men are pushing in opposite directions. The net force is the difference, 200 N 175 N, or 25 N. The eastward force is larger, so the result is directed eastward. Choices A and B are incorrect because they include the sum of the forces, not the difference. Choice D is incorrect because the direction is incorrect. 2. Choice D is correct. The two athletes are pushing in the same direction. The net force is the sum of the two forces, or 720 N N = 1470 N. Since both forces are to the right, the net result is also to the right. Choices A and B are incorrect because they include the difference of the two forces, not the sum. Choice C is incorrect because it has the size of the forces added rather than subtracted. Choice D is incorrect because the direction of the force is wrong. 3. Choice A is correct. The two forces are equal in size and opposite in direction, so they will cancel each other to produce a zero net force. Choices B, C, and D are incorrect values for the combined forces. Choice C is the sum of the two forces, and Choice D is the ratio of the two forces. 4. Choice B is correct. The rocket is being pushed upward and its weight is pulling the rocket downward. The net force is the difference, 15 N 4 N = 12 N. The direction is the direction of the greater force; upward. Choice A is incorrect because it is too small; it is equal and opposite the direction of the rocket s weight. Choice C is incorrect because it is in the wrong direction and too large; it is equal and opposite the force propelling the rocket upward. Choice D is incorrect because it is in the wrong direction and too large; it is the result of incorrectly adding the forces, not taking into account that they are acting in opposite directions. 5. Choice A is correct. Because the forces are acting in opposite directions, the size of the net force is the difference between the two forces. 80 N 60 N = 20 N. Choices B and C are the values for the two individual forces, not the net force. Choice D is the result if both forces act in the same direction instead of in opposite directions.

9 Balanced Forces 8.2.c, page Choice D is correct. By definition, forces are balanced when the effect is the same as no force. Choice A is incorrect because forces with the same size and direction cannot balance each other. Choices B and C are incorrect because the combined forces include all the forces on the object there is no separate balanced force that other forces are compared to. 2. Choice D is correct. The velocity changes as the box slides. The motion of the box is changing, so the forces are not balanced. Choices A and B are incorrect because they suggest the forces are balanced, which is not the case. Choice C is incorrect because forces are acting on the box as it slides. 3. Choice A is correct. Since the biker is going at a constant speed and is not turning, balanced forces are acting on the biker and the bicycle. Choice B is incorrect because the direction of the force is opposite that of the force that balances the force the biker exerts. Choice C is incorrect because both the size and the direction of the force do not balance the force exerted by the biker. Choice D is incorrect because other forces must be acting on the bike or the forces could not be balanced. 4. Choice B is correct. Since the book is at rest, the force of the table pushing up on the book (5N) is equal and opposite the force of gravity pulling down on the book. This force is the book s weight. Choice A is too small. Choice C and D are too large. 5. Choice D is correct. Since the rock is at rest, the forces on the rock are balanced. The rock s weight is the downward force on the rock; the contact forces of friction and compression provide the upward push against the rock s weight. Choice A is incorrect because forces are acting on the rock. Choice B is incorrect because the rock is fairly heavy, and given enough force, even a light rock will slide. Choice C is incorrect because the force of gravity would pull the rock downward if it were not balanced by other forces.

