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Physical Physics The Study of How Matter Behaves Physics is the branch of science that concerns the behavior of matter in our world—the forces that cause matter to behave as it does. Physics helps to explain how cellular molecules can move from a lower concentration in an organism to a higher one, how ocean tides occur, and how matter exists in the states of a solid, liquid, or gas. (page 555) Physical Science Physics The Study of How Matter Behaves Many of the properties and behaviors of matter can be explained by force and energy. A force shows the presence of energy in an environment. Energy is the capacity to do work. The area of physics that deals with forces, energy, and their effect on bodies is mechanics. (page 555) Physical Science Physics The Study of How Matter Behaves Physical Science Physics Mechanics The study of mechanics was one of the first sciences developed. Ancient Greek philosopher and scientist Aristotle theorized that heavy bodies fall faster than light bodies. This theory was proved false in the early 17th century by Italian scientist and mathematician Galileo, who dropped items of different weights from the leaning tower of Pisa. (page 556) Physical Science Physics Mechanics Physical Science Physics Mechanics The force acting upon the objects was not fully understood, however, until Englishman Sir Isaac Newton formulated laws of gravity and motion that explained how different forces act on objects. (page 556) Physical Science Physics Mechanics Physical Science Physics Mechanics Physical Science Physics The Force of Gravity Gravity is the most commonly experienced of all forces in nature. The presence of gravity was first proposed by Newton when he observed the motion of an apple falling from a tree. On the basis of this simple observation, he developed the Law of Universal Gravitation, which holds that every body having a mass exerts an attractive force on every other body having a mass in the universe. (page 556) Physical Science Physics The Force of Gravity The strength of the force depends on the masses of the objects and the distance between them. (Mass is the measure of the amount of matter in an object.) Thus, the apple's falling illustrates the gravitational pull (attraction) of the larger Earth on the smaller apple. The Law of Universal Gravitation also explains how the planets, attracted by the much larger Sun, remain in their orbits as they revolve around it. (page 556) Physical Science Physics NEWTON'S THREE LAWS OF MOTION The Law of Inertia A body remains at rest or continues in a state of uniform motion unless a force acts on it. For example, when you drive a car and suddenly jam on the brakes, you continue to move forward. This is because your body's tendency is to remain in the same state of uniform motion (moving forward). The brakes were applied to the car, so its uniform motion was changed. (page 556) Physical Science Physics NEWTON'S THREE LAWS OF MOTION The Law of Applied Force A body's change in speed and direction is proportional to the amount of force applied to it. For example, the vanes on a windmill, which move by the force of the wind, will accelerate according to the speed and direction of the wind that drives them. (page 556) Physical Science Physics NEWTON'S THREE LAWS OF MOTION The Law of Action and Reaction For every action there is an equal but opposite reaction force. For example, a gun's muzzle kicks backward when a bullet is discharged from it. (page 556) Physical Science EXERCISE 1 Laws of Force and Motion (page 557) Directions: Identify the following statements as (G) illustrating Newton's Law of Universal Gravitation, (I) applying to the Law of Inertia, (AF) applying to the Law of Applied Force, or (AR) applying to the Law of Action and Reaction. 1. ____ A ball on a pool table rebounds off another ball it just hit. 2. ____ A rocket is propelled upward by the powerful downward discharge of exhaust gases. 3. ____ A bullet fired into the air eventually falls to the ground. 4. ____ A pendulum in a clock, once set in motion, continues to swing, thereby regulating the clock's movement. 5. ____ A jet airplane, upon landing, lowers the flaps on its wings. The flaps create drag, a force that reduces lift and helps the plane to slow down. Physical Science EXERCISE 2 (page 557) The Force of Gravity Directions: Read the paragraph below and answer the questions that follow. An astronaut weighs in before blast-off. He weighs only a fraction of his original weight when he steps on a scale on the moon. Journeying to Jupiter, he finds that his weight has increased several times over his original weight. 