Lecture2

# Lecture2 - Physics 2A Lecture 2: Jan 9, 2008 Vivek Sharma...

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Physics 2A Lecture 2: Jan 9, 2008 Vivek Sharma UCSD Physics

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Reading Assignments For This Week Self-Study “How to Succeed in Physics by Really Trying”, & Using Your Textbook” & Chapter 1 : Sections 1.1-1.6 Second Quiz on Tuesday 15th, Covers Ch 1 Start reading NOW !
Today : Start Gathering Tools • Nature of Physics • Idealized Models • Standard & Units • Measurement Error • Order of magnitude • Significant figures • Scalars & Vectors

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Nature of Physics • Physics is experiment driven science • Observe phenomena , find patterns & principles (physical theory) that relate and explain diverse observed phenomena • Every physical theory has a range of validity outside which it is not applicable Æ CM
Models in Physics • Model is a simplified version of a physical system that would be too complicated to analyze in full detail • In a model, we overlook the minor effects to concentrate on the most important feature of the system it describes, e.g. analyzing motion of a baseball thrown in air • The predictions based on a model are only as good as the features present in the model • Will use models of phenomena throughout the course to learn about its essential features

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An Example of Idealization/Modeling
Unit of Physical Quantities • Physics is an experimental science, experiments require measurements • A number used to describe a physical phenomenon quantitatively are called physical quantities . e.g. your height and weight • When measuring a quantity, we compare it with some reference standard. Such a standard defines a unit of the quantity – e.g: SI Units – units of measurements must be calibrated: exactly the same in all parts of the universe ! Kilogram (kg) Second (s) Meter (m) Mass Time Length

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Describing Physical Quantities •Sca la r s Æ Quantities such as time, temperature, mass, speed can be described by just one number with an appropriate unit –math is simple: 2kg +3kg = 5kg (always!) • Vectors Æ Quantities with direction associated with them such as those quantifying motion (displacement, velocity) –needs a magnitude (how large or small) –needs a pointing direction (which way?) –math for these objects is more complicated
• Describes net change in position of an object • An example of a displacement vector • Example of same displacement vector but with a different path • Apologies to Robert Frost, both paths taken arrive at the same point same magnitude, directions, although paths very different The Displacement Vector V V

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The Zero Vector
Equal, Parallel & Anti Parallel Vectors

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## This note was uploaded on 08/23/2008 for the course PHYS 2A taught by Professor Hicks during the Winter '07 term at UCSD.

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Lecture2 - Physics 2A Lecture 2: Jan 9, 2008 Vivek Sharma...

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