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Chapter Introduction Lesson 1 The Nature of Energy Lesson 2 Waves and Sound Lesson 3 Properties of Light Lesson 4 Electromagnetic Waves Lesson 5 Heat Lesson 6 Electricity Chapter Wrap-Up What are the different forms of energy? The Nature of Energy Essential Question • What forms can energy take and how do they compare? The Nature of Energy Energy Kinetic energy Potential energy Chemical potential energy Elastic potential energy Gravitational potential energy Law of conservation of energy What is energy? • Everywhere around you changes are occurring. – Ex. Electricity into light and heat energy Plants turn sunlight into food You shifting in your seat. • Every change that occurs – whether it is large or small – involves energy. What is energy? (cont.) • Energy is the ability to cause change. • Energy can cause changes in the motions of objects. • Anything that causes change, must have energy. – Ex. You use energy when you travel to school, whether you walk, ride in a car, or take the bus. • Energy is measured in units called joules (J). What is energy? (cont.) • Energy comes in many forms. Forms of Energy Form Nuclear Chemical Electrical Light Mechanical Sound Thermal Example of Source the Sun, radioactive material food a generator, a battery the Sun, an electric lamp moving parts in a machine vibrations of a stereo speaker hot water in a radiator • All forms of energy have one thing in common: they have the ability to cause change. What are kinetic and potential energy? • You know that there are many forms of energy. But all forms of energy can be classified as potential or kinetic energy. • Kinetic energy is the energy of motion. What are kinetic and potential energy? (cont.) • All moving objects have kinetic energy. • The faster an object moves, the more kinetic energy it has. • If two objects move at the same speed, the object with more mass has more kinetic energy. What are kinetic and potential energy? (cont.) • The kinetic energy (KE) of an object depends on its speed and its mass. The vertical bars show the kinetic energy of each vehicle. What are kinetic and potential energy? (cont.) • There are different forms of kinetic energy. – Ex. Electricity is related to kinetic energy of electrons. Sound is the kinetic energy of particles as they move in waves. What are kinetic and potential energy? (cont.) • Energy doesn’t have to involve motion. Even motionless objects can have energy. • Potential energy is the energy stored in an object or a material. – Ex. A rock at the top of a hill. Has the potential to cause change by rolling down the hill. What are kinetic and potential energy? (cont.) • Objects can have a combination of potential and kinetic energy – mechanical energy. – Ex. Roller coasters At the top of the hill – high potential energy and low kinetic energy. Coming down the hill – potential energy decreases and kinetic energy increases. What are the forms of potential energy? • Chemical potential energy is energy stored in the chemical bonds between atoms. – Ex. Food, gasoline What are the forms of potential energy? (cont.) • Elastic potential energy is the energy stored in something that can stretch or compress. – Ex. Spring, rubber band when stretched or compressed What are the forms of potential energy? (cont.) • Gravitational potential energy is the energy stored in objects due to their position above Earth’s surface. • The GPE of an object depends on the object’s mass and height above the ground. – Ex. Dropping a bowling ball from 1m causes a greater change than dropping a tennis ball from 1m. How does energy change? • Energy can change from a potential to a kinetic form • In the world around you, energy is transforming continually between one form and another. How does energy change? (cont.) – Ex. A microwave oven changes electric energy into radiant energy. How does energy change? (cont.) • Energy enables things to move. • Machines and living things need chemical energy – in the form of fuel or food – to get from one place to another. – Ex. Walking or jogging = Muscles change chemical energy from the food you ate into mechanical energy. Moving your car = engine changes chemical energy from fuel into heat. The heat powers the engine in the form of mechanical energy. How does energy change? (cont.) • Energy is also required in manufacturing. – Ex. Clothes, paper, computers, microwaves • Factory machines use electrical or chemical energy to run. • They generate thermal energy as a byproduct of their mechanical movement. Where does energy go? • Law of conservation of energy is a physical law that states that energy may change form but it cannot be created or destroyed. – Ex. Applying the brakes of your bicycle. A moving bicycle has mechanical energy. • When you apply the brakes that energy is not lost or destroyed, it is transformed into