1. How may these changes in weight be best explained? (1) the amount of force each planetary body exerts as the astronaut weighs himself (2) the distance from the Sun of the planetary bodies on which he weighs himself (3) changes in the atmospheric pressure on the different heavenly bodies (4) the amount of calories consumed during the flight (5) the duration of time that elapsed between weigh-ins 2. What do you estimate the weight change for the same astronaut would be if he were to land on Mercury? Physical Science Work, Energy, and Power According to physics, work occurs when a force succeeds in moving an object it acts upon. For example, a person who lifts a 50-pound weight one foot off the floor is performing work. For work to be performed, the movement of the object must be in the same direction as the force—in this case vertical. (page 558) Physical Science Work, Energy, and Power (page 558) Work may be expressed as any force unit times any distance unit and may be written as follows: W = FxD The amount of work done is the amount of force multiplied by the distance moved. In the preceding example, 50 foot-pounds of work is done when 50 pounds are lifted one foot: 50 lb x 1 ft = 50 ft lb Physical Science Work, Energy, and Power Energy is required to do work. In the example above, muscular energy is illustrated in the form of a body that is capable of doing work. Energy may be classified as either kinetic or potential energy. (page 558) Physical Science Work, Energy, and Power Kinetic energy is energy possessed by a body in motion. The form of energy shown by a moving train is kinetic energy. (page 558) Physical Science Work, Energy, and Power Potential energy is energy that is stored or is available for use by a body. For example, coal has potential energy that is released only when it is burned. A boulder positioned on a hilltop has potential energy before it is released. When the boulder is pushed, its potential energy becomes kinetic. (page 558) Physical Science Work, Energy, and Power Power is the rate at which work is done. Power is generally measured in horsepower, which is equal to 550 footpounds per second or 33,000 footpounds per minute. (page 558) Physical Science The Law of Conservation of Energy The Law of Conservation of Energy holds that all of the energy of the universe is conserved. The capacity for energy to do work can be changed from one kind to another, but it cannot be lost. This principle can be illustrated in the following example of energy generated from a waterfall. (page 558) Physical Science The Law of Conservation of Energy Water possesses potential energy. When water moves rapidly in a downward motion, drawn by the pull of gravity, the potential energy is changed into kinetic energy. Kinetic energy from a waterfall can be harnessed to power a turbine, a rotary engine, creating rotational energy. This is sufficient to generate electrical energy, which in turn is converted into light and heat energy, which we use in our homes. The initial potential energy has been changed into five different forms. (page 558) Physical Science EXERCISE 3 Forms of Energy (page 559) Directions: Identify the following statements as either demonstrating kinetic energy (K) or demonstrating potential energy (P). 1. ____ a strong west wind blowing across a region 2. ____ a stick of unlit dynamite 3. ____ a hamburger 4. ____ a waterfall Physical Science EXERCISE 4 Types of Energy (page 559) Directions: Read the following definitions of the five types of energy. Then choose the best answers for the questions below. nuclear energy - energy from splitting an atom or fusing atoms chemical energy - energy from the reaction of two or more substances combining with one another electrical energy-energy from an electric current solar energy - energy from the heat of the Sun steam energy - energy from steam pressure Physical Science EXERCISE 4 Types of Energy (page 559) 1. Which form of energy results from the fission of uranium-235 nuclei that is used to generate electrical power? (1) nuclear energy (2) chemical energy (3) electrical energy (4) solar energy (5) steam energy Physical Science EXERCISE 4 Types of Energy (page 559) 2. Which form of energy results from the ignition of a gas and air mixture and powers a car? (1) nuclear energy (2) chemical energy (3) electrical energy (4) solar energy (5) steam energy Physical Science Simple Machines A machine is a device that transmits or multiplies force. A machine operates on the principle of a little force as being applied through a great distance and a great resistance being overcome through a short distance. (page 560) Physical Science Simple Machines The lever Physical Science Simple Machines The lever Physical Science Simple Machines A lever is a simple machine used to perform work by lifting a great weight. A lever is just a bar that is free to pivot on its support (called a fulcrum). Through the use of a lever, for example, a 1,000-pound weight can be lifted with relatively little effort (force). (page 560) Physical Science Simple Machines (page 560) The illustration above shows that it would take 100 pounds of force for a person to lift a 1,000-pound weight positioned 1 foot from the fulcrum when the lever bar is 10 feet long. This may be expressed as follows: 1,000 lbx1 ft = 100lbx10ft Physical Science Simple Machines In this case a relatively small force (100 lb) applied at a great distance from the object (10 ft) is able to overcome great resistance (1,000 lb). According to this principle the greater the distance between the fulcrum and the applied force, the less force required to perform the work. (page 560) Physical Science Simple Machines The wheelbarrow, the crowbar, the pulley, and the inclined plane are simple machines. Complex machines are made up of more than one simple machine. (page 560) Physical Science EXERCISE 5 Simple Machines (page 561) Directions: Choose the best answer for each of the following questions. 