10 Identifying Forces on an Object at Rest 8.2.d, page Choice B is correct. A static object is not moving. It remains at rest because the forces acting on it are balanced. Choices A, C, and D are incorrect because, although each describes how a specific force acts on the ball, none explains why a static object remains at rest. 2. Choice C is correct. Since the plate is not moving, balanced forces must be acting on it. Gravity pushes down on the plate and elastic forces from the table push up on the plate. Choices A and B are incorrect. The plate is not sliding or being pushed, so friction is not one of the forces acting on it. Choice D is incorrect, because the plate is not being stretched, so it is not under tension. 3. Choice C is correct. Since you are pushing on the chair, but the chair doesn t move, the force of friction opposes the force you are applying as you push. Choice A and D are incorrect because these forces are what keep the chair resting on the floor, neither moving up nor down. Choice B is incorrect because this is the type of force that you apply to the chair when you push it. 4. Choice A is correct. Tension balances the downward pull of gravity. Choice A is incorrect because the forces will stretch the wires and picture, not compress them. Choices C and D are incorrect because gravity and weight are the same force in this case, and it acts to pull the picture downward, not upward. 5. Choice D is correct. The table compresses and exerts an elastic force back on your hand. Choice A is incorrect, because the forces on the table are balanced and the table is not moving compared to your hand. Choice B is incorrect. You are not sliding or trying to slide your hand across the table, so there is no friction. Choice C is incorrect because you are compressing the table, not stretching it, so there is no tension. 6. Choice A is correct. Two balanced forces keep the balloon from rising. Choice B is incorrect because these forces apply to the chair or string rather than to the balloon. Choice C is incorrect because compression and friction are not forces acting on the balloon. Choice D is incorrect because tension in the string would pull the balloon downward, not up, and gravity is only one of the downward forces on the balloon.

11 Unbalanced Forces and Changes in Velocity 8.2.e, page Choice A is correct. Since the person kicks the ball in the same direction as the ball is moving, the force applied is in the direction of motion of the ball. The ball will speed up. Choices B and D are incorrect because the force is not applied in the direction opposite the ball s motion or perpendicular to the ball s motion, but in the same direction as the ball s motion. Choice C is incorrect because an unbalanced force is applied. 2. Choice B is correct. A push in the same direction in which the wagon is moving will cause the wagon to speed up. Choice A is incorrect because there is a change in motion. Choice C is incorrect because a push in the other direction will slow the wagon down. Choice D is incorrect because a force at a right angle will turn the wagon, not change its speed. 3. Choice B is correct. Because the bicycle is turning, there must be an unbalanced force on it to cause it to change direction. Choices A and C are incorrect, because neither choice would result in a change in motion. Choice D is incorrect, because you know the motion is changing, which implies an unbalanced force. 4. Choice D is correct. The ball slows down and stops. This implies a force was applied in the opposite direction of the ball s motion. Choice A is incorrect because the ball changes its motion. Choice B is incorrect because such a force would cause the ball to change direction by moving upward rather than to stop. Choice C is incorrect because such a force would cause the ball to continue moving in the same direction at a greater speed than before. 5. Choice A is correct. For an object to change its motion, an unbalanced force must act on it. To slow the object down, the force must act opposite the motion. Choice B is incorrect as the force described would cause the object to move faster, not slower. Choices C and D are incorrect as no forces or balanced forces would not change the motion of the object. In addition, two forces that cancel each other would not cancel out an object s motion.

12 Force, Mass, and Acceleration 8.2.f, page Choice D is correct. Increasing the force exerted on an object increases the acceleration the object experiences. Choices A and B are incorrect because mass is a property of the object and is not determined by the force acting on it. Choice C is incorrect because it is the opposite of what will happen if the force on an object is increased. 2. Choice C is correct. For any given force, an object with a lower mass will have a greater acceleration than an object with a higher mass. Choices A and B are incorrect because the force does not determine the mass. Choice D is incorrect because it is the opposite of what will happen when a force of the same magnitude is applied to objects of different masses. 3. Choice B is correct. The objects are accelerating at the same rate they are moving together. The car needs a larger force than the bicycle to have the same acceleration because it is more massive. Choice A is incorrect because the bicycle needs less force than the car. Choices C and D are incorrect because there are forces (the car and bicycle are both turning), and the forces are not the same size. 4. Choice D is correct. This ball has the lowest mass. Therefore, if you apply the same force to all four of the balls, this ball will have the greatest acceleration when it is being hit. Choice B is incorrect because the softball would experience the least acceleration. Choice A is incorrect because the baseball would experience a similar acceleration to the softball. Choice C is incorrect because the tennis ball would experience about half the acceleration of the plastic ball. 5. Choice A is correct. A larger force will cause a greater acceleration. Choices B, C, and D are incorrect. The acceleration will not decrease, stay the same, or become zero.