thermal energy from the friction between the brake pad and the wheel. Where does energy go? (cont.) • In the example before, the mechanical energy to move the bike came from chemical energy in your muscles. • The chemical energy in your muscles came from the food you ate. • The chemical energy in the food ate came from the Sun. – Where did the Sun’s energy come from? Where does energy go? (cont.) • The Sun’s energy is generated through a process called nuclear fusion. • Nuclear fusion occurs when the Sun and other stars convert a tiny amount of mass into an enormous amount of energy. Where does energy go? (cont.) • Nuclear power is generated on Earth by nuclear power plants. • These power plants split atoms in a process called nuclear fission. Where does energy go? (cont.) • A tremendous amount of thermal energy is released during nuclear fission. When is heat “lost”? • Many chemical reactions will not occur without heat. • Sometimes this heat is an unwanted waste product. – Ex. Heat generated by friction causes many machines, like your car, to break. Friction and heat wear down machine parts. If this heat, cannot be released, your car will stop working. Where would a book have the most potential energy? A. on the floor B. on the top shelf of a bookcase C. on the middle shelf of a bookcase D. on the lowest shelf on a bookcase Which type of energy increases when you compress a spring? A. elastic potential energy B. kinetic energy C. chemical potential energy D. gravitational potential energy Which term refers to energy due to motion? A. kinetic energy B. potential energy C. sound energy D. stored energy Waves and Sound Essential Question • How to waves cause sound? Waves and Sound Wave Frequency Wavelength Sound wave Amplitude Reflection What are waves? • Wave is a disturbance that transfers energy from one point to another. • Electromagnetic waves can travel through empty space and matter. – Ex. Light waves What are waves? (cont.) • Mechanical waves must travel through a medium – a substance – in order to transfer energy – Ex. Sound waves • A medium can be a solid, liquid or gas. • The movement of particles by a wave is called a vibration. What are waves? (cont.) • Waves are classified by the type of vibration they cause in a medium. – Transverse waves – when a transverse wave travels through a medium, matter moves up and down as the wave travels through it. • Ex. Water waves What are waves? (cont.) – Compressional wave– when a compressional wave travels, matter moves back and forth as the wave travels through it. • Similar to a spring or a slinky. • Ex. Sound waves What are waves? (cont.) • All waves travel and transfer energy from one point to another, with little or no displacement of the particles of the medium. • After the wave has passed, the particles end up in about the same position they started in. How can you measure waves? • Wavelength is the distance between two waves’ crests or two waves’ troughs. • OR The distance between two waves’ compressions or rarefactions. How can you measure waves? • Amplitude is the height of a wave from its trough or crest to its midpoint. How can you measure waves? • The wave with the larger amplitude carries more energy and makes the ball bounce higher. How can you measure waves? (cont.) • Frequency is a measure of how many wave crests or troughs pass a given point in one unit of time. – High-frequency waves have shorter wavelengths and transfer greater energy. How can you measure waves? (cont.) • The period of a wave is the amount of time it takes for a wave to complete one full cycle. • Frequency is measured in hertz (Hz), the number of waves per second. – Ex. 5 waves in 20seconds. 5 ÷ 20 = 0.25 Hz. How can you measure waves? (cont.) • The distance a wave travels per second determines its speed. – Ex. A boat passes within 65m of a buoy. The waves from the boat take 5seconds to reach the buoy. Wave speed = 65 ÷ 5 = 13m/s • The speed of a wave depends on its medium, not its frequency! – Ex. A high-frequency wave can travel slowly How does sound travel? • Sound wave is a compressional wave produced by vibrations in matter. • Molecules in the medium moved back and forth, pushing nearby molecules. • Because sound waves depend on the compression of matter, they need a medium to travel through. How does sound travel? (cont.) • In sound waves, the distance between the particles affects speed. • Sound waves move fastest through solids, slower through liquids and slowest through gases. Medium Air Speed (in m/s) 334 Freshwater 1,461 Seawater 1,490 Silver 2,610 Glass 5,000 How does sound travel? (cont.) • When you look in a mirror, light waves bounce off the mirror into your eyes and enable you to see your image. • Sound waves also reflect off of objects. • Reflection is the bouncing of a wave off an object, changing the direction of travel. – Ex. An echo and sonar How does