1. According to the principle that a little force applied through a great distance can overcome great resistance, which would be most likely to happen if the lever bar in the preceding illustration is increased to 20 feet in length and the weight remained at the end of the bar? Physical Science EXERCISE 5 Simple Machines (page 561) (1) The effort to lift the weight would increase to 150 pounds of applied force. (2) The effort to lift the weight would remain at 100 pounds of applied force. (3) The effort would be decreased by half, to 50 pounds of applied force. (4) The resistance of the weight would double. (5) The resistance of the weight would triple. Physical Science EXERCISE 5 Simple Machines (page 561) 2. What are some other types of household items that could be considered levers? (Hint: Any tool that makes the job easier is likely a lever.) Physical Science The Nature of Heat and Energy Today we know that heat is the result of the random motion of molecules. It is nothing more than energy itself. One theory of physics that has contributed greatly to our understanding of the phenomenon of heat is kinetic theory, a basic theory that explains how different states of matter can exist. (page 561) Physical Science The Nature of Heat and Energy The Kinetic Theory of Matter According to the Kinetic Theory of Matter, matter exists in three states— solid, liquid, or gas. A fourth state, plasma, is an ionized gas; the Sun is made up of plasma. The form, or phase, of matter is determined by the motion of the molecules within it. (page 561) Physical Science The Nature of Heat and Energy The Kinetic Theory of Matter Physical Science The Nature of Heat and Energy The Kinetic Theory of Matter Solids are composed of atoms or molecules in limited motion. These atoms or molecules are in direct contact with one another, allowing little or no space for random movement. The attractive forces of the particles keep the solid intact and give the solid its definite shape and structure. (page 561) Physical Science The Nature of Heat and Energy The Kinetic Theory of Matter In liquids, individual atoms or molecules are able to move past one another into new positions, giving this form of matter its fluidity. Cohesive forces hold liquids intact. (page 561) Physical Science The Nature of Heat and Energy The Kinetic Theory of Matter Gases are substances in which the individual atoms or molecules are in constant random motion. The motion, or kinetic energy, increases along with an increase in temperature. Molecules are unable to hold together, and this property gives gases the ability to flow or spread out to fill the container in which they are placed. (page 562) Physical Science The Nature of Heat and Energy Heat, Temperature, and the States of Matter The state of matter depends on its heat content. Temperature is a measure of heat intensity. The change from one state of matter to another involves the addition or subtraction of a certain amount of heat per gram of substance. (page 562) Physical Science The Nature of Heat and Energy Heat, Temperature, and the States of Matter For example, at 32 degrees Fahrenheit, water, a liquid, changes to ice, a solid. When the temperature is raised above 32 degrees Fahrenheit, the ice, a solid, changes to water, a liquid. At temperatures at or above 212 degrees Fahrenheit, the boiling point of water, the water changes to steam, a gaseous state. Impurities in water affect its freezing point. (page 562) Physical Science The Nature of Heat and Energy Heat, Temperature, and the States of Matter Certain materials expand when their temperatures are raised and shrink when they are lowered. Liquids expand more noticeably than solids, but gases expand even more. The mercury thermometer employs this principle. Temperature can be measured in degrees centigrade or degrees Fahrenheit. (page 562) Physical Science The Nature of Heat and Energy Heat, Temperature, and the States of Matter On the centigrade (or Celsius) scale, 0 degrees represents the freezing point of water, and 100 degrees is the boiling point. On the Fahrenheit scale, 32 degrees represents the freezing point of water, and 212 degrees is the boiling point. (page 562) Physical Science The Nature of Heat and Energy Heat, Temperature, and the States of Matter Temperature is measured in degrees by thermometer, and heat is measured by the calorie or British Thermal Unit (BTU). A calorie is the amount of heat needed to raise one gram of water one degree centigrade. The BTU is the amount of heat required to raise one pound of water 1 degree Fahrenheit. (page 562) Physical Science The Nature of Heat and Energy Heat, Temperature, and the States of Matter Physical Science The Nature of Heat and Energy Heat, Temperature, and the States of Matter Heat is transferred by three methods. The first is called conduction, the transfer of heat between objects that are in direct contact. You have experienced this whenever you have picked up a hot item, such as a handle on a heated pan. The second method is convection. (page 562) Physical Science The Nature of Heat and Energy Heat, Temperature, and the States of Matter This method depends on the currents of water and air. When you are adding hot water to one end of the bathtub filled with water, convection transfers the heat to the rest of the water. The third method is radiation. You can feel waves of heat by putting your hands near a radiator (used to heat many apartments). (page 562) Physical Science The Nature of Heat and Energy Heat, Temperature, and the States of Matter Physical Science EXERCISE 6 Kinetic Theory of Matter (page 563) Directions: Identify the following statements as either true (T) or false (F). 