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Accuracy, Precision, Estimation, Measurements!!!
9/14/09
•
Accuracy
• The degree of closeness of a measured or calculated quantity to its actual (true) value.
Precision
• Also called reproducibility or repeatability, the degree to which further measurements or calculations show the same or similar results.
Accuracy and Precision
• Instruments have a defined PRECISIONlike 0.02 or 0.05
109.80 0.05
Accuracy and Precision
• Which data set is more precise? Why?
Trial Measurement
1 100.01
2 100.01
3 99.98
4 100.00
Avg 100.00
Trial Measurement
1 100.10
2 100.00
3 99.88
4 100.02
Avg 100.00
Estimation
• The calculated approximation of a result which is usable even if input data may be incomplete or uncertain.
• Common Estimates: – Meter– Centimeter– Millimeter
Estimation
• Use of estimates– Allows you to confirm correct units are being
used– Allows you to confirm that you have reached a
reasonable answer– Allows you to determine distance or length
without taking actual measurements– Allows you to understand/interpret distances or
lengths
Measurements
• Main Scientific Units (Si units)– Length – Meters (m)– Volume – Liters (L)– Time – Seconds (s)– Mass – Grams (g)– Force – Newtons (N)
Remember your Sig Figs!
• Significant Figures (Significant Digits) - the digits of a number that carry meaning contributing to its precision
• Using Sig Figs. How long is this paperclip?
Remember your Sig Figs!
• How long is this paperclip?
• Are you sure?
Remember your Sig Figs!
• How long is this paperclip?
• Are you sure?
Remember your Sig Figs!
• How long is this paperclip?
• Are you sure?
Remember your Sig Figs!
• How long is this paperclip?
• Are you sure?
Remember your Sig Figs
• Recording Sig Figs– Always write the number of digits you KNOW
plus ONE guess– Remember your units!!!
Remember your Sig Figs
• Reading Sig Figs– Remember, the last number is the guess. So the
more digits, the more precise the measurement was!
– Pacific Atlantic Rule
Remember your Sig Figs
• Using the Pacific-Atlantic Rule!• If decimal point is Present start on the
Pacific side. If decimal point is Absent, start on the Atlantic Side.
• Start counting at the first number that isn’t 0 and don’t stop counting!
• The more significant figures present, the more precise the measurement!
Converting Metrics
• First of all, forget the English system. – 1 inch = 2.54 cm– 1 mile = 1.61 km– 2.2 pounds = 1 kg– 33.8 ounces = 1 L– Etc. etc. etc.
meter liter gram second
kilohectadeka
decicentimilli
km
cm
mm
l
dl
ml
kg
mgms g
s
m
Converting Metrics• REMEMBER 10!!!
• Metric units are based on the powers of ten
Converting Metrics
Ya Gotta Know...
1000 meters = 1 kilometer
1 meter = 10 decimeters 1 meter = 100 centimeters 1 meter = 1000 millimeters
Converting
• You can multiply anything by 1 without changing it
• Anything divided by itself is 1
• I can "cancel" common factors when multiplying fractions
Converting53 centimeters = ??? meters
53 cm X
-------------
= m
Converting53 centimeters = ??? meters
53 cm X m
------------- cm
= m
Converting53 centimeters = ??? meters
53 cm X 1 m------------- 100 cm
= m
Converting53 centimeters = ??? meters
53 cm X 1 m------------- 100 cm
= 0.53 m
Conversion Factor53 centimeters = ??? meters
53 cm X 1 m------------- 100 cm
= 0.53 m
What I want-----------------What I have
XXXX
27 meters = ??? millimeters
27 m X -------------= mm
What I want-----------------What I have
27 meters = ??? millimeters
27 m X mm
------------- m
= mm
What I want-----------------What I have
27 meters = ??? millimeters
27 m X 1000 mm------------- 1 m
= mm
What I want-----------------What I have
27 meters = ??? millimeters
27 m X 1000 mm-------------
1 m= 27,000 mm
What I want-----------------What I have
XXXX
??? seconds = 450 milliseconds
450 ms X -------------
= 0.4 50 s
What I want-----------------What I have
??? seconds = 450 milliseconds
450 ms X s
------------- ms= s
What I want-----------------What I have
??? seconds = 450 milliseconds
450 ms X 1 s
-------------1000 ms
= s
What I want-----------------What I have
??? seconds = 450 milliseconds
450 ms X 1 s
-------------1000 ms
= 0.450 s
What I want-----------------What I have
0.087 kilometers = ??? centimeters
0.087 km X cm
------------- km
= cm
0.087 kilometers = ??? centimeters
0.087 km X m
------------- km
= m
= cm cm
------------- m
X m
0.087 kilometers = ??? centimeters
0.087 km X = 87 m
= 8,700 cm100 cm-------------
1 mX87 m
1000 m-------------
1 km
