It is defined to be the mass of a platinum-iridium cylinder, housed at the International Bureau of Weights and Measures near Paris. The SI unit for mass is the kilogram (kg). Distance traveled is speed multiplied by time. These are called derived units.įigure 1.14 The meter is defined to be the distance light travels in 1/299,792,458 of a second through a vacuum. All other units are made by mathematically combining the fundamental units. The units in which they are measured are the meter, kilogram, second, ampere, kelvin, mole, and candela ( Table 1.1). In this course, we will mainly use five of these: length, mass, time, electric current and temperature. Units for other physical quantities (such as force, speed, and electric charge) described by mathematically combining these seven base units. In physics, there are seven fundamental physical quantities that are measured in base or physical fundamental units: length, mass, time, electric current temperature, amount of substance, and luminous intensity. Some physical quantities are more fundamental than others. Virtually every other country in the world now uses the metric system, which is the standard system agreed upon by scientists and mathematicians. Today, the United States is the only country that still uses English units extensively. English units were historically used in nations once ruled by the British Empire. There are two major systems of units used in the world: SI units (acronym for the French Le Système International d’Unités, also known as the metric system), and English units (also known as the imperial system).
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