1. ___ There is more rigid molecular structure in a solid than in a gas. 2. ___ An increase in temperature decreases the molecular motion of a gas. 3. ___ Molecules moving past each other in a liquid give it fluidity. 4. ___ Molecules in a gas are close together and exhibit little motion. 5. ___ Heat is transferred by conduction, convection, or coercion. Physical Science EXERCISE 7 Heat and Temperature Directions: Read the passage below and answer the questions that follow. Different materials expand at different degrees of temperature change and in different percentages of their length, volume, or surface. (page 564) Physical Science EXERCISE 7 Heat and Temperature Buckling can occur when a material such as asphalt used for road surfaces reacts to changes in temperature, causing potholes. This is one of the reasons for the widespread use of reinforced concrete (concrete with a steel framework) rather than asphalt on road surfaces and the use of reinforced concrete in high-rise apartment construction. (page 564) Physical Science EXERCISE 7 Heat and Temperature Physical Science EXERCISE 7 Heat and Temperature (page 564) 1. What does the widespread use of reinforced concrete in construction suggest? (1) Concrete and steel expand and contract at nearly the same temperatures. (2) Reinforced concrete expands at temperatures much higher than ordinary asphalt and does not buckle. (3) Reinforced concrete does not expand and contract at all. (4) Asphalt can be used only on roadways and never in construction. (5) Asphalt is much more expensive and harder to use than concrete. Physical Science EXERCISE 7 Heat and Temperature (page 564) 2. Which heat transfer method is demonstrated when your hand is positioned directly over the flame of a lighted candle? (1) convection (2) conduction (3) radiation (4) expansion (5) coersion Physical Science The Nature of Waves A wave is a periodic or harmonic disturbance in space or through a medium (water, for instance) by which energy is transmitted. Water, sound, and light all travel in waves. The illumination a lamp provides comes from light waves (a form of electromagnetic waves) while the music emanating from a stereo comes from sound waves. (page 565) Physical Science The Nature of Waves Wave Physical Science The Nature of Waves The powers to preserve food and warm it come from electromagnetic waves, and the power that transmits signals to a television set comes from radio waves (another form of electromagnetic waves). The energy that gives a waterbed its soothing motion comes from water waves. (page 565) Physical Science The Nature of Waves Types and Properties of Waves Waves transmit energy in different ways, and all phases of matter transmit waves. An example of a solid transmitting wave energy is an earthquake that takes place when rocks are under pressure and snap or slide into new positions. Waves that are felt and seen in water are examples of a liquid transmitting wave energy. (page 565) Physical Science The Nature of Waves Types and Properties of Waves Gases also transmit wave energy, as in an explosion, when heat, sound, and light waves are generated. Two basic types of waves exist: longitudinal waves and transverse waves. (page 565) Physical Science The Nature of Waves Types and Properties of Waves Longitudinal wave Particles of the medium move back and forth in the same direction as the wave itself moves. An example of a longitudinal wave is a sound wave that occurs when a tuning fork is tapped, as shown below. (page 565) Physical Science The Nature of Waves Types and Properties of Waves (page 565) LONGITUDINAL WAVE When a tuning fork is tapped, the prongs move from right to left in a rapid periodic motion. A sound wave is produced, and it moves parallel (right and left) to the moving prong. Physical Science The Nature of Waves Types and Properties of Waves (page 565) Transverse wave Particles of the medium move at right angles to the direction of the wave's movement. An example of a transverse wave is one that occurs when a pebble is tossed into a still pond. Light travels in transverse waves. (Page 565) Physical Science The Nature of Waves Types and Properties of Waves (page 565) TRANSVERSE WAVE When a stone is dropped into a pond, the waves produced appear to move outward. These waves move at right angles to the dropped stone. (page 565) Physical Science The Nature of Waves Waves have two components, a crest and a trough. A crest is the point of highest displacement in a wave, and the trough is the point of lowest displacement. Crests and troughs are easily visible in water waves. (page 566) Physical Science The Nature of Waves Physical Science