Showing posts with label Mach. Show all posts
Showing posts with label Mach. Show all posts

Nov 30, 2019

What's in a Name, Mach

Ernst Waldfried Josef Wenzel Mach (d.1916) was an Austrian physicist and philosopher, noted for his contributions to physics such as study of shock waves. The ratio of one's speed to that of sound is named the Mach number in his honor.

Mach's main contribution to physics involved his description and photographs of spark shock-waves and then ballistic shock-waves. He showed when a bullet or shell moved faster than the speed of sound; it created a compression of air in front of it. Using schlieren photography, he and his son Ludwig were able to photograph the shadows of the invisible shock waves.

In homage, his name was given to: Mach, a lunar crater; Mach bands, an optical illusion; Mach number, the unit for speed relative to the speed of sound.

During the 1860s he discovered the physiological phenomenon that has come to be called Mach’s bands, the tendency of the human eye to see bright or dark bands near the boundaries between areas of sharply differing illumination.

May 17, 2013

How Some Measurements Were Named

Can You Fathom a Bushel and a Peck? Fathom is derived from the Old English word faeom or the Old Saxon word fathmos, meaning the length of the outstretched arms. It was eventually standardized to the length of two yards. Although international nautical charts have converted to meters, the United States still measures depth with fathoms.

Bushel comes from the old French words boissel and boisseau and is a measure of dry goods equal to about eight gallons (or four pecks). Today, it is most commonly used to measure things by their weight, and that weight varies depending on the commodity measured. Typical goods sold by the bushel and their weights include oats (32lb), corn (56lb), wheat (60lb), and soybeans (60lb).

Peck is likely derived from the Old French, pek or picot, and is also a measure of dry goods or commodities. Some retailers, farmers at markets and roadside stands still sell fruits and vegetables by the peck. A peck is equal to about two gallons.

A cord is traced back to the 1600s when wood was sold in bundles tied with a cord. Today, a cord of firewood must take up 128 cubic feet, traditionally in a stack 8′ x 4′ x 4′. The size of a cord of wood is typically regulated, either by a state or national government.

Knot comes from the word of the same spelling meaning intertwined ropes. To measure speed, a long rope had knots tied regularly, about every 50 feet, and a log tied to the end. The log was dropped into the water and a sandglass upended at the same time to time how many knots per time unit. Eventually, the speed of one knot became standardized at one nautical mile (6076 feet vs. land mile 5,280 feet) per hour.

Mach (pronounced mock) was named after Ernst Mach in 1937. Mach numbers represent the ratio of the speed of an object moving through a fluid, gas, or atmosphere and the local speed of sound. When space shuttles re-entered the atmosphere, they initially traveled at a speed greater than Mach 25.

An inch was originally the width of a man’s thumb at the base of the nail. After 1066, 1 inch was equal to 3 barleycorn, dry and round, placed end to end, lengthwise.

A foot was the length of a human foot. A yard was the distance from the tip of the nose to that of the middle finger on an outstretched arm.

One thousand paces of a Roman Legion was a mile. A furlong was originally the length of one furrow in a common field, a bit over 200 feet long. In the 9th century, it was standardized to be the same as a Roman stadium, one eighth of a Roman mile.