Unit 1 – Introduction to Physics

 Physical quantitiesmassforce  CurrentunitSI units  International systemkilogramsecond  Basic quantitiesmeterampere  Derived quantitiesKelvinmole  Candelascaleperiods  Avogadro’s numbertriple point  Absolute temperature scaleblack body

 Physical quantities are things such as mass, force, and current, which can be quantified by measurement.  All physical quantities have to be measured in some way and each therefore has its own unit.  Units are chosen by international agreement and are called SI units abbreviated from the French (Systeme International d’Unite).

 All quantities are classified as either basic quantities or derived quantities.  Basic quantities are a set of quantities from which all other quantities can be defined.  Each basic quantity has its basic SI unit, in terms of which any other SI can be defined. Insert basic quantity table

 Basic SI Units  Kilogram (kg) is the SI unit of mass. It is equal to the mass of a platinum iridium cylinder kept at Sevres, near Paris.  Second (s) is the SI unit of time. It is equal to the period of a type of radiation emitted by the cesium-133 atom.

 Meter (m) is the SI unit of length. It is equal to the distance light travels in a vacuum in 1/299,792,458 of a second.  Ampere (A) is the SI unit of electric current. It is equal to the size of a current flowing through wires in a vacuum, that produces a force of 2 X N every meter.

 Kelvin (K) is the SI unit of temperature. It is equal to 1/ of the temperature of the triple point of water on the absolute temperature scale.  Mole (mol) is the SI unit of the quantity of a substance. It is equal to the amount of substance which contains X particles. (Avogadro’s number)

 Candela (cd) is the SI unit of intensity of light. It is equal to the strength of light from 1/600,000 m 2 of a black body at the temperature of freezing platinum and at a pressure of 101,325 N/m 2.  A black body is a hypothetical object which absorbs all radiation that falls on it, and is also the best radiator (heat energy emitter).

 Prefixes  A given SI unit may sometimes be too large or small for convenience.  Example: The meter is too large for measuring the thickness of a piece of paper.

 Prefixes  Standard fractions and multiples of the SI units are therefore used and written by placing a prefix before the unit.  Example: 1 millimeter (mm) is equal to 1/1000 of a meter.  Thickness of a sheet of paper is 0.1 mm which equals.0001 m or 1/10,000 of a meter. Insert Fractions and multiples table

 Derived quantities are quantities other than basic quantities.  Derived quantities have derived SI units which are defined in terms of the basic SI units or other derived units.  They are determined from the defining equation for the quantity and are sometimes given special names. Insert derived quantity table