welcome to day 8 aug 26 th , 2009!

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?