13 Gravitational Forces in Space 8.2.g, page Choice A is correct. Gravity is the force of attraction that objects exert on one another because the objects have mass. Choice B is incorrect because gravity is an attractive force. Choices C and D are incorrect because gravity does not cause objects to change in mass, although it may cause the density of dust clouds in space to increase, leading to the formation of stars. 2. Choice B is correct. Gravity causes the dust and gas particles in a cloud in space to be attracted to one anther, causing the matter to become very dense and eventually form a star. Choice A is incorrect because gravity does not cause dust to form in space; for a star to form, the dust must already be there. Choice C is incorrect because gravity does not cause space to form nor is this a step in the formation of stars. Choice D is incorrect because gravity does not cause the stellar wind to blow, nor is this a step in the formation of stars. 3. Choice B is correct. Just as gravity causes a star as it is forming to be densest at its center, so matter in a galaxy also tends to collapse toward the center, causing a higher density of stars in this region. Choice A is incorrect because this would be the least dense region of a galaxy. Choices C and D are incorrect because these parts of the galaxy would be less dense than the center. 4. Choice C is correct. As Earth formed, gravity caused the dust and gas to collapse in such a way that any parts that bulged out of a spherical shape were pulled back into a spherical shape. Choices A, B, and D are incorrect because they do not explain why Earth is a sphere. 5. Choice A is correct. The Moon orbits Earth because of Earth s gravitational pull on it. Choice A is incorrect, because the Moon s pull on Earth affects Earth, not the Moon itself. Choice C and D describe the forces between the Moon and the Sun, or Earth and the Sun, not the Moon and Earth. 6. Choice D is correct. Gravity is the force that causes objects in space to move in orbits. If the masses are similar, the objects orbit each other. Choices A, B, and C do not explain why the stars would have any kind of orbit.

14 The Structure of the Atom 8.3.a, page Choice A is correct. Matter is made up of atoms. This is a very important principle of science. Choice B is incorrect because energy is a property of matter, not a unit of matter, C and D are incorrect because protons and electrons are not made of atoms, rather, atoms are made of protons and electrons (and neutrons). 2. Choice C is correct. The two subatomic particles that form the nucleii of atoms are protons and neutrons. Choices A, B, and C are incorrect because electrons are located in the electron cloud around the nucleus. 3. Choice B is correct. Electrons move about the nucleus in an electron cloud. Choice A is incorrect because atoms do not move around the nucleus, they are composed of a nucleus and the particles moving about the nucleus. Choices B and D are incorrect because neutrons and protons form the nucleus. 4. Choice B is correct. Electrons have 1/2000 the mass of neutrons and 1/2000 of the mass of protons. Choice A is incorrect because atoms have higher mass than any of the subatomic particles because they are composed of subatomic particles. Choices C and D are incorrect because protons and neutrons each are 2000 times more massive than electrons. 5. Choice D is correct. Protons have a positive charge. Choice A is incorrect because atoms are generally neutral. An atom that has lost an electron is a positively charged ion, but atoms do not always become positive ions. Choice B is incorrect because electrons have a negative charge. Choice C is incorrect because neutrons have no charge. 6. Choice A is correct. The nucleus is an extremely small part of the atom. Choice B is incorrect because the nucleus is much smaller than half the size of the electron cloud. Choices C and D are incorrect, as they are all larger than choice B, which is already too large.

