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Doppler effect
The Doppler effect is the alteration of frequency and wavelength in a wave resulting from the wave source’s motion relative to an observer. A moving sound source causes sound waves to be compressed (higher-pitched) in front of the source (meaning in the direction of movement), and the sound waves will be spread apart behind the source, thereby becoming lower frequency. Most people have experienced this phenomenon directly by being in the vicinity of a moving siren or ambulance. -
Mach Bands
After receiving his doctorate in physics from the University of Vienna in 1860, Mach discovered the human eye’s tendency to see bright or dark bands near the edges of areas with sharply different illuminations1. These lines, although illusory, seem to appear between areas of different gradients and were aptly names “Mach bands” in honor of him1. -
Mach’s principle
The amount and distribution of mass in the universe and the interactions between these particles affects the inertia of each particle. In other words, inertia is a result of the relationship of an object (or the interaction between two bodies, even at enormous distances) to the rest of the matter in the universe. This idea was one of Einstein’s inspirations for the theory of relativity.1 -
Inspiring Einstein
In an 1886 alignment with the empiricist tradition, Mach postulated that “all knowledge is derived from sensation”. He wrote that phenomena can only be understood in terms of sensations (experiences) present in the observation of the phenomena. “No statement is verifiable unless it is empirical1”. He rejected concepts like absolute space and time, and his work paved the way for Einstein’s theory of relativity1. Einstein credits him with inspiration in some of his writings1. -
Key Work
In 1887, Mach established the principles of supersonics and the idea of the “Mach number;” the ratio of an object’s velocity compared to the velocity of sound, expressed as a percentage1. Though perhaps not his most influential and far reaching contribution to science, it is for the Mach number that he is most famous. -
Gestalt theory
Mach founded Gestalt theory, which postulates how the human brain allows us to view objects as a whole instead of their pieces. A maxim is the “Law of Simplicity”. Gestalt theory was the foundation for the modern study of perception and a reaction against what Mach perceived as the “cold” and “sterile” subject of human experience. The theory’s prime tenant is that the whole is greater than its parts. “Gestalt” is a German word meaning the “way a thing is placed or put together”. -
Major Works:
Beiträge zur Analyse der Empfindungen (“Contributions to the Analysis of the Sensations”), 1886 Erkenntnis und Irrtum (“Knowledge and Error”), 1905 -
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