The Nature of Waves Two specific characteristics of a wave are length and frequency: • Wavelength is defined as the distance between two successive wave crests or two successive wave troughs. • Wave frequency is the number of wave crests that pass a given point per second. (page 566) Physical Science The Nature of Waves Therefore, the shorter the wavelength, the higher the wave frequency. In fact, a wave's speed equals the wavelength times the wave frequency. When a source of a wave is in motion, a compression of the wavelength is detected. This can be demonstrated with sound waves. As a train passes you by while you are standing on the platform, you will notice a distinct drop in the pitch or sound quality. (page 566) Physical Science The Nature of Waves This drop in sound pitch is heard by the observers standing on the side during an automotive race such as the Indianapolis 500. Water waves demonstrate the same compression in the direction of motion. The water waves in the front of a boat are squeezed together, while those at the rear of the boat are far apart. This is referred to as the Doppler Effect. Scientists use the Doppler Effect to forecast tornadoes and to detect the motions of stars in our galaxy. (page 566) Physical Science The Nature of Waves Physical Science The Nature of Waves Sound waves, as illustrated above, are longitudinal waves. A musical pitch, or tone, is heard when there is a definite frequency to a wave. The lower the frequency, the lower the tone. For example, the frequency of a bass speaker in a stereo system is lower than a tweeter, or high-frequency speaker, because the low-pitched sound of the bass results from a lower number of vibrations per second. (page 566) Physical Science The Nature of Waves A sound wave is a wave of compression. It begins at a source—in the case above, a horn speaker. The speaker vibrates, compressing the air in front of it and, like a spring, pushes it away. As the wave passes, the air molecules are forced together. The sensation of hearing results when these waves strike the eardrum. (page 566) Physical Science The Nature of Waves Sound waves can travel through solids, liquids, and gases. In fact, the human body can be a medium for sound waves. Ultrasonic waves, very high-pitched waves, are used in medicine today to detect diseases or to show images of unborn fetuses. (page 566) Physical Science EXERCISE 8 (page 567) Wave Types Directions: In the space provided, write L if the example is an example of a longitudinal wave and T if it is an example of a transverse wave. 1. ____ a wave that can be seen when a loose rope held end to end is jerked at one end 2. ____ the noise caused by the detonation of an atomic bomb 3. ____ the hum created when an arrow is released from a bow 4. ____ waves that appear on the surface of the ocean Physical Science EXERCISE 9 Properties of Waves (page 567) Directions: Look at the illustration below and choose the best answers to the questions that follow. Physical Science EXERCISE 9 Properties of Waves (page 567) 1. According to the illustration above, which points could be used to measure wavelength? (1) T and Y (2) X and Y (3) Z and Y (4) V and W (5) T, X, and U Physical Science EXERCISE 9 Properties of Waves (page 567) 2. The Doppler Effect is used for which of the following purposes? (1) to find fish in lakes (2) to predict storms and tornadoes (3) to test wave frequency (4) to reflect images to satellites (5) to heighten sound in stereos Physical Science The Nature of Light Physicists define light as a form of electromagnetic energy that stimulates sensitive cells of the retina of the human eye to cause perception of vision. Electromagnetic energy can be expressed in wavelength ranges along a continuum, or spectrum. Light occupies the center of a spectrum that ranges from the low end (gamma rays) to the high end (radio waves). (page 568) Physical Science The Nature of Light Electromagnetic Spectrum Physical Science The Nature of Light Electromagnetic Spectrum Physical Science The Nature of Light The other rays that occupy the electromagnetic spectrum are Xrays, ultraviolet rays, and infrared rays. Ultraviolet rays are invisible and are chiefly responsible for sunburn and tan. Heat-emitting objects such as the sun or a radiator send out infrared rays that can be detected only by certain sensitive instruments. (page 568) Physical Science The Nature of Light Electromagnetic Spectrum Physical Science The Nature of Light Electromagnetic Spectrum Physical Science The Nature of Light The visible rays of the spectrum are recognized by the human eye as color. In order, these colors are red, orange, yellow, green, blue, indigo (deep blue), and violet. The shortest wavelengths that we can see are those we call violet; the longest ones are those we call red. (page 568) Physical Science The Nature of Light Two theories about the nature of light exist: the wave theory and the particle theory. These theories seem to oppose each other but really just focus on different properties of light. According to the Wave Theory of Light, light is a luminous energy emitted by a light source and travels through space as a transverse wave. (page 568) Physical Science The Nature of Light According to the