sound travel? (cont.) • The material a sound wave strikes affects how the sound wave moves. • Hard surfaces reflect sound waves, soft surfaces absorb sound waves. – Absorption is the transfer of energy when a wave disappears into a surface. • Ex. Ceiling tiles, insulation • A material that absorbs sound waves well does not reflect sound waves. What are properties of sound? • The pitch or the highness or lowness of a sound, depends on the frequency of the sound waves. – High pitched sounds have a high frequency – Low pitched sounds have a low frequency • Most humans can hear sound waves in the range of about 20Hz to about 20,000Hz. What are properties of sound? (cont) • A sound’s pitch seems to change if its source or listener is moving. – This is called the Doppler effect. What are properties of sound? (cont) • The difference in the loudness of a sound is called volume. • The amount of energy, or intensity (amplitude), of the sound wave determines the volume of a sound. – The larger the amplitude, the louder the sound. What are properties of sound? (cont) • The volume of a sound is measured in units called decibels (dB) – Regular speech have a volume of about 60dB. – Sounds greater than 90dB can damage people’s hearing. What are properties of sound? (cont) • The motion of two or more waves passing through the same medium at the same time is called interference. – Ex. Two sets of speakers playing the same song in the same room. What are properties of sound? (cont) • Interference can be positive for negative. – If the crests or troughs of the waves meet, they would combine and the combined sound would be louder – constructive interference. – If the crest of one wave meets the trough of another wave, combined amplitude is lower than the sound made by one source alone – destructive interference. How do we hear music? • Sound waves pass through your ear canal to your eardrum causing your eardrum to vibrate. • The vibrations stimulate nerve cells located deep inside the ear. • These vibrations are then converted to nerve impulses that your brain recognizes and identifies as different sounds. How do we hear music? (cont.) How do we hear music? (cont.) • Music is a combination of sounds that a listener finds pleasing. • Noise is a combination of sounds that a listener finds unpleasant. Which occurs when waves that overlap combine to form a new wave? A. diffraction B. interference C. reflection D. refraction To measure the wavelength of a transverse wave, you can measure the distance from one crest to which of these? A. the next crest B. the next trough C. the next compression D. the next rarefaction Which refers to the number of wavelengths that pass by a point each second? A. amplitude B. compression C. frequency D. wavelength Properties of Light Essential Question • How does light move and change? Properties of Light Transparent Translucent Opaque Law of reflection Refraction How does light travel? • Light is a form of energy that travels in waves. • Light waves spread out as they move away from a source. • Light travels in straight lines called rays. How does light travel? (cont.) • Light waves can carry energy through space and some matter. • Light travels through space at the fastest speed matter and energy can possibly reach: about 300,000 km/s • A light ray will not change direction unless it travels through a different medium or is disturbed in some way. How does light travel? (cont.) • Transparent allowing light to pass through with almost no distortion. • Objects look clear and crisp behind transparent material. • Ex. Lens in eyeglasses How does light travel? (cont.) • Translucent allowing some light to travel through and blocking some light or bouncing it in a different direction. – Objects appear blurred behind translucent material. – Ex. Stained glass, lampshades How does light travel? (cont.) • Opaque not allowing light to pass through. – Object is not seen behind opaque material. – Casts a shadow when it is in front of a light source. – Ex. Books, walls, glass of milk How does light act with mirrors? • Law of reflection is a physical law that states that the angle between an incoming light ray and a surface is equal to the angle between the reflected light ray and the same surface. How does light act with mirrors? (cont.) • Any surface that reflects light and forms images is a mirror. – Plane mirror – has a flat surface. The images appear to be exact copies, though they are reversed. How does light act with mirrors? (cont.) – Concave mirror • has a surface that curves inward. • Light rays are reflected and meet at a point located in front of the mirror dependent on the curve of the mirror. • An object placed close to a concave mirror will produce a large image that right-side-up. • As you move the object away, the image will become blurry, smaller and eventually appear upside down. How does light