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Physics

Physics. Chapter One Serway and Jewett. 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.

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Physics

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  1. Physics Chapter One Serway and Jewett

  2. 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)

  3. 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 truemeasurement • i.e. for the example: Velocity = 14 ± 2 m/s NW The magnitude of this measurement is 14.

  4. 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

  5. Uncertainty 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 this week’s lab

  6. 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.

  7. 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.

  8. 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

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