15 Elements and Compounds 8.3.b, page Choice B is correct. Elements are defined as being made up of only one type of atom; compounds are defined as being made of two or more types of atoms. Choice A is incorrect because the definitions of element and compound are switched. Choices C and D are incorrect because compounds can form through either ionic or covalent bonding. 2. Choice D is correct. Elements generally do not retain their properties when they combine to form compounds. Choices A, B, and C are incorrect because neither sodium nor chlorine retains its original properties in forming sodium chloride. 3. Choice C is correct. Water is made up of hydrogen and oxygen, both of which are gases at the temperatures at which water is a liquid. Choice A is incorrect because water is not formed from chlorine. Choice B is incorrect because water is not formed from either sodium or chlorine (sodium chloride, or salt, is). Choice D is incorrect because water does not form from sodium. 4. Choice A is correct. Ionic bonds involve the transfer of electrons; covalent bonds involve the sharing of electrons. Choice B is incorrect because it switches the definitions of ionic and covalent bonding. Choices C and D are both incorrect because elements in neither ionic nor covalent compounds generally retain their individual properties once they have combined. 5. Choice D is correct. A compound has properties that are different from its constituent elements. Choices A and B are incorrect because a compound will not have the same properties as any individual element. Choice C is incorrect because the compound takes on its own properties, not the combination of the properties of the individual elements.

16 Atomic and Molecular Structures of Solids 8.3.c, page Choice C is correct. Ions in ionic compounds often have equal and opposite charges, so they attract each other with equal force, causing a regular spacing of ions, characteristic of a crystal structure. Choice A is the opposite of what happens since the metal and nonmetal ions are attracted to one another. Choice B is incorrect because all particles in an ionic bond are ions and thus charged particles. Choice D is incorrect because ionic bonds do not change into covalent bonds. 2. Choice C is correct. Polymers are molecules that have repeating units. Choice A is incorrect because polymers are not very simple. Choice B is incorrect because, although many polymers contain carbon, not all molecules containing carbon are polymers. Choice D is incorrect because polymers do not necessarily have a crystalline shape. 3. Choice B is correct. The ionic compound, NaCl is a crystal solid. Choices A and B are incorrect because NaCl is not a polymer or ring molecule. Choice D is incorrect because the shape of solid sodium does not determine the structure of NaCl. 4. Choice D is correct. This molecule has a branched chain structure. Choice A is incorrect because it is a simply a chemical formula for a simple molecule. Choice B is incorrect because this molecule has a ring structure. Choice C is incorrect because this molecule has a straight chain structure. 5. Choice B is correct. It shows a ring structure. Choice A is incorrect, as it shows a simple bond. Choices C and D are incorrect, as they show straight and branched chains respectively.

17 Matter and Molecular Motion 8.3.d, page Choice B is correct. Matter that can take on the shape of its container does not have a fixed shape. The question indicates that the matter does have a fixed volume. As the chart indicates matter having a fixed volume without having a fixed shape is liquid. Choice A is incorrect because matter in its solid state has both a fixed volume and a fixed shape. Choice C is incorrect because matter in its gaseous has neither a fixed volume nor a fixed shape. Choice D is incorrect because vapor is another name of a gas. 2. Choice A is correct. As the chart indicates, matter in its solid state has both a fixed volume and a fixed shape. Choice B is incorrect because matter in its liquid state has a fixed volume without having a fixed shape. Choice C is incorrect because matter in its gaseous has neither a fixed volume nor a fixed shape. Choice D is incorrect because a solid substance has both a fixed volume and a fixed shape. 3. Choice C is correct. As the chart indicates, matter in its gaseous state has neither a fixed volume nor a fixed shape. Choice A is incorrect because matter in its solid state has both a fixed volume and a fixed shape. Choice B is incorrect because matter in its liquid state has a fixed volume without having a fixed shape. Choice D is incorrect because a gaseous substance has neither a fixed volume nor a fixed shape. 4. Choice D is correct. Particles of matter, no matter the type of particle, are always in motion. Choice A is incorrect because molecules are in motion, as well as ions atoms. Choice B is incorrect because atoms are in motion as well as ions and molecules. Choice C is incorrect because ions are in motion as well as atoms and molecules. 5. Choice D is correct. Temperature is a measure of the kinetic energy of the particles in a substance. Choices A and B are incorrect because temperature depends not on whether the substance has a fixed shape or a fixed volume but on the kinetic energy of the particles; for any given substance, however, the kinetic energy of the particles determines whether the substance has a fixed volume or a fixed shape, both, or neither. Choice C is incorrect because it is the converse of what is true; the state of matter of a substance depends on the kinetic energy of the particles. 6. Choice C is correct. Particles in a gas move faster on average than particles in the liquid or solid form of the same substance. Choices A and B are incorrect because a substance in its solid or liquid state have particles with slower average speeds. Choice D is incorrect because for any single substance the state of matter gives a relative indication of the average speed of the particles.