Particle Theory of Light, light energy is both radiated (transmitted) and absorbed as tiny packets, or bundles, and not as continuous waves. Atoms and molecules are able to emit or absorb light energy in specific amounts. (page 568) Physical Science EXERCISE 10 The Photoelectric Principle Directions: Read the passage below and answer the question that follows. The electric eye, or photoelectric cell, is a mechanism used to open and close a garage door when a beam of light is activated or broken. The principle of the electric eye is based on the photoelectric effect. (page 569) Physical Science EXERCISE 10 The Photoelectric Principle The photoelectric effect occurs when a beam of light strikes certain metals, causing electrons to be knocked out of the metal, producing an electric current. This is how it happens: (page 569) Physical Science EXERCISE 10 The Photoelectric Principle Light falling on the inside of a bulb coated with an active substance causes electrons to be emitted. The electrons are attracted to a positively charged electrode positioned in the center of the bulb as a filament. An electric current results when the electrons (negatively charged particles) are attracted to the positively charged particles of the electrode. (page 569) Physical Science EXERCISE 10 The Photoelectric Principle It is observed that electrons are knocked loose only when a certain light energy is reached. The current can then be controlled by changes in light intensity. It appears that electrons are able to absorb only a certain amount of light at one time. When light shines on the electric eye, a current is established and the door moves. When the beam of light is broken, the door stops. (page 569) Physical Science EXERCISE 10 The Photoelectric Principle (page 569) How does the principle of the electric eye act? (1) to support the wave theory of light that light comes only from a luminous source (2) to dispute the belief that all light exists only as a continuous wave (3) to support the particle theory of light, which states that light energy is transmitted in packets and bundles and not as waves (4) to complement the idea that light acts like particles in a wave (5) to contradict the idea that light is generated only in a star Physical Science PROPERTIES OF LIGHT WAVES (page 570) Reflection -the angular return of a light wave that occurs when it strikes a shiny surface Example: light bouncing off a mirror Refraction - the apparent bending of light waves as they pass from one medium to another Example: drinking straw looking broken in a glass of water Physical Science PROPERTIES OF LIGHT WAVES (page 570) Diffraction - the bending of light waves according to their wavelengths as they pass near the edge of an obstacle or through a small opening Example: "rainbow" pattern on an old phonograph record held edgewise toward white light Physical Science PROPERTIES OF LIGHT WAVES (page 570) Interference the altering of brightness of light rays that occurs when they interfere with each other, causing reinforcement and cancellation Example: holding thumb and finger together and looking through the opening at a bright light Physical Science PROPERTIES OF LIGHT WAVES (page 570) Polarization - the restriction of light waves to a particular plane, horizontal or vertical Example: sunglasses that minimize glare off shiny surfaces Physical Science EXERCISE 11 Properties of Light Waves (page 570) Directions: Use the information above to choose the best answer for each question below. 1. A coin lying at the bottom of a pool is located at a different point from where the eye perceives it to be. The light rays from the coin bend as they pass from water to air. This demonstrates (1) reflection (2) refraction (3) diffraction (4) interference (5) polarization Physical Science EXERCISE 11 Properties of Light Waves (page 570) 2. Rays of light striking a polished piece of chrome appear to bounce off its surface. This demonstrates (1) reflection (2) refraction (3) diffraction (4) interference (5) polarization Physical Science The Nature of Electricity Electricity is another invisible but vital form of energy that we often take for granted. Without electricity, however, our lives would be paralyzed. The more urbanized we become, the more dependent on electricity we are. Nuclear energy, despite its potential hazards, is an important source for generating the electrical power we need. (page 571) Physical Science The Nature of Electricity Physicists define electricity as a form of energy that results from the flow of loose electrons— electrons weakly bound to atoms. Electricity is closely related to magnetism; therefore, the attractive force of magnetism must be discussed in order to explain electrical energy. (page 571) Physical Science The Nature of Electricity Magnetism and Electrical Charges The points of attraction at opposite ends of a magnet are called its poles. Magnets have a north and a south pole, also called a positive and a negative pole. The opposite poles of two magnets (a north pole and a south pole) will attract each other. Correspondingly, similar poles (two north or south poles) will repel each other. (page 571) Physical Science The Nature of Electricity Magnetism and Electrical Charges The space