Chapter One: Basic Physics Concepts PDF

Chapter one Basic concepts Introduction: - The goal of physics is to provide an understanding of the physical world by developing theories based on experiments. A physical theory is essentially a guess, usually expressed mathematically, about how a given physical system works The theory...

Chapter one Basic concepts Introduction: - The goal of physics is to provide an understanding of the physical world by developing theories based on experiments. A physical theory is essentially a guess, usually expressed mathematically, about how a given physical system works The theory makes certain predictions about the physical system which can then be checked by observations and experiments  If the predictions turn out to correspond closely to what is actually observed, then the theory stands, although it remains provisional. No theory to date has given a complete description of all physical phenomena, even within a given sub discipline of physics. Every theory is a work in progress. The Metric system (m.k.s) In this system the Length is measured in meters, the Mass is measured in kilograms, and the time is measured in seconds. The Centi-metric system (c.g.s) In this system the Length is measured in centimeters, the Mass is measured in grams, and the time is measured in seconds. SI Base Units Quantity Unit Name Unit abbreviation Length meter m mass kilogram kg time second s Temperature Kelvin K Amount of mole mol substance Electric current Ampere A Luminous candela cd Intensity Derived Units: These quantities depend on the basic (fundamental) quantities; they are defined according to their relationships with the basic quantities. Some examples of derived quantities: -Area: is length × length Units: m2, cm2, km2….  -Volume: it is the space occupied by a body. Volume= length × length × length Units: m3, cm3, km3…. -Density: is the mass per unit volume. It is denoted by(ρ) ρ =M/V units: kg/m3, g/cm3  -Speed: is the rate of change of distance with time. Speed=distance/time Units: meter/second, kilometre/second, mile/hour -Acceleration: is the rate of change of speed with time: Acceleration=speed/time Units: m/s.s = m/s2 , km/s2 , km/h2 ,…….  Class work:- Obtain the unit of N N=1/2 k z2 Where :- N≡ Energy K≡ mass z≡ speed Some Prefixes for Powers of ten Used with “Metric”(SI and cgs) Units Power Prefix Abbreviation 10-15 femto F 10-12 pico P 10-9 nano N 10-6 micro µ 10-3 milli M 10-2 centi C 10-1 deci D 101 deca Da 103 kilo K 106 mega M 109 giga G 1012 tera T 1015 peta P SI writing style Symbols are written in lower case, except for symbols derived from the name of a person. For example, the unit of pressure is named after Blaise Pascal, so its symbol is written "Pa" whereas the unit itself is written "Pascal".  A space should separate the number and the symbol, e.g. "2.21 kg", "7.3×102 m2", "22 °C". Exceptions are the symbols for plane angular degrees, minutes and seconds (°, ′ and ″), which are placed immediately after the number with no intervening space.  Spaces may be used to group decimal digits in threes, e.g. 1 000 000 or 342 142 (in contrast to the commas or dots used in other systems, e.g. 1,000,000 or 1.000.000). This is presumably to reduce confusion because a comma is used as a decimal in some countries (such as France). In print, the space used for this purpose is typically narrower than that between words