18 Contrasting Solids, Liquids, and Gases 8.3.e, page Choice D is correct. This helps explain why a gas has neither a fixed shape nor a fixed volume. Choice A is not true of gases nor of any other state of matter; particles in each state of matter move. Choice B is incorrect because it describes how particles in a solid move. Choice C is incorrect because it describes how particles move in a liquid. 2. Choice B is correct. This helps explain why a solid has a fixed shape and a fixed volume. Choice A is not true of solids nor of any other state of matter; particles in each state of matter move. Choice C is incorrect because it describes how particles move in a liquid. Choice D is incorrect because it describes how particles in a gas move. 3. Choice C is correct. This helps explain why a liquid has a fixed volume but not a fixed shape. Choice A is not true of liquids nor of any other state of matter; particles in each state of matter move. Choice B is incorrect because it describes how particles move in a solid. Choice D is incorrect because it describes how particles in a gas move. 4. Choice A is correct. There is the least space between particles of a solid and the most space between particles in a gas. Choice B is incorrect because there is more space between particles in a gas than in a liquid. Choice D is incorrect because it gives the order from the most space between the particles to the least space between the particles. Choice C is incorrect because there is more space between particles of a liquid than a solid and more space between particles of a gas than a liquid. 5. Choice C is correct. Liquids flow because the particles slide past each other. Choice A is incorrect because liquid particles are not locked in place and cannot pass through one another. Choice B is incorrect, as it describes how particles in a gas move. Choice D is incorrect because liquids are made up of particles. 6. Choice A is correct. A gas expands to fill the space it is in. Choice B is incorrect; a gas expands if the pressure drops. Choice C is incorrect because it is the opposite of what is true. Choice D is incorrect because the particles have a decrease in average kinetic energy when there are fewer of them in the same space and thus, the temperature goes down, not up.

19 Using the Periodic Table to Learn about Elements 8.3.f, page Choice D is correct. The chemical symbol is given in the middle of the square for the element, above the name of the element. None of the other choices are the chemical symbol for manganese, nor are they symbols for any of the other elements. 2. Choice C is correct. The name of the element is given below the chemical symbol. Choice A is incorrect because freon is not an element. The elements named in Choices B and D have the symbol Fm and P respectively. 3. Choice A is correct. The atomic number of an element is given above the chemical symbol. Choice B is incorrect because it is the atomic mass of manganese. Choices C and D are incorrect because they are the atomic number and the atomic mass of iron. 4. Choice D is correct. The atomic mass is found under the element s symbol. Choice A is incorrect because it is mercury s atomic mass. Choice B is incorrect because it is the atomic mass for molybdenum. Choice C is incorrect because this is the atomic number for meitnerium. 5. Choice D is correct. Ca is the symbol for calcium and O is the symbol for oxygen. Choices A, B, and C are incorrect. The symbol for carbon is C, not Ca, and the symbol for osmium is Os, not O. 6. Choice B is correct. There are three elements in this chemical formula: nitrogen, hydrogen, and chlorine. Chemical symbols are either a capital letter alone or a capital letter and a lowercase letter. Choice A is too low a number, since three chemical symbols are included. Choice C is incorrect because it is too high a number; a lowercase letter on its own cannot be a chemical symbol. Choice D is incorrect because it is the number of atoms, not the number of elements in the molecule represented by this chemical formula.

