The measure of how often a periodic event occurs, such as a signal going through a complete cycle. Frequency is usually measured in hertz (Hz), with 1 Hz equaling 1 occurrence (cycle) per second. In the United States, household electricity is alternating current with a frequency of 60 Hz. Frequency is also measured in kilohertz (kHz, or 1000 Hz), megahertz (MHz, or 1000 kHz), gigahertz (GHz, or 1000 MHz), or terahertz (THz, or 1000 GHz). See the illustration. Compare wavelength. In physics, the number of periodic oscillations, vibrations, or waves occurring per unit of time. The unit of frequency is the hertz (Hz), one hertz being equivalent to one cycle per second.
Human beings can hear sounds from objects vibrating in the range 20–15,000 Hz. Ultrasonic frequencies well above 15,000 Hz can be detected by mammals such as bats. Infrasound (low frequency sound) can be detected by some animals and birds. Pigeons can detect sounds as low as 0.1 Hz; elephants communicate using sounds as low as 1 Hz.
ETYM Latin frequentia numerous attendance, multitude: cf. French fréquence. Related to Frequent.
In statistics, the number of times an event occurs. For example, when two dice are thrown repeatedly and the two scores added together, each of the numbers 2 to 12 may have a frequency of occurrence. The set of data including the frequencies is called a frequency distribution, usually presented in a frequency table or shown diagramatically, by a frequency polygon.
1. The number of observations in a given statistical category; SYN. absolute frequency.
2. The number of occurrences within a given time period (usually 1 second); SYN. frequence, oftenness.
3. The ratio of the number of observations in a statistical category to the total number of observations; SYN. relative frequency.
The number of cycles over a specified time period over which an event occurs. The reciprocal is called the period.
ETYM Latin velocitas, from velox, -ocis, swift, quick; perhaps akin to volare to fly: cf. French vélocité.
Speed of an object in a given direction. Velocity is a vector quantity, since its direction is important as well as its magnitude (or speed).
The velocity at any instant of a particle traveling in a curved path is in the direction of the tangent to the path at the instant considered. The velocity v of an object traveling in a fixed direction may be calculated by dividing the distance s it has traveled by the time t taken to do so, and may be expressed as.
V = s/t.
1. Quickness of motion; swiftness; speed; celerity; rapidity.
2. Rate of motion; the relation of motion to time, measured by the number of units of space passed over by a moving body or point in a unit of time.
The time rate of change of displacement; dx/dt.