The SI unit for period is the second. For counts per unit of time, the SI unit for frequency is hertz (Hz), named after the German physicist Heinrich Hertz; 1 Hz means that an event repeats once per second.A previous name for this unit was cycles per second (cps).or each dot, f is the frequency in hertz (Hz) â meaning the number of times per second (i.e. cycles per second) that it flashes â while T is the flashes' period in seconds (s), meaning the number of seconds per cycle. Each T and f are reciprocal.
Photo: CertainTeed. Economical to produce, relatively easy to install and widely available, asphalt shingles are todayâs most popular roofing materialânot only because theyâre less costly than wood, wood shakes, tile, metal or slate, but also because their guaranteed life span pits them favorably against competitors.
The word âmetalâ covers a lot of ground when it comes to metal roofing materials. Steel, stainless steel, aluminum, copper, and zinc alloys are all materials used for metal roofing. Each has different properties that affect durability, price, and appearance. Conventional Metal Roofing Materials. By far, the most common materials used for metal roofs are steel and aluminum. Steel, used for most metal roofing, is heavier and sturdier than aluminum. Manufacturers have settled on a number of durable coatings and finishes that protect steel from rust and corrosion.