20 Galaxies 8.4.a, page Choice D is correct. A galaxy is defined as a large group of stars held together by gravity; most galaxies have at least some gas interspersed with the stars, as well. Choice A is incorrect because it describes a solar system, not a galaxy. Choice B is incorrect because comets traveling around a star are part of a solar system. Choice C is incorrect because stars traveling away from one another does not define a galaxy. 2. Choice B is correct. An elliptical galaxy has very little interstellar gases and dust, the materials from which new stars form. Therefore, most of the stars in an elliptical galaxy are old. Choice A is incorrect because it is the opposite of what is true. Choice C is incorrect because elliptical galaxies have very little interstellar dust. Choice D is incorrect because most of the stars in an elliptical galaxy are found near the center of the galaxy, where the stars are most densely packed. 3. Choice A is correct. An irregular galaxy does not have a regular shape, so its shape is not easy to describe. Choice B is incorrect because the stars themselves do not have an irregular shape. Choice C is incorrect because irregular galaxies contain stars. Choice D is incorrect because galaxies are held together by gravity. 4. Choice C is correct. In a spiral galaxy, most of the older stars are found near the center of the galaxy. Choice A is incorrect because there are few stars around the edges of the galaxy. Choice B is incorrect because most of the older stars are in the bulge, and the arms contain many young stars. Choice D is incorrect because a spiral galaxy does have older stars. 5. Choice C is correct. Our galaxy, the Milky Way, is a very large spiral galaxy. Choice A is incorrect because our galaxy is spiral, not elliptical. Choice B is incorrect because our galaxy is neither small nor irregular. Choice D is incorrect because the type of galaxy we live in known. 6. Choice A is correct. The spherical shape and old stars suggest the galaxy is an elliptical one. Choices B and C are incorrect because irregular and spiral galaxies are not spherical. Choice D is incorrect because the spiral that is merging would contain new stars, and the combination would not look spherical while they were merging.

21 The Sun and Other Stars 8.4.b, page Choice D is correct. The Sun is located a little more than half way between the center and edge in an arm of our galaxy. Choice A is incorrect because the Sun is not in the center of the galaxy. Choice B is incorrect because the Sun is not at the edge of the galaxy. Choice C is incorrect because the Sun is not in the bulge, which is at the center of the galaxy. 2. Choice C is correct. The color of a star is determined by its temperature. Choice A is incorrect because a star s temperature does not correlate with its size. Choice B is incorrect because a star s temperature does not determine where it is likely to be located in the galaxy. Choice D is incorrect because a star s temperature does not determine its age. 3. Choice A is correct. Red and orange stars are cooler than other stars. Choice B is incorrect because stars that are hot tend to be blue or white. Choices C and D are incorrect because a star s color does not indicate anything about its distance from Earth. 4. Choice D is correct. The bottom chart gives examples of different stars being different sizes. Choices A and C are incorrect because Arcturus and Capella are examples of giant stars. Choice B is incorrect because Betelgeuse is an example of a supergiant star. 5. Choice B is correct. The top chart indicates that a star that is 25,000 C is blue-white in color. Choice A is incorrect because an orange star has a temperature of 3000 to 5000 C. Choice C is incorrect because a yellow star has a temperature of 5000 to 6000 C; the mass does not relate to the temperature. Choice D is incorrect because a red star has temperature of below 3500 C. 6. Choice C is correct. The bottom chart indicates that Sirius B is a white dwarf. The bottom chart indicates that white stars are between 7500 C and 10,000 C. Choice A is incorrect because red stars tend to fall in this temperature range, but Sirius B is a white star. Choice B is incorrect because yellow and orange stars tend to fall in this temperature range, but Sirius B is a white star. Choice D is incorrect because blue-white stars tend to fall into this temperature range, but Sirius is a white star.