act with mirrors? (cont.) – Concave mirror (cont.) • Are used to gather light inside of telescopes. • Used in make-up or shaving mirrors – to make the face appear larger and in more detail. How does light act with mirrors? (cont.) – Convex mirror • has a surface that curves outward. • Light rays are reflected from the surface and spread out, producing a wide-angle view. • Always produces an image that is right-side-up and much smaller than the object. How does light act with mirrors? (cont.) – Convex mirror (cont.) • Useful for security in stores and providing a better view for drivers of vehicles. What is refraction? • Light always travels through empty space at the same speed – 300,000km/s • However, light travels slower when it moves through a medium, such as air, glass or water. What is refraction? (cont.) • Refraction is the change in direction of a wave because of a change in the medium it is traveling through. • When light moves into a medium where its speed decreases, the ray bends toward the normal. What is refraction? (cont.) • When light moves into a medium where its speed increases, the ray bends away from the normal. • The larger the change in speed of the light wave is, the larger the change in direction is. What is refraction? (cont.) • A lens is a transparent object with at least one curved side that causes light to change direction. • Light refracts as it passes through a lens. • The greater the curve of the lens, the more the light refracts. What is refraction? (cont.) • A lens that is thicker in the middle than at the edges is a convex lens. • A lens that is thicker at the edges than in the middle is a concave lens. What is refraction? (cont.) • A convex lens refracts light inward and it converges. • If the object is located between the lens and its focal point, the image is right-side-up and larger than the object. • If the object is located beyond the focal point, the image is upside down and smaller than the object. What is refraction? (cont.) • A concave lens refracts light rays apart. It diverges. • A concave lens is thinner in the middle than it is at the edges. • The image is always right-side-up and smaller than the actual object. How is light refracted by telescopes and cameras? • Much of what is known about the universe has come from images and other information gathered by telescopes. • A telescope is a device that collects light and magnifies images to make distant objects appear closer. • Telescopes use mirrors and lenses to gather light. How is light refracted by telescopes and cameras? • Refracting telescopes use two convex lenses to form an image of a distant object. • Light passes through an objective lens that forms an image. • The image is then magnified by a lens in the eyepiece. How is light refracted by telescopes and cameras? • Reflecting telescopes have a concave mirror instead of a concave objective lens to gather light. • The large concave mirror focuses light onto a secondary mirror that directs it to the eyepiece, which magnifies the image. How is light refracted by telescopes and cameras? • Cameras have a lens or a system of lenses that converge light rays toward a sensor. • On some cameras, you can zoom, or make the image larger, by moving the lenses, which changes the focal length of the lens and lets you photograph distant and close objects. How can we correct vision? • The internal shape of your eyes plays a role in how they function. • If your eye shape is even slightly off, your vision will be impaired. How can we correct vision? (cont.) • A nearsighted person has at least one eye that is longer than normal from front to back. • This causes light rays from distant objects to be focused in front of the retina. As a result nearby objects are clear but distant objects look blurry. How can we correct vision? (cont.) • Concave lenses spread the light rays before they reach the eye so the rays travel a longer distance and focus at the correct spot. How can we correct vision? (cont.) • A farsighted person has at least one eye that is shorter than normal from front to back. • This causes light rays from nearby objects to be focused in behind the retina. As a result, distant objects are clear but nearby objects look blurry. How can we correct vision? (cont.) • Convex lenses bend the light rays closer together before they reach the eye so the rays are focused properly on the retina. A material that allows most of the light that strikes it to pass through and form a blurry image is called what? A. luminous B. opaque C. transparent D. translucent Which is a mirror that curves inward? A. concave mirror B. convex mirror C. plane mirror D. virtual mirror Which term refers to a lens that is thicker in the middle than at the edges? A. concave lens B. convex lens C. prism D. rod Electromagnetic Waves Essential Question • How do the types of electromagnetic waves compare?