around magnets is called a magnetic field. Only a few natural and synthetic materials can be magnetized— iron, steel, nickel, cobalt, and some alloys. A magnet, with its poles and lines of force, is illustrated below. (page 571) Physical Science The Nature of Electricity Magnetism and Electrical Charges Physical Science The Nature of Electricity Magnetism and Electrical Charges Physical Science The Nature of Electricity Magnetic Lines of Force Every magnetic substance contains domains, groups of molecules with attractive forces. Before a substance is magnetized, these domains are arranged randomly so that the field of one domain is canceled out by the field of another. When the substance is magnetized, the domains line up parallel to the lines of force, with all north poles facing in the same direction. (page 571) Physical Science The Nature of Electricity Magnetic Lines of Force This arrangement makes a permanent magnet out of a material in which the domains are too weak to disarrange themselves. In most elements the atoms possess a slight magnetic field because of their spinning electrons. (page 571) Physical Science The Nature of Electricity Magnetic Lines of Force However, the fields cancel each other out because the atoms rotate and spin in different directions. In a magnet, however, whole groups of atoms line up in one direction and increase one another's magnetic effect rather than cancel it out. These magnetic concentrations are magnetic domains. (page 571) Physical Science The Nature of Electricity Static Electricity and Magnetism Static electricity is a stationary electrical charge caused by the friction of two objects, one positively charged and the other negatively charged. Static electricity operates on the same principle as magnetism. The rubbing of the carpet by your shoes causes your body to become electrified. (page 572) Physical Science The Nature of Electricity Static Electricity and Magnetism The shock you feel is caused by your negatively charged body being neutralized by the positive charge of the object you touch. Upon contact your body is no longer charged. Static electricity is stored and does not move. The charged object must be brought into contact with another object that has an opposite charge for electrical shock to occur. (page 572) Physical Science The Nature of Electricity Static Electricity and Magnetism Physical Science EXERCISE 12 GED PRACTICE Electricity and Magnetism Directions: Choose the best answer for the questions on page 573, The first question is based on the following paragraph. Physical Science EXERCISE 12 Electricity and Magnetism Earth itself is surrounded by a magnetic field. This may be because of strong electric currents in Earth's core and the rotation of Earth. The north magnetic pole is located in Canada; the south magnetic pole is in nearly the opposite location. The strong magnetic attraction of these poles tends to align the needle of a compass in a northerly-southerly direction. (page 572) Physical Science EXERCISE 12 Electricity and Magnetism (page 573) 1. What makes a compass tell direction? (1) The whole Earth acts as a magnet. (2) The Chinese discovered the magnetic poles. (3) The Greeks discovered the magnetic poles. (4) Large iron deposits are located in Canada. (5) The magnetic attraction of Earth is increasing. Physical Science EXERCISE 12 Electricity and Magnetism (page 573) 2. Which of the following would be attracted to either pole of a magnet? (1) a piece of aluminum (2) a piece of brass (3) a piece of tin (4) an unmagnetized piece of cobalt (5) a magnetized piece of cobalt Physical Science Electric Currents Early scientists who experimented with electric charges found that charges could move easily through certain materials called conductors. As you learned in the chemistry section, metal was found to be a good conductor of electricity, as were salt solutions, acids, and hot gases. Other materials such as rubber were found not to conduct charges at all. These materials are called insulators. (page 573) Physical Science Electric Currents An electric current is created by an electric charge in motion. In a solid conductor, such as wire, the current is a stream of moving electrons. In a liquid or gas, the current may be positively and negatively charged atoms— ions. An electric current flowing through a solid conductor can be compared to the flow of water through the pipes in your plumbing system. (page 573) Physical Science Electric Currents An electric current moves slowly—about a hundredth of an inch per second. Although our lights come on instantly when a switch is turned on, it is because the wires are always filled with electrons, just as a water pipe is always filled with water. (page 573) Physical Science Electromagnets An electromagnet is a core of soft magnetic material surrounded by a coil of wire. An electric current is passed through the wire to magnetize the core when a switch is flicked or a button is pushed. The device then has the power to attract iron objects. When the switch is turned off, the attraction is broken. Electromagnets are used in radios and in ordinary doorbells. (page 573) Physical Science EXERCISE 13 (page 575) Conductors and Insulators Directions: Identify the following terms as either a conductor of electricity (C) or an insulator (I). 