22 Distances in Space 8.4.c, page Choice C is correct. Using kilometers or miles to measure distances in the solar system gives quantities in the millions or billions. Such numbers are difficult to work with. Choice A is incorrect because how long it takes to make these measurements is not influenced by the units used. Choice B is incorrect because the measurements can be made accurately no matter what units are used. Choice D is incorrect because making measurements of the solar system in kilometers does not yield small fractions. 2. Choice B is correct. An astronomical unit (AU) is defined as the average distance between Earth and the Sun, about 150 million kilometers. Choice A is not the correct definition and the distance is smaller than an astronomical unit. Choices C and D are not the correct definition and are each larger than an astronomical unit. 3. Choice C is correct. A light-year is the distance light travels in one year. Choices A and B are both incorrect because a light-year is a unit of distance, not of time. Choice D is not the correct definition and it is impossible to determine the distance around one orbit with without more information. 4. Choice A is correct. Astronomical units are the units usually used for objects in the solar system. Choices B, C, and D are not the best answer. Light-years are more useful outside the solar system, as distances inside the solar system are small fractions of a light year. Kilometers and meters are more useful for smaller distances such as distances measured on Earth. 5. Choice C is correct. Earth is 1 AU from the Sun and that Saturn is 9.5 AU from the Sun, or about ten times as far from the Sun as Earth is. Choices A and B are incorrect because they are too small. Choice B is how much farther Jupiter is from the Sun. Choice D is incorrect because it is too large; it is how much farther Neptune is from the Sun. 6. Choice B is correct. The diagram gives units in astronomical units. It shows that the asteroid belt is almost 4 AU from the Sun. Choice A is incorrect because it is too small; Mars is between 1 and 2 AU from the Sun. Choices C and D are incorrect because the diagram doesn t give distances in light-years and these distances are much too large.

23 Light in Space 8.4.d, page Choice D is correct. Stars produce light by nuclear fusion. Choice A is incorrect because this explains why other objects in the solar system give off light. Choice B is incorrect because refraction is the bending of light, not a way to produce it. Choice C is incorrect because this involves the splitting of atomic nucleii and is not the process stars use to produce light. 2. Choice C is correct. Hydrogen nucleii collide often and with great force because of the high density and heat of the gas at the center of a star to form helium nucleii. Choices A, B, and C are incorrect because they do not explain why hydrogen fuses into helium inside stars. 3. Choice A is correct. Stars produce and give off visible light, while other objects such as planets and moons are visible because of reflected light. Polaris is the only star in the list. Choice B is incorrect because Neptune is a planet; it shines because it reflects light from the Sun. Choice C is incorrect because the Moon is a planetary satellite; it shines because it reflects light from the Sun. Choice D is incorrect because comets, like planets and planetary satellites shine because they reflect light from the Sun. 4. Choice D is correct. Planetary moons, including those of Jupiter, shine by light reflected by the Sun. Choice A is incorrect because planetary moons do not give off their own light. Choice B is incorrect because Jupiter does not produce visible light; like its moons, Jupiter reflects the Sun s light. Choice C is incorrect because Jupiter s moons mostly reflect light from the Sun, not light from Earth. 5. Choice B is correct. A galaxy is a collection of millions or billions of stars. These stars produce and give off light, which is why we can see them. Choice A is incorrect because dust does not produce light. Choices C and D are incorrect because galaxy do not shine by reflected light, but instead produce their own light.

