## Physics Vocab.

##### Created by:

supersam28  on May 29, 2010

chapter 19-24

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# Physics Vocab.

 Harmonic motionmotion that repeats
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#### Definitions

Harmonic motion motion that repeats
Cycle the unit of motion that repeats over and over (ex. A bicycle wheel, a full back-and-forth swing of a swing)
Oscillation a motion that repeats regularly, usually indicating slow motion
Oscillator a system with harmonic motion
Vibration another word used for a motion that repeats regularly, usually indicating fast motion
Frequency the number of cycles per second
Hertz the unit of one cycle per second, which measures frequency
Period the time for one cycle to occur
Amplitude describes the 'size' of a cycle
Damping the gradual loss of amplitude of an oscillator
Phase tells you exactly where an oscillator is in its cycle; measured relative to the whole cycle, and is independent of amplitude or period; measured in degrees
Equilibrium the central position; the system at rest, undisturbed, with zero net force
Restoring force any force that always acts to pull the system back toward equilibrium
Natural frequency the frequency or period at which a system naturally oscillates; every system has one
Resonanceoccurs when a periodic force has the same frequency as the natural frequency of the system; 3 steps: periodic force, system, and response; occurs when: there is a system in harmonic motion like a swing, there is a periodic force like a push, the frequency of the periodic force matches the natural frequency of the system
Wave an oscillation that travels from one place to another
Transverse wave that has its oscillations perpendicular to the direction the wave moves
Longitudinal wave that has vibrations in the same direction as the wave moves
Crest the high point of the wave
Trough the low point of the wave
Wavelength the distance from any point on a wave to the same point on the next cycle of the wave; represented by Lambda (λ)
Standing wave a wave that is confined in a space
Fundamental the lowest natural frequency
Harmonics natural frequencies found on a vibrating string; 'bumps' on the string
Nodes points on a vibrating string where the string does not move
Antinodes points on a vibrating string with the greatest amplitude
Propagate spreading out from where something began
Plane wave straight waves that move in a line perpendicular to the crest of the wave; caused by disturbing the line
Wave fronts a pattern of parallel straight lines formed by the crests of a plane or circular waves
Circular wave waves that move outward in a circle from the center; started by disturbing a single point, radiating outward from the center; create circular wave fronts
Reflection the wave bounces and goes in a new direction
Refraction the wave bends as it passes into and through an object
Diffraction the wave bends around an object or through holes in the object
Absorption the wave is absorbed and disappears
Boundaries an edge or surface where things change suddenly; where conditions or materials change, affecting the wave
Superposition Principle states that the total vibration at any point is the sum of the vibrations from each individual wave
Interference happens when two or more waves mix together
Wave pulse a short length of wave, maybe just a single oscillation
Constructive interference occurs when waves add up to make a larger amplitude; useful in working with light and sound
Destructive interference occurs when waves add up to make a wave with smaller or zero amplitude
Pitch how you hear and interpret a sound's frequency
Decibels the measurement of loudness of sound
Acoustics the science and technology of sound
Subsonic objects that move slower than sound
Supersonic objects that move faster than sound
Shock wave a cone shaped wave that forms where the wave fronts pile up; in front of the wave there is total silence, behind the wave you can hear the noise from the plane, right at the wave the amplitude changes abruptly, causing a sonic boom
Doppler effect occurs when a sound source is moving at speeds below the speed of sound, when an observer hears the frequency at which wave fronts arrive at his or her hears
Reverberation a multiple echo caused by the reflected sound and direct sound together; can make good and bad sounds depending on the effect
Fourier's theorem states that a wave of any shape can be made by adding up single frequency waves
Frequency spectrum a graph showing the different frequencies present in a sound; vertical axis tells you the loudness and the horizontal axis tells you the frequency
Sonogram shows how loud sound is at different frequencies over a period of time
Cochlea a tiny fluid-filled organ in the inner ear where we get our sense of hearing
Rhythm a regular time pattern in a sound
Musical scale a pattern of frequencies that creates most of music
Note each frequency in a musical scale
Octave the range between any frequency and twice that frequency
Harmony the study of how sounds work together to create effects desired by the composer
Beat the sound when two frequencies of sound are close but not exactly equal; useful for determining if an instrument is out of tune
Consonance the sound of more than one frequency of sound and the combination sounds good
Dissonance the sound of more than one frequency of sound and the combination sounds bad
Incandescence the process of making light with heat
Fluorescence the process of atoms releasing electrical energy as light
Intensity the amount of light energy per second falling on a surface
White light light without any color; the combination of all the colors
Photoreceptors light-sensitive cells on the surface of the retina; when light hits it, the cell releases a chemical signal that travels along the optic nerve to the brain, where the signal is translated into a perception of color; signal that is sent depends on how much energy the light has
Cones photoreceptors that respond to color; three types that respond best to red, green, and blue
Rods photoreceptor that responds only to differences in intensity; detect black, white, and shades of gray; more sensitive than other cone cells especially in low light levels
Additive color process where three photoreceptors (red, green, blue) in the eye operate together so that we see millions of different colors; the color seen depends on how much energy is received by each of the 3 cone cells
Additive primary colors red, green, blue
Subtractive color process process where chemicals known as pigments in the dyes and paints absorb some colors and reflect other colors; used in colored fabrics, paints, etc.
Pigments chemicals in dyes that work by taking away colors from white light, absorbing some colors and reflecting other colors
Subtractive primary colors cyan, magenta, yellow; when added make black, which is the absence of color
CMYK color processanother name for the subtractive color process, made up of the colors cyan, magenta, yellow, and black; used for making all colors that are seen in reflected light, including printing inks and fabric dyes; the three pigments are combined in various proportions to make any color, all together making black
