This is optical aliasing, caused by the fact that the frame rate of the movie camera (24 frames per second) is not fast enough to resolve the positions of the spokes.
The generation of aliases is called aliasing.Īn example of aliasing sometimes occurs in motion pictures, as for instance when the wagon wheels in a Western seem to be going backward. If, however, the sampling frequency is less than twice as high as the highest frequency to be sampled, the sampled waveform will contain extraneous components called “aliases”. As long as the sampling frequency is more than twice as high as the highest frequency in the signal, the sampled waveform will be a proper representation of the analog waveform. To digitize an analog signal for processing in digital instruments such as FFT analyzers, it first must be periodically sampled, and the sampling process occurs at a specific rate called the sampling frequency. The procedure for calculating the FFT spectrum is an algorithm. In digital computers, algorithms for different purposes are stored and called into play when needed for certain operations. response”.Īn algorithm is simply a specific procedure for solving a mathematical problem. Most common accelerometers respond down to one or two hertz, and some special accelerometers respond all the way down to zero frequency, sometimes called “D. The high-frequency response of an accelerometer is limited by its inevitable internal mechanical resonance. The value of G amounts to 32.2 feet per second per second.Ī transducer whose electrical output is directly proportional to acceleration over a fairly wide frequency range. This causes some undue complexity in converting parameters between acceleration, velocity, and displacement. It is interesting to note that the G is not actually a unit of acceleration, but is the magnitude of the acceleration due to gravity at the earth’s surface. The time rate of change of velocity, usually measured in Gs in the English system of measurements, and in meters per second per second (m/s 2) in the SI system.
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