welcome to day 8 aug 26 th, 2009! swbat distinguish between accuracy and precision swbat compute...
TRANSCRIPT
Welcome to Day 8 Aug 26th, 2009!
• SWBAT distinguish between accuracy and precision• SWBAT compute percent error• SWBAT make correct measurements
CatalystCreate a hypothesis, IV, DV, Control group for the following
question…- How does a car’s gas mileage change as the tires
pressure changes?
-- If you have SCIENCE FEE MONEY turn it in-- If you have AGENDA MONEY turn it in
Agenda
• Catalyst (10min)
• Accuracy, precision (10min)
• Bulls-eye activity (15min)
• Measurements (10min)
• Measurement activity (30min)
• Percent error ??
• Exit Ticket (10min)
5 Bonus Points(next week – 1 pt off everyday)
Lab Fee, Safety Contract, Notebook Set-up &
Extra Item
Accuracy, Precision and Percent Error
Accuracy, Precision and % Error
Key Point #1: Accuracy is how close you are to the correct or accepted value of a measurement. - (Ex. - throwing a dart close to the bulls eye)-
Accuracy, Precision and % Error
Key Point #2: Precision is how close a series of measurements are to one another. -REPEATABILITY! (Ex. - throwing a dart and hitting the same spot 3 times in a row)
Accuracy, Precision and % Error
Accuracy/Precision Worksheet
- You will need a ruler and a marker
Accuracy, Precision and % Error
1)What was the range (biggest - smallest) of the values for your three trials?
2) How accurate were your drops? Explain.
3) Were your drops precise? Explain.
Measurement Notes
Key Point #3: Science use International System of Units also known as (SI)
WHY?
UNITS
• Volume uses Liters (L) or (mL)
• Mass uses Grams (g)
• Length uses Meters (m)
• Temperature uses Degrees Celsius (C)
Measurement Skills
Measuring Mass:
(1) Zero Scale
(2) Record Mass
(3)If non-digital Estimate last digitMeasuring Volume:
(1) Note increments on graduated cylinder
(2) Read bottom of meniscus at eye-level
(3) Estimate last digit
Measuring Temperature:
(1) Note increments on thermometer
(2) Estimate last digit
Percent error
• Key Point #3: percent error is a quantitative comparison between your value for a measurement and the true value– Tells you how far off your answer is from the
true value.
Accuracy, Precision and % Error
Percent Error
%E = Vactual – Vmeasured X 100
Vactual
|-------|
Accuracy, Precision and % Error
Percent Error
You may never have a negative answer with % error, just drop the negative!
Accuracy, Precision and % Error
% error:Measuring a string you get 18 cm, but Mr. McKnight tells you the string is actually 20 cm long.
Accuracy, Precision and % Error
% error:
[(20 – 18)/20] x 100
Accuracy, Precision and % Error
% error:
[(20 – 18)/20] x 100 = 10%
Accuracy, Precision and % Error
% error:
Measured: 88 mLActual: 83 mL
Accuracy, Precision and % Error
% error:
6.0%
Accuracy, Precision and % Error
% error:
Measured: 140 gActual: 122 g
Accuracy, Precision and % Error
% error:
14.8%
Accuracy, Precision and % Error
% error:
Measured: 3438 mActual: 4888 m
Accuracy, Precision and % Error
% error:
29.7%
IP
Write down if it is good or bad accuracy and precision
Exit Ticket
If you measure the mass of Mr. McKnight to be 222g, but his actual mass is 92g, what is your percent error?