Physics Chapter One Serway and Jewett Chapter One

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Physics Chapter One Serway and Jewett

Physics Chapter One Serway and Jewett

Chapter One • What is a physics measurement? It is a combination of •

Chapter One • What is a physics measurement? It is a combination of • 1) Magnitude • 2) Units (almost always) • 3) Uncertainty (or Significant Digits) • 4) Direction (for vectors)

Magnitude • Magnitude is the quantitative part of any measurement; it itself has no

Magnitude • Magnitude is the quantitative part of any measurement; it itself has no units included and generally needs some combination of uncertainty, units, and direction to fulfill the requirements of a true measurement • i. e. for the example: Velocity = 14 ± 2 m/s NW The magnitude of this measurement is 14.

Units • Units are based on the SI version of the metric system. •

Units • Units are based on the SI version of the metric system. • The base units for mechanics are: m, kg, s. • Other units can be built out of combinations of these • Prefices are used to denote orders of magnitude: Em Pm Tm Gm Mm km m mm μm nm pm fm am

Uncertainty is part of any real physical measurement: Length = 16 meters ± 2

Uncertainty is part of any real physical measurement: Length = 16 meters ± 2 meters There is a formal method for dealing with uncertainties in formulae which we will use in next week’s lab

Significant Digits Significant digits are a “shorthand” for the uncertainty implicit in a physical

Significant Digits Significant digits are a “shorthand” for the uncertainty implicit in a physical measurement: the last significant digit is approximately equal to the uncertainty. L = 14. 6 m is approximately L = 14. 6 m ± 0. 1 m You should never have more significant digits in the solution than you did to start with. 3 significant digits is almost always enough.

Significant Digits Continued 10 and 10, 000 both have one significant digit. 10. 0

Significant Digits Continued 10 and 10, 000 both have one significant digit. 10. 0 has 3 significant digits. 10, 000. 00 has 7 significant digits. There are rules for propagating significant digits: 1 + 1. 0 = 2 not 2. 0 since 1 is one significant digit while 1. 0 has two significant digits. The smallest number of significant figures always dominates. • •

Direction • All vector quantities have a direction as well as magnitude, uncertainties and

Direction • All vector quantities have a direction as well as magnitude, uncertainties and units • May be expressed in (x, y, z) cartesian coordinates – (i. e. N, W, E, S, up, down) • May also be expressed in spherical or cylindrical coordinates (i. e. latitude, longitude, elevation) • We will use both 2 -d and 3 -d vectors