RGB color process an additive process that used red, green and blue light; used by television screens and computer monitors
Optics the study of how light behaves
Light ray an imaginary line that represents a thin beam of light
Converging lens (convex lens) lens that bends light so that the light rays come together to a point
Diverging lens (concave lens) lens that bends light so it spreads light apart instead of coming together; items appear smaller
Prism an optical device made of a solid piece of glass with flat polished surfaces; can both bend and/or reflect light; used in telescopes, cameras, and supermarket laser scanners; ex.) diamond
Translucent if some light can pass through an object but the light is scattered in many directions (Ex. Tissue paper, frosted glass)
Transparent materials that allow light to pass through (ex. Glass, plastic, air)
Specular reflection where each ray of light bounces off in a single direction; created on polished surfaces, where you see the reflections of other things but not the surface itself
Diffuse reflection where a single ray of light scatters into many directions due to a surface that is not shiny; caused by the roughness of a surface, even on microscopic level; when looked at, you see the surface itself
Incident ray the light ray that strikes the object
Reflected ray the light ray that bounces off the object
Normal line an imaginary line between the incident and reflected rays, that is perpendicular ot the surface of the object
Angle of incidence the angle between the incident ray and the normal line
Angle of reflection the angle between the normal line and the reflected ray
Ray diagram an accurately drawn sketch showing how light rays interact with mirrors, lenses, and other optical devices
Index of refraction (n) measures the ability of the material to bend light
Angle of refraction the angle between the refracted ray and the normal line
High index to low index bends away from normal line
Low index to high index bends toward normal line
Total internal reflection the effect when the angle of incidence increases, there is a point at which the light will not enter the air but reflect back into the object; occurs when the angle of incidence is greater than the critical angle for a material
Critical angle the angle of incidence at which the angle of refraction is 90 degrees; depends on the index of refraction of the material; at angles of incidence greater than this angle for a material, total internal reflection occurs
Fiber optics thin glass fibers that use total internal reflection to carry light, even around bends and corners; this technology is important to the communications industry
Dispersion describes how refractive index varies depending on the color of light
Objects real physical things that give off or reflect light rays
Images 'pictures' of objects that are formed in space where light rays meet; formed by our eyes, mirrors, lenses, prisms, and other optical devices
Virtual image the image in a mirror, where the light rays do not actually come together to form the image, they only appear to come together; the illusion is created by our eyes and brain
Optical axis the imaginary line that goes through the center of the lens; light traveling along this line is not bent at all by the lens
Focal point a point where light rays that enter a converging lens parallel to its axis bend to meet; there will always be two, on either side of the lens
Focal length the distance from the center of the lens ot the focal point; usually the same for both focal points of a lens
Real image light from each single point on an object comes back together again at a single point in another place to make an image, formed by a converging lens
Focus the place where the light comes together again; where you see the image clearly
Magnification the ratio of the size of the image divided by the size of the object; makes images smaller, larger or equal to life size
Refracting telescope has two converging lenses with different focal lengths; used by microscopes and telescopes to get a higher magnification
Electromagnetic wave waves produced by oscillations of electricity or magnetism
Electromagnetic spectrum the entire range of electromagnetic waves, including all possible frequencies
Radio waves the lowest-frequency waves; wavelengths: kilometers to tens of centimeters; need to be high to efficiently create the large wavelengths they use; (ex. Broadcast towers)
Microwaves range from 30 cm to about 1 mm; often are tuned to the natural frequency of liquid water molecules (ex. Microwaves, cell phones)
Infrared light wavelength: from 1mm to 700nm; often referred to as radiant heat; although we cannot see them, we can feel them with our skin (ex. Infrared waves, heat from the sun)
Visible light wavelength: 700 to 400 nm; includes all the colors of light we see when white light is split by a prism; the term 'light' commonly refers to this part of the spectrum; comes from the sun
Ultraviolet light wavelength: 10 to 400 nm; has enough energy to remove electrons and break chemical bonds (ex. Sunlight, can be beneficial and dangerous to humans; most blocked by ozone layer)
X-rays high-frequency waves used extensively in medical and manufacturing applications; wavelength: 10 nm to .001 nm (ex. X-rays)
Gamma rays generated in nuclear reactions; can push even the inner electrons right out of an atom and completely disrupt chemical bonds; wavelength: less than about ten-trillions of a meter; very dangerous without a heavy shield
Double Slit experiment (Thomas young) famous experiment that gave strong evidence that proved that light is a wave due to an interference pattern can lonely be created by the addition of waves; showed that two beams of light could interfere with each other by letting light pass through tow very thin slits, where light fell on the screen
Diffraction grating creates an interference pattern similar to the pattern for the double slit; a series of thin parallel grooves on a piece of glass or plastic; when light goes through, each groove scatters the light so the grating acts like many parallel slits
Central spot a bright spot that appears directly in front of a diffraction grating where the light passes straight through
Diffraction pattern a series of bright spots on either side of the central bright spot; closest bright spots are called first order
Polarizer a material that allows light of only one polarization to pass through; light that comes through has only one polarization making it polarized light
Polarization the orientation of light, either horizontal or vertical (based on the direction of the oscillation of the wave perpendicular to the direction the wave moves
Photons little bundles of divided light waves; described as 'particle-like'; each atom that makes light gives; absorbs only one at a time
Photoluminescence the process of releasing stored light energy

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