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Ch. 1, Physics & Measurement. Outline. What is physics? Subareas of physics Why study physics? Physics and Measurements: Nature of measurements in physics Units of measurements Conversion of units Dimensional analysis. Introduction. What is physics?.
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Outline • What is physics? • Subareas of physics • Why study physics? • Physics and Measurements: • Nature of measurements in physics • Units of measurements • Conversion of units • Dimensional analysis
What is physics? • Physics:The most basic of all sciences! • Physics: The “Mother” of all sciences! • Physics= The study of the behavior of and the structure of matter and energy and of the interaction between matter and energy.
Physics: • Goal of Physics (& all of science): To quantitatively and qualitatively describe the “world around us”. • PhysicsIS NOT merely a collection of facts and formulas! • PhysicsIS a creative activity! • Physics Observation Explanation. • Requires IMAGINATION!!
Sub Areas of Physics • Physics of 16th & 17th Centuries: • Motion (MECHANICS) • Fluids & Waves • Physics of 18th & 19th Centuries: • Electricity & magnetism • Light & optics • Physics of the 20th Century! : • Relativity, atomic structure, condensed matter, nuclear physics, …. • These are the most interesting & the most relevant to modern technology!
Why study physics?Physics & its relation to other fields • The “Mother” of all Sciences! • The foundation for and is connected to ALL branches of science and engineering. • Also useful in everyday life and in MANY professions • Chemistry • Life Sciences • Architecture • Engineering. • ….
Model, Theory, Law • Model: An analogy of a physical phenomenon to something we are familiar with. • Theory: More detailed than a model. Puts the model into mathematical language. • Law: Concise & general statement about how nature behaves. Must be verified by many, many experiments! Only a few laws. • Not comparable to laws of government!
Measurements • Goal of Physics (& all of science): To quantitatively and qualitatively describe the “world around us”. • Measurements Used to describe natural phenomena • Needs defined standards
Units, and Standards • All measured physical quantities have units. • Units are VITAL in physics!! • Standards for UNITS • Readily accessible • Possess some property that can be measured Reliably • Must yield the same results when used by anyone anywhere • Cannot change with time
Standards of FundamentalQuantities Standardized systems • Agreed upon by some authority, usually a governmental body • In 1960 an international committee agreed upon SI: Systéme International
SI System • Most of the modern world, except the USA! use (almost) exclusively the SI system of units. SI = “Systéme International” (French) More commonly called the “MKS system” (meter-kilogram-second) or more simply, “the metric system”
Fundamental Quantities and Their Units: • Length Meter • Mass kilogram • Time second • Temperature Kelvin • Electric Current Ampere • Luminous Intensity Candela • Amount of Substance mole
SI or MKS System • Defined in terms of standards for length, mass, and time. • Length unit: Meter (m) (kilometer = km = 1000 m) • Standard meter. Newest definition in terms of speed of light Length of path traveled by light in vacuum in (1/299,792,458) of a second! • Mass unit: Kilogram (kg) • Standard kilogram. Defined in terms of a kilogram, based on a specific cylinder kept at the International Bureau of Standards
DENSITY • A property of any substance is its density (Greek letter rho), defined as the amount of mass contained in a unit volume, which we usually express as mass per unit volume:
SI or MKS System • Time unit: Second (s) • Standard second. Newest definition time required for 9,192,631,770 oscillations of radiation emitted by cesium atoms!
The primary frequency standard (an atomic clock) at the NIST. This device keeps time with an accuracy of about 3 millionths of a second per year.
Other Systems of Units • CGS(centimeter-gram-second) system • Centimeter = 0.01 meter • Gram = 0.001 kilogram • British(foot-pound-second) system • Only used by USA and some third world countries. • Rest of world (including Britain!) uses SI system. • Conversions exist between the British & SI
Basic & Derived Quantities • Basic Quantity Must be defined in terms of a standard (meter, kilogram, second). • Derived Quantity Defined in terms of combinations of basic quantities • Unit of speed = meter/second = m/s
Units and Equations • In dealing with equations, remember that the units must be the same on both sides of an equation (otherwise, it is not an equation)! • Example: You go 90 km/hr for 40 minutes. How far did you go? • Equation from Ch. 2: x = vt, v = 90 km/hr, t = 40 min. To use this equation, first convert t to hours: t = (⅔)hr so,x = (90 km/hr) [(⅔)hr] = 60 km The hour unit (hr) has (literally) cancelled out in the numerator & denominator!
Dimensional Analysis • Well help minimize the need for rote memorization of equations. • Dimensional analysis makes use of the fact that: Dimensions can be treated as algebraic quantities. • That is, quantities can be added or subtracted only if they have the same dimensions. • Furthermore, the terms of both sides of an equation must have the same dimensions.
