Transcript Measurements Accuracy and Precision

Unit 1: Measurements,
Accuracy, and Precision Notes
Qual vs. Quant
Key Concept 1
– Qualitative data: deals with descriptions.
– Quantitative data: deals with numbers
– Examples
Room Number: 169429
–What was an example from our Mass
and Change Lab of quantitative data?
–T/F Did the Mass and Change Lab have
any qualitative data?
Units
• Significant Figures: Crash Course
Stop at 3:45
• Système Internationale d'Unités (SI) is an
internationally agreed upon system of
measurements.
• A base unit is a defined unit in a system of
measurement that is based on an object or
event in the physical world, and is
independent of other units.
Units (cont.)
Key Concept 2
Comparing Units of Volume
• Key Concept 3: Volume measures the amount
of space an object takes up, and is a derived SI
unit.
Key Concept 4: The
volume of a cube is
V=length x width x height
Comparing Units of Volume
Key Concept 5: The
volume of a cylinder is
V= πr2 x height
• Key Concept 6: Volume can be measured in
cubic centimeters (cm3) using a ruler or in
milliliters (mL) by using a graduated cylinder.
Quick Activity
Goal: Compare the volume that are calculated
using a rule with those measured using a
graduated cylinder.
mL and
3
cm
How can you minimize error?
Class Data
Cube
cubic centimeters (cm3)
Cylinder
Milliliter (mL)
cubic centimeters (cm3)
Milliliter (mL)
Quick Activity
Goal: Compare the volume that are calculated
using a rule with those measured using a
graduated cylinder.
How are mL and
3
cm related?
Closure Type: Socrative Exit Poll
Volume is not concerned an SI unit. How did
scientist choose to define volume?
Yesterday
• Measurements can be:
– Qualitative
– Quantitative
• SI Units
Today
1. SI Units
2. Important of Units
3. Sig Figs
4. Review Scientific Notation
5. Accuracy vs. Precision
SI Units- Length
• 1792: French established a new system of
weights and measures
1 m = distance from N. pole to equator
ten-million
• Then, in the 1870s: 1 m = distance between
fine lines on Pt-Ir bar
– Accurate copies sent around the world
Time and length linked
SI- Length
• The SI base unit for length is the meter (m).
• A meter is equal to the length of the path
travelled by light in a vacuum during a time
interval of 1⁄299,792,458 of a second.
SI- Mass
• The SI base unit of mass is the kilogram (kg),
about 2.2 pounds
SI- Temperature
• The SI base unit of temperature
is the kelvin (K).
• Zero kelvin is the point where
there is virtually no particle
motion or kinetic energy, also
known as absolute zero.
• Two other temperature scales
are Celsius and Fahrenheit.
Importance of Units
• In 1999 the United States lost
the Mars Climate Orbiter as it
approached Mars.
• The loss of the $125 million
spacecraft was due to scientists
confusing English units and
metric units.
Importance of Units
• The spacecraft team in Colorado used English units
of pounds of force to describe small forces needed
to adjust the spacecraft’s orbit. The data was
shipped via computer, without units, to the NASA’s
Jet Propulsion Lab (JPL) , where the navigation
team was expecting the to receive the data in
metric measure.
Importance of Units
• A train of length 2, weighing 200, travels from
Denver to Santa Fe at 15. How long did the
trip take?
Importance of Units
• This brings up the issue of units. In your math
class, numbers by themselves are fine to work
with, but in science a number without units is
pretty useless.
• NO NAKED NUMBERS
“NO STREAKING”
Importance of Units
“We can only be as accurate as
our weakest measurements”.
Today
1. SI Units
2. Important of Units
3. Sig Figs
4. Review Scientific Notation
5. Accuracy vs. Precision
Significant Figures
• Often, precision is limited by the tools
available.
• Key Concept 7: The significant figures of a number are
those digits that carry meaning contributing to its
precision. When measuring significant figures include all
known digits plus one estimated digit.
Learning Check
What is the length of the wooden stick?
Learning Check
• Record the measurement using significant
figures.
Significant Figures (cont.)
• Rules for significant figures
– Rule 1: Nonzero numbers are always significant.
– Rule 2: Zeros between nonzero numbers are
always significant.
– Rule 3: All final zeros to the right of the decimal
are significant.
– Rule 4: Placeholder zeros are not significant. To
remove placeholder zeros, rewrite the number in
scientific notation.
– Rule 5: Counting numbers and defined constants
have an infinite number of significant figures.
Shoulder Partner Practice SF’s
1. 3
2. 2
3. 3
4. 4
5. 4
6. 4
7. 4
8. 2
9. 3
10. 5
Meter Stick
Quick Demo
I need two groups of three volunteers that can
measure using a meter stick (cm).
Number of
trails
1
2
3
Length of
tape in cm
Length of
tape in cm
Scientific Notation
5.67 x
coefficient
5
10
base
exponent
In order for a number to be in correct scientific notation, the
following conditions must be true:
1. The coefficient must be greater than or equal to 1
and less than 10.
2. The base must be 10.
3. The exponent must show the number of decimal
places that the decimal needs to be moved to
change the number to standard notation.
Scientific Notation (cont.)
• The number of places moved equals the
value of the exponent.
• The exponent is positive when the decimal
moves to the left and negative when the
decimal moves to the right.
800 = 8  102
0.00003430 = 3.430  10–5
Today
1. SI Units
2. Important of Units
3. Sig Figs
4. Scientific Notation
5. Accuracy vs. Precision
Accuracy and Precision
• Key Concept 8: Accuracy refers to how
close a measured value is to an accepted
value.
• Key Concept 9: Precision refers to how close
a series of measurements are to one another.
• Pin the mitten on the kitten
Today
1.
2.
3.
4.
5.
SI Units
Important of Units
Sig Figs
Scientific Notation
Accuracy vs. Precision
You have Unit 1A and Unit 1B
Practice Problem.
Unit 1 Prove It Quiz is 26th or 27th