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 PRECISION like  0.02 or   0.05

Accuracy and Precision Which data set is more precise? Why? TrialMeasurement Avg TrialMeasurement Avg100.00

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 kilo hecta deka deci centi milli kmkm cmcm m l dldl mlml kgkg mgmg msms g s m

Converting Metrics REMEMBER 10!!! Metric units are based on the powers of ten

Converting Metrics

Ya Gotta Know 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

Converting 53 centimeters = ??? meters 53 cm X = m

Converting 53 centimeters = ??? meters 53 cm X m cm = m

Converting 53 centimeters = ??? meters 53 cm X 1 m cm = m

Converting 53 centimeters = ??? meters 53 cm X 1 m cm = 0.53 m

Conversion Factor 53 centimeters = ??? meters 53 cm X 1 m cm = 0.53 m What I want What I have X X

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 m = mm What I want What I have

27 meters = ??? millimeters 27 m X 1000 mm m = 27,000 mm What I want What I have X X

??? seconds = 450 milliseconds 450 ms X = 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 ms = s What I want What I have

??? seconds = 450 milliseconds 450 ms X 1 s ms = s What I want What I have

0.087 kilometers = ??? centimeters km X cm km = cm

0.087 kilometers = ??? centimeters km X m km = m = cm cm m X m

0.087 kilometers = ??? centimeters km X = 87 m = 8,700 cm 100 cm m X 87 m 1000 m km