24 The Solar System 8.4.e, page Choice A is correct. Earth is the closest of the planets listed; it is the third planet from the Sun. Choice B is incorrect; Mars is the fourth planet from the Sun. Choice C is incorrect; Neptune is the eighth planet from the Sun. Choice D is incorrect; Pluto is the ninth planet from the Sun. 2. Choice D is correct; Saturn is a gas giant. Choices A, B, and C are incorrect; Venus, Mercury, and Mars each have a rocky crust. 3. Choice B is correct; Pluto is the only outer planet to have a rocky crust. Choices A, C, and D are incorrect; Jupiter, Uranus, and Neptune are all gas giants. 4. Choice B is correct. Jupiter has a diameter more than 11 times that of Earth; it is the largest planet. Choice A is incorrect because Earth is smaller than Jupiter; it is the fifth largest planet. Choice C is incorrect because Neptune has a diameter 3.88 times that of Earth; it is the fourth largest planet. Choice D is incorrect because Uranus has a diameter 4.01 times that of Earth; it is the third largest planet. 5. Choice C is correct. Pluto has a diameter under 0.2 times that of Earth; it is the smallest planet. Choice A is incorrect because Mars has a diameter about half that of Earth; it is the seventh largest planet. Choice B is incorrect because Mercury has a diameter more than 0.3 times that of Earth; it is the eighth largest planet. Choice D is incorrect because Venus has a diameter just smaller than that of Earth; it is the sixth largest planet. 6. Choice A is correct. Jupiter has a period of rotation of 9.93 hours. It is the planet that is spinning the fastest. Choice B is incorrect because it has a period of rotation of 24.6 hours; Jupiter is spinning more than twice as fast as Mars. Choice C is incorrect because Neptune has a period of rotation of 16.1 hours; Jupiter is spinning almost twice as fast as Neptune. Choice D is incorrect because Pluto has a period of rotation of 6.39 Earth days; Jupiter is spinning more than 15 times faster than Pluto.

25 Chemical Reactions: Reactants and Products 8.5.a, page Choice D is correct. A chemical reaction involves a formation of new substances through the breaking of chemical bonds, the forming of chemical bonds, or both. Choice A is incorrect because a chemical reaction is the subject of a chemical equation, not a way of writing a chemical equation. Choice B is incorrect because using chemical symbols is a way to indicate which chemicals are involved in a chemical equation. Choice C is incorrect because it describes a change of state, which is not a physical change, not a chemical change. 2. Choice C is correct. This the only choice in which elements combine, forming a new substance. Choices A, B and D are incorrect because they describe physical changes that do not involve the formation of new chemical substances. 3. Choice B is correct. In a chemical reaction, the reactants and products often have different physical as well as chemical properties; therefore the state or states of matter of the reactants are often different than the state or states of matter of the products. Choice A is incorrect because the states of matter of the products and reactants often differ from each other. Choice C is incorrect because the temperature of the reactants determine their own state, not the state of the product. Choice D is incorrect because, although it is true, it doesn t address the question asked. 4. Choice C is correct. The reactants are on the left side (the base) of the arrow. Choices A and B are incorrect because each includes only one of the two reactants. Choice D is incorrect because it is the product, not a reactant. 5. Choice D is correct. The product or products are on the right side (the point) of the arrow. Choices A, B, and C are all give reactants, not products. 6. Choice A is correct. There are two molecules shown on the right side of the arrow. These are the two products. Choice B is incorrect because this is the total number of products and reactants. Choice C is incorrect because this is the number of each type of molecule in this reaction. Choice D is incorrect because this is the total number of molecules that are reactants; it is also the total number of molecules that are products.

26 Chemical Reactions: Conservation of Matter 8.5.b, page Choice A is correct. The law of conservation of matter states that in a chemical reaction, atoms are neither created nor destroyed. Therefore, in any chemical reaction, all of the atoms of each element present in the reactants are also present in the products. Choice B is incorrect because the number of molecules in the reactants can differ from the number of molecules in the products, as chemical bonds break or form or both during the chemical reaction. Choices C and D are incorrect because neither the sum of the coefficients nor the sum of the subscripts necessarily correlates with the number of atoms present on each side of the equation. 2. Choice B is correct. In every chemical reaction total mass of the reactants is always equal to the total mass of the products. 80 g of one substance combined to 40 g of another substance is equal to 120 g. Choices A, C, and D are incorrect because in a chemical reaction mass cannot be created or destroyed. 3. Choice C is correct. A balanced equation has the same number of atoms of each element on both sides of the equation. The atoms are only arranged differently. Choices A and B are incorrect because the masses of all elements are the same before and after a chemical reaction. Choice D is incorrect because the atoms are not arranged in the same way on each side of the equation. 4. Choice C is correct. The total mass before the reaction is equal to the total mass after the reaction. Choices A, B, and D are incorrect because the numbers of atoms of each element must be the same.