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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.
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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.
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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.
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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.
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