1. ________ leather 2. ________ wood 3. ________ salt water 4. ________ plastic 5. ________ copper Physical Science EXERCISE 14 (page 574) Electromagnets Directions: Choose the best answer for the following questions. 1. Why would a radio with a strong electromagnet be placed far away from the navigation instruments on a plane or ship? (1) The radio wouldn't work because of electrical interference. (2) The radio couldn't be heard clearly because of static. (3) The accuracy of the compass would be affected by the magnetic field established by the radio's electromagnet. (4) The radio's electromagnet would cause all the navigation instruments to malfunction. (5) The radio would draw too much electrical energy, causing the electrical system of the ship or plane to discharge. Physical Science EXERCISE 14 (page 574) Electromagnets 2. Identify which of the following are true (T) or false (F). ___ You need an insulator to keep electricity flowing only along wires. ___ Electromagnets are used in doorbells. ___ When the switch is in the off position, electricity still is flowing through the circuit. Physical Science Creating Electricity Electricity is created by power companies and sent to our homes by high voltage wires through transformers. There are several ways to create electricity. Because there is a concern about the limited quantities of fossil fuels, alternative power supplies for electricity are being used. (page 575) Physical Science Creating Electricity One system requires the fission of nuclear energy in nuclear power plants. These plants bombard the nuclei of large unstable uranium atoms with neutrons. The large release of heat is used to heat water, which is used to turn a turbine, a wire loop connecting two magnets. (page 575) Physical Science Creating Electricity When the turbine is forced to turn, the electrons are stolen from the magnets and sent through the wire as electricity. This alternative energy has many drawbacks, including the safe disposal of radioactive nuclear waste left over from the reaction. (page 575) Physical Science Creating Electricity TURBINE Physical Science Creating Electricity TURBINE Physical Science Creating Electricity TURBINE Physical Science Creating Electricity Another alternative is solar energy. Scientists have found that pure silicon (found in sand and one of the most common elements in the crust of the Earth) is electrically excited in the presence of light. You may have experienced this if you own a solar calculator, but it may not have performed in a dimly lighted area. The sun's energy excites the electrons, which then flow along wires to provide electricity to the attached appliance. (page 575) Physical Science Creating Electricity SOLAR ENERGY Physical Science Creating Electricity SOLAR ENERGY Physical Science Creating Electricity SOLAR ENERGY Physical Science Creating Electricity Other alternative energies are limited to the availability of the conditions necessary to generate electricity. One such alternative is wind power, which has been successfully captured through the use of windmills throughout the history of civilization. California has wind farms where many large windmills are connected to generate electricity. (page 576) Physical Science Creating Electricity These new models on the old design limit the number of arms on the mill and make these arms out of durable synthetic materials. Windmills do not need a strong wind; in fact, strong winds can damage the mechanics. The best condition is a steady wind that maintains a continuous motion of the flywheel. (page 576) Physical Science Creating Electricity WIND ENERGY Physical Science Creating Electricity WIND ENERGY Physical Science Creating Electricity WIND ENERGY Physical Science Creating Electricity WIND ENERGY Physical Science Creating Electricity Hydroelectric power is another source that has to be limited to the already established use of the water flow in the region. Many rivers are used as transportation and cannot be dammed to provide the reservoir of water needed to control the flow of water through the turbine system. (page 576) Physical Science Creating Electricity Yet hydroelectric power, as well as wind and solar powers is a clean, renewable resource. Critics suggest that the reason these systems have not been fully developed is the fear energy companies have in reducing their own incomes. (page 576) Physical Science Creating Electricity Hydroelectric power Physical Science Creating Electricity Hydroelectric power Physical Science Creating Electricity Hydroelectric power Physical Science EXERCISE 15 Creating Electricity (page 577) Directions: Use the information above to fill in the blanks in each statement below. 1. Hydroelectric power is not always possible because sometimes rivers are used for _______________. 2. Fossil fuels will not be around forever, so we need to explore the use of other energy systems called _______________. 3. Windmills do not need strong wind, but they do need _______________ wind. 4. Pure silicon has electrons that are excited into motion by _________________. 5. A loop or wire that is turned between two magnets and creates electricity is a _______________.