Chapter 2 Measurement

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Chapter 2Measurement
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Section 1Description and Measurement

• Every day we make observations. Sometimes those
  observations require that we take measurements of
  things.
• Observations can be inaccurate.
• Making measurements removes much of the doubt
  about an observation.

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• Measurement describes the world using numbers.
• -Types of measurements might include distance,
  time, speed, volume, and mass.
• -Measurements can also help to describe
  events.

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• However, you must choose the proper instrument
  when you measure something. You must consider
  what it measures and how precise it is.
• For example What instrument would you use to
  determine the winner at a swim meet? _________
• How precise should that instrument be?

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Description and Measurement

• Some measurements can be exact, but others are
  too difficult to measure exactly. In those cases
  we make approximate measurements.
• When do you think you should make an approximate
  measurement?
• On what do you base that measurement?

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• Approximated measurement based on previous
  experience is estimation.
• Estimation is useful when actual measurements are
  not easily made.
• Estimation can check that an answer is
  reasonable.
• When you estimate, you often use the word about.

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Description and Measurement

• Precision and Accuracy
• Precision - a description of how close
  measurements are to each other.
• Used to discuss a number of decimal places a
  measuring device can measure.
• Degrees of Precision todays measuring devices
  are more precise.

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• Accuracy a comparison of a measurement to the
  actual value.
• Precision and accuracy are important in many
  medical procedures.
• Measurements can be rounded when precision is not
  needed.

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• When should you not estimate a value?
• Look at the photo in Figure 3 on page 40 of your
  textbook. Estimate the height of the tree.
• Using Figure 4 on page 41 of your textbook, which
  of the three timepieces would you use to be sure
  to make it to school on time?

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• What is the difference between precision and
  accuracy?
• If you dont have the measuring instrument in
  front of you to determine its precision, how can
  you tell which numbers in the measurement are
  important?

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• Significant digits reflect the true precison of
  a calculation or measurement.
• Rules for determining significant digits
• All non-zero digits are significant.
• Any zero between non-zero digits are significant.
• Any zero to the right of the decimal point AND to
  the right of a non-zero digit is significant.

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• How many significant digits are in each of the
  following numbers?
• 53.27 5. 20.009
• 600 6. 93.10
• 0.0123 7. 100.01
• 804 8. 54.0020

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• Answers should always be recorded in a specific
  number of significant digits.
• In multiplication or division the measurement
  with the fewest significant digits determines the
  number of significant digits in the answer.
• Example 23.056 x 21 484.176,
• but following the above rule, the answer becomes
  480.

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• In addition or subtraction the number of
  significant digits in the answer is determined to
  the place value of the least precise measurement.
• Example 23.7 34.65 83.041
• 141.391
• but following the above rule, the a answer
  becomes 141.4

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Section 2 SI Units

• A common system of measurement is very important.
• In ancient times measurements were based upon the
  physical characteristics of the pharaoh.
• Why would this system of measurement be a
  problem?

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• We need to be able to accurately communicate
  measurements for science, business, and industry.
• The system that is used for this accurate
  communication is the International System. This
  system, SI, has units based upon multiples of
  ten.
• These units are very specific units of another
  system called the metric system.
• (Look at Table 1 on page 46 of your textbooks.)

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• The metric system is a measuring system based on
  multiples of ten.
• It uses a set of pre-fixes based on multiples of
  ten to change the meaning of the measurement.
• (Look at Table 2 on page 46 of your textbooks.)

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• Measuring Length
• Length is the distance between two points. In SI
  units it is measured in meters.
• One meter is about the length of a baseball bat
  or slightly longer than a yard.

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• Not every length measurement should be made in
  meters.
• The length of your pencil might be better
  measured in centimeters.

The distance from New York to Chicago would be
measured in kilometers.
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• Measuring Volume
• Volume is the amount of space an object takes up.
  In SI units, volume is measured in cubic meters.
• Just as with length, you must choose the most
  appropriate measurement for the object you are
  measuring. You would not use cubic meters to
  determine the volume of tea cup.
• How many cubic centimeters are in a cubic meter?

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• To find the volume of a regular shape measure
  the length, width, and height of the object then
  multiply those measurements together.

For example To find the volume of a wooden
block, you would have to measure its length (25
cm), its width (32 cm), and its height (15 cm).

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• The volume is then determined by multiplying
  those three measurements
• 25 cm x 32 cm x 15 cm
• 12,000 cm3

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• To find the volume of an irregularly shaped
  object you must use a method other than directly
  measuring the sides of the object.
• The method to use in this situation is volume by
  immersion.
• This means you will place the object in a liquid
  (such as water) and determine how much water it
  displaces.
• That will be its volume!

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• Mass
• The amount of matter in an object is its mass.
• In SI units, mass is measured in kilograms.

• Weight is a measurement of force.
• In SI units, weight is measured in newtons.

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• Weight and mass do not measure the same thing!
• Mass measures how much stuff (matter) is in an
  object and will not change unless we take away or
  add to the object.
• Suppose you travel to the moon.
• Will your mass change?

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• Weight is determined by the pull of gravity.
• Your weight might change if the pull of gravity
  changes.
• On the moon, will you weigh more, less, or the
  same as on Earth?

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• Temperature is a measure of the kinetic energy in
  the particles of matter.
• The SI unit of temperature is the kelvin.

Time is the interval between two events. The SI
unit of time is the second.
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• Rate is the amount of change of one measurement
  in a given amount of time.
• Rate can be measured in units of
• m/sec,
• baseballs/minute,
• gallons/hour,
• hamburgers served/hour, etc.

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Section 3Drawings, Tables, and Graphs

• Scientific illustrations often make information
  more clear than written text can.
• Drawings can emphasize only necessary details or
  show things you cant see.
• Photographs show an object exactly as it is at a
  single moment.

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• Tables display information in rows and columns
  for easier comprehension.

Trial Distance (m) Time (s)
1
2
3
4
5
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• Graphs collect, organize, and summarize data
  visually.

• Line graphs shows the relationship between
  variables, which must be numbers.
• Bar graphs use bars of different sizes to show
  relationships between variables one variable is
  divided into parts the other variable is a
  number.
• Circle graphs show parts of a whole as
  percentages.
• Scales on graphs must be carefully constructed
  and analyzed so users easily understand the
  information.

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• Dont forget
• Measuring is a very important part of science
  it is exact and leaves no doubt in a quantity.
• In order to communicate properly, people must use
  a common system of measurement.
• We use drawings, tables, and graphs to
  communicate our ideas in forms that make the data
  easier to understand.

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Chapter 2Measurement

• The End