Lecture02

# Lecture02 - PHYSICS 149: Lecture 2 Chapter 1 1.1 Why study...

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PHYSICS 149: Lecture 2 • Chapter 1 – 1.1 Why study physics? – 1.2 Talking physics – 1.3 The Use of Mathematics – 1.4 Scientific Notation and Significant Figures – 1.5 Units – 1.6 Dimensional Analysis – 1.7 Problem-Solving Techniques – 1.8 Approximation – 1.9 Graphs (self study) Lecture 2 Purdue University, Physics 149 1

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Equations Understand the concepts first! • Equations allow us to use the concepts to make predictions quantitatively. • Physicists perform experiments to verify predictions. • Units are an essential part of each value in equations and must be handled using dimensional analysis techniques. • Vector equations relate direction as well as magnitude. You will learn about vectors in this course. – The car moved 2 miles – The car moved 2 miles west provides more information West Lecture 2 Purdue University, Physics 149 2
Significant Figures The result of a calculation indicates the precision of the measurement with the significant figures. The number of significant figures in a measurement, such as 2.531 g, is equal to the number of digits that are known with some degree of confidence (2, 5, and 3) plus the last digit (1), which is an estimate or approximation. – Postage Scale 3 (1 g) 1 significant figure – Two-pan balance 2.53 (0.01 g) 3 significant figures – Analytical balance 2.531 (0.001 g) 4 significant figures Zeros within a number are always significant. Both 4308 and 40.05 contain four significant figures. Zeros that do nothing but set the decimal point are not significant. Thus, 470,000 has two significant figures. Trailing zeros that aren't needed to hold the decimal point are significant. For example, 4.00 has three significant figures. Lecture 2 Purdue University, Physics 149 3

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Significant Figures • Significant figures tell the precision of a measurement. – 12 g is not the same as 12.0 g in terms of precision. • 12 g implies a value more than 11 and less than 13. • 12.0 g tells you the value is between 11.9 and 12.1 • All non-zero digits are always significant: – 1.23 12.3 123 all have 3 sig. figs Leading zeros are never significant: – 0.0013 = 2 sig. figs 0.14 = 2 sig. figs • Trapped zeros are always significant: – 1.002 = 4 sig. fig • Trailing zeros are significant if they are after a decimal point and if they are after a non-zero digit: – 12.00 = 4 sig. fig – 0.00120 = 3 sig. fig (the first three zeros are leading ) Lecture 2 Purdue University, Physics 149 4
ILQ 1-1 (unofficial) State the number of significant figures in 0.005800 cm: a) 7 b) 4 c) 5 d) 2 Lecture 1 Purdue University, Physics 149 5

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Prefixes (the Power of 10) • The value of a quantity can be too large or too small in a unit. It is very convenient to use a prefix in front of the unit.
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## This note was uploaded on 04/23/2011 for the course PHYS 149 taught by Professor Staff during the Spring '08 term at Purdue University.

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Lecture02 - PHYSICS 149: Lecture 2 Chapter 1 1.1 Why study...

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