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Name ______________________________ Class ___________________ Date __________________ What Is Energy? • Energy is the ability to do work, and work equals the transfer of energy. Energy and work are expressed in units of joules (J). • Kinetic energy is energy of motion and depends on speed and mass. • Potential energy is energy of position. Gravitational potential energy depends on weight and height. • Mechanical energy is the sum of kinetic energy and potential energy. • Thermal energy and sound energy can be considered forms of kinetic energy. • Chemical energy, electrical energy, and nuclear energy can be considered forms of potential energy. Energy Conversions • An energy conversion is a change from one form of energy to another. Any form of energy can be converted into any other form of energy. • Kinetic energy is converted to potential energy when an object is moved against gravity. • Elastic potential energy is another example of potential energy. • Your body uses the food you eat to convert chemical energy into kinetic energy. • Plants convert light energy into chemical energy. • Machines can transfer energy and can convert energy into a more useful form. What Is Heat? • Heat is energy transferred between objects that are at different temperatures. • Thermal energy is the total kinetic energy of the particles that make up a substance. • Conduction, convection, and radiation are three ways thermal energy is transferred. Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor. Holt Science and Technology 29 Energy and Energy Resources Name ______________________________ Class ___________________ Date __________________ The Nature of Waves • A wave is a disturbance that transmits energy. • The particles of a medium do not travel with the wave. • Mechanical waves require a medium, but electromagnetic waves do not. • Particles in a transverse wave vibrate perpendicularly to the direction the wave travels. • Particles in a longitudinal wave vibrate parallel to the direction that the wave travels. Properties of Waves • Amplitude is the maximum distance the particles of a medium vibrate from their rest position. • Wavelength is the distance between two adjacent corresponding parts of a wave. • Frequency is the number of waves that pass a given point in a given amount of time. • Wave speed can be calculated by multiplying the wave’s wavelength by the frequency. Wave Interactions • Waves reflect after hitting a barrier. • Refraction is the bending of a wave when it passes through different media. • Waves bend around barriers or through openings during diffraction. • The result of two or more waves overlapping is called interference. • Amplitude increases during constructive interference and decreases during destructive interference. What Is Sound? • All sounds are generated by vibrations. • Sounds travel as longitudinal waves consisting of compressions and rarefactions. • Sound waves travel in all directions away from their source. • Sound waves require a medium through which to travel. Sound cannot travel in a vacuum. • Your ears convert sound into electrical impulses that are sent to your brain. • The speed of sound depends on the medium and the temperature. • The pitch of a sound becomes higher as the frequency of the sound wave becomes higher. Frequency is expressed in units of Hertz (Hz), which is Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor. Holt Science and Technology 30 Energy and Energy Resources Name ______________________________ Class ___________________ Date __________________ equivalent to waves per second. • The Doppler effect is the apparent change in frequency of a sound caused by the motion of either the listener or the source of the sound. • Loudness increases with the amplitude of the sound. Loudness is expressed in decibels. • The amplitude and frequency of a sound can be measured electronically by an oscilloscope. • Echoes are reflected sound waves. • Some animals can use echolocation to find food or to navigate around objects. • People use echolocation technology in many underwater applications. • Ultrasonography uses sound reflection for medical applications. • Sound barriers and shock waves are created by interference. What Is Light? • Light is an electromagnetic (EM) wave. An EM wave is a wave that consists of changing electric and magnetic fields. EM waves require no matter through which to travel. • EM waves can be produced by the vibration of charged particles. • The speed of light in a vacuum is about 300,000,000 m/s. • EM waves from the sun are the major source of energy for Earth. The Electromagnetic Spectrum • All electromagnetic (EM) waves travel at the speed of light. EM waves differ only by wavelength and frequency. • The entire range of EM waves is called the electromagnetic spectrum. • Radio waves are used for communication. • Microwaves are used in cooking and in radar. • The absorption of infrared waves is felt as an increase in temperature. • Visible light is the narrow range of wavelengths that humans can see. Different wavelengths are seen as different colors. • Ultraviolet light is useful for killing bacteria and for producing vitamin D in the body. Overexposure to ultraviolet light can cause health problems. • X rays and gamma rays are EM waves that are often used in medicine. Overexposure to these kinds of rays can damage or kill living cells. Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor. Holt Science and Technology 31 Energy and Energy Resources Name ______________________________ Class ___________________ Date __________________ Interactions of Light Waves • The law of reflection states that the angle of incidence is equal to the angle of reflection. • Things that are luminous can be seen because they produce their own light. Things that are illuminated can be seen because light reflects off them. • Absorption is the transfer of light energy to particles of matter. Scattering is an interaction of light with matter that causes light to change direction. • Refraction of light waves can create optical illusions and can separate white light into separate colors. • How much light waves diffract depends on the light’s wavelength. Light waves diffract more when traveling through a narrow opening. • Interference can be constructive or destructive. Interference of light waves can cause bright and dark bands. Light and Color • Objects are transparent, translucent, or opaque depending on their ability to transmit light. • Colors of opaque objects are determined by the color of light that they reflect. • Colors of translucent and transparent objects are determined by the color of light they transmit. • White light is a mixture of all colors of light. Mirrors and Lenses VOCABULARY CONCAVE, CONVEX, PLANE/FLAT, MIRROR, REFLECTION, LENS, REFRACTION Light and Sight • The human eye has several parts, including the cornea, the pupil, the iris, the lens, and the retina. • Nearsightedness (use a concave lens) when you can’t see far away and farsightedness (use a convex lens) when you can’t see close up. In both cases, light is not focused on the retina correctly. Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor. Holt Science and Technology 32 Energy and Energy Resources