Measurementbook reference p. 51 -62

• Accuracy The accuracy of the measurement refers to how close the measured value is to the true or accepted value.

For example, if you used a balance to find the mass of a known standard 100.00 g mass, and you got a reading of 78.55 g, your measurement would not be very accurate.

• Precision

Precision refers to how close together a group of measurements actually are to each other.

Accuracy and precision examples

• Precise accurate and precise

Errors

• Accuracy with error & precision with error

Significant figuressig fig (sf)

• Rules for reporting meaningful experimental results.

• Prevents propagation of error.

Sig figs

• Any non-zero number is significant• Zeros between sig figs are significant• Zeros in front of all nonzero digits are not significant

• Zeros at the end of number and to right of the decimal point are significant

• Zeros to the left of the decimal are tough. If they were measured they are significant. Use scientific notation.

Sig fig examples

• 24.7 g • 0.346 g• 2005 m• 3.509 ml• 0.00067 g• 56.00• 6.010• 600• 720

• 3 sf• 3 sf• 4 sf• 4 sf• 2 sf• 4 sf• 4 sf• 1 or 3 6.00 x 102

• 2 or 3 7.20 x 102

Calculations and sig figAddition subtraction

• An answer can not be more precise than the least precise measurement

• 4.34 cm - 2.3 cm = 2.04 so 2.0 cm• Rounding rules if the digit after the last significant digit is 5 or greater round up

• 10.345 g + 2.3 g = 12.645 so 12.6 g

Calculations and sig figmultiplication division

• The LEAST MOST rule - the most sig fig reported in your answer comes from the least number of sig fig in the calculation

• 3.4 cm x 5.43 cm = 18.462 so 18 cm

• 18.45 g /3.45 g = 5.347826087 so 5.35