1. Chapter One Serway and Jewett
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 true measurement
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, has 7 significant digits.
There are rules for propagating significant digits:
= 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