D
- dark matter
matter that does not emit radiation that astronomers can detect (p. 855)
- decibel
a unit that compares the intensities of different sounds (p. 515)
- decomposition reaction
a chemical reaction in which a compound breaks down into two or more simpler substances (p. 200)
- deflation
the process that occurs when wind picks up and removes surface material (p. 723)
- delta
a mass of sediment deposited at the mouth of a river where the river enters a large body of water (p. 716)
- density
the ratio of a material's mass to its volume (p. 17)
- density currents
currents caused by differences in the density of ocean water (p. 727)
- deposition
the phase change in which a gas or vapor changes directly into a solid without first changing into a liquid (p. 91); the placement of sediment that has been transported from another location (p. 713)
- desert
an extremely dry region (p. 780)
- destructive interference
the interaction among two or more waves in which displacements combine to produce a wave with a smaller displacement (p. 511)
- dew point
the temperature at which air becomes saturated with water vapor (p. 761)
- diffraction
the bending of a wave as it moves around an obstacle or passes through a narrow opening (p. 510)
- diffuse reflection
reflection that occurs when parallel light waves strike a rough, uneven surface and reflect in many different directions (p. 547)
- digital signal
a signal that encodes information as a string of 1's and 0's (p. 619)
- dike
a structure formed when magma hardens in a crack that cuts across rock layers (p. 696)
- diode
a solid-state component with an n-type semiconductor joined to a p-type semiconductor (p. 621)
- direct current (DC)
a flow of electric charge in only one direction (p. 604)
- direct proportion
a relationship between two variables in which their ratio is constant (p. 23)
- dispersion
the process of dissolving by breaking into smaller pieces (p. 230), the process in which white light separates into colors (p. 551)
- dissociation
the separation of ions in an ionic compound as the compound dissolves (p. 229)
- distance
the length of the path between two points (p. 329)
- distillation
a process that separates the substances in a solution based on their boiling points (p. 50)
- divergent boundary
a boundary at which tectonic plates move away from each other (p. 682)
- Doppler effect
a change in sound frequency caused by motion of the sound source, motion of the listener, or both (p. 516)
- double-replacement reaction
a chemical reaction in which two compounds exchange positive ions and form two new compounds (p. 203)
- dunes
deposits formed from windblown sand (p. 724)
E
- earthquake
a movement of Earth's crust that occurs when rocks in the crust suddenly shift, releasing stored energy (p. 684)
- eclipse
event that occurs when the shadow of one body in space, such as a planet or moon, falls on another (p. 799)
- ecliptic plane
the plane in space containing Earth's orbit (p. 792)
- efficiency
the percentage of the work input that becomes work output in a machine (p. 425)
- elastic potential energy
the potential energy of an object that is stretched or compressed (p. 450)
- electric charge
a property that causes subatomic particles such as protons and electrons to attract or repel one another (p. 600)
- electric circuit
a complete path through which electric charge can flow (p. 609)
- electric current
a continuous flow of electric charge (p. 604)
- electric field
a field in a region of space that exerts electric forces on charged particles; a field produced by electric charges or by changing magnetic fields (pp. 533, 602)
- electric force
the attraction or repulsion between electrically charged objects (p. 601)
- electric motor
a device that uses an electromagnet to turn an axle (p. 639)
- electric power
the rate at which electrical energy is converted to another form of energy (p. 611)
- electrical conductor
a material through which electric charge can flow easily (p. 605)
- electrical energy
the energy associated with electric charges (p. 452)
- electrical insulator
a material through which charge cannot flow easily (p. 605)
- electrolyte
a compound that produces ions when it dissolves (p. 249)
- electromagnet
a solenoid with a ferromagnetic core (p. 637)
- electromagnetic energy
a form of energy consisting of changing electric and magnetic fields (p. 452)
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