Unit Outline--Topics

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Unit Outline--Topics

• What is Physics?
• Branches of Science
• Science Terms
• Scientific models
• Measuring and Units
• Powers of Ten and conversions
• Graphing
• Experimental Design
• Science vs. Technology
• Analyzing in Physics

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Objectives
Chapter 1

• List basic SI units and the quantities they
  describe.
• Using prefixes and powers of ten.
• Distinguish between accuracy and precision.
• Taking good measurements
• Use significant figures in measurements and
  calculations.

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INTERNATIONAL SYSTEM OF UNITS (SI units)

• Developed for the sake of
• consistency
• ease of understanding
• sharing data

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BASE SI UNITS (standard units)
Measured quantity
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DERIVED UNITS

• Derived Units Combinations of the 7 base units.
• Examples
• Area (length x width) m x m m2
• Velocity (distance/time) m/s

50 m2
5 meters
10 meters
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Numbers as Measurements
Chapter 1

• In SI, the standard measurement system for
  science, there are seven base units.
• Each base unit describes a single dimension, such
  as length, mass, or time.
• The units of length, mass, and time are the meter
  (m), kilogram (kg), and second (s), respectively.
• Derived units are formed by combining the seven
  base units with multiplication or division. For
  example, speeds are typically expressed in units
  of meters per second (m/s).

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MEASUREMENTS

• Measurements consist of a number and a unit.

• Example

100 meters
the number of units or value
the unit
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Dimensions and Units
Chapter 1

• Measurements of physical quantities must be
  expressed in units that match the dimensions of
  that quantity.
• In addition to having the correct dimension,
  measurements used in calculations should also
  have the same units.

For example, when determining area by multiplying
length and width, be sure the measurements are
expressed in the same units.
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Objectives
Chapter 1

• List basic SI units and the quantities they
  describe.
• Using prefixes and powers of ten.
• Distinguish between accuracy and precision.
• Taking good measurements

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SI Prefixes
Section 2 Measurements in Experiments
Chapter 1

• In SI, units are combined with prefixes that
  symbolize certain powers of 10. The most common
  prefixes and their symbols are shown in the
  table.

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Objectives
Chapter 1

• List basic SI units and the quantities they
  describe.
• Using prefixes and powers of ten.
• Distinguish between accuracy and precision.
• Taking good measurements

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Accuracy and Precision
Section 2 Measurements in Experiments
Chapter 1

• Accuracy is a description of how close a
  measurement is to the correct or accepted value
  of the quantity measured.
• Precision is the degree of exactness of a
  measurement.
• A numeric measure of confidence in a measurement
  or result is known as uncertainty. A lower
  uncertainty indicates greater confidence.

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ACCURACY

• Accuracy is the extent to which a measurement
  approaches the true value.

Actual Time 210 pm
Your Time 205 pm
Your accuracy is off by 5 minutes
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Accuracy and Precision

• Precision is the degree of exactness for a
  measurement.
• It is a property of the instrument used.
• The length of the pencil can be estimated to
  tenths of centimeters.
• Accuracy is how close the measurement is to the
  correct value.

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Errors in Measurement

• Instrument error
• Instrument error is caused by using measurement
  instruments that are flawed in some way.
• Instruments generally have stated accuracies such
  as accurate to within 1.
• Method error
• Method error is caused by poor techniques (see
  picture below).

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- The bulls eye represents the true value.- The
darts represent three separate measurements
these darts show good accuracy
accurate
which paint ball mark is more accurate?
less accurate
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PRECISION

• Precision is the degree of exactness of a
  measurement.

• Based on the scale of the measuring instrument.

Smallest tick marks represent millimeters (mm)
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PRECISION VS. ACCURACY
A
B
C
D

• AGood precision and accuracy
• BSome accuracy and poor precision

• CGood precision and poor accuracy
• DPoor precision and accuracy

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Discussion Question

• When shooting free throws, is it better to be
  precise or accurate?

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• Its better to be accurate.

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Objectives
Chapter 1

• List basic SI units and the quantities they
  describe.
• Using prefixes and powers of ten.
• Distinguish between accuracy and precision.
• Taking good measurements

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Measurements

• Dimension - the kind of physical quantity being
  measured
• Examples length, mass, time, volume, and so on
• Each dimension is measured in specific units.
• meters, kilograms, seconds, liters, and so on
• Derived units are combinations of other units.
• m/s, kg/m3, and many others
• Scientists use the SI system of measurement.

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How to Measure?

• Know how to operate the measuring instrument
• Which unit(s) is represented?
• What does each tick mark represent?
• Are there multiple scales?
• Did you zero out the instrument (if possible)
• Be skilled and patient enough to measure with the
  greatest detail possible

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What do the tick marks represent on a meter stick?

• What unit is represented by the smallest tick
  mark on the meter stick?

m? dm? cm? mm?

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What do the tick marks represent on a meter stick?

• What is the measurement?

In mm? 65 mm In cm? 6.5 cm In dm? .65 dm In
m? 0.065 m?
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Why so many different units of measurement for
the same quantity?

• Consider Mark and Suzy. They want to measure the
  length of a room.
• The quantity they are measuring is distance
  (measured quantity).
• They both measure length in units of feet (the
  length of one foot) This is their measuring
  units.
• One important detail Marks foot is longer than
  Suzys foot.

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Why so many different units of measurement for
the same quantity?

• Mark measures the length of the room. So does
  Suzy. Will they have the same measurement? Why
  or why not? Who will have the longer measurement
  in feet?
• Marks measurement is 18 feet and Suzys is 23
  feet.
• The length of a markfoot is not the same as the
  length of a suzyfoot.
• To compare the two different measurements, one
  unit must be converted into the other so that
  both measurements are proportional.
• Standardizing units means to select either the
  length of Marks or Suzys foot as the accepted
  length of the unit called a foot.