MEASUREMENT

 Which of the following are measurements?  300lbs  80 marbles  6mL  45km/h  30 degrees Celsius  5ft 6in  16 fingers  5 acres of land

Measurement  Measurement – quantity that has both a number and a unit  Scientific notation – a number written as the product of two numbers. Can you guess the following famous numbers?  3.0 x 10 8 m/s Speed of light  4×10 7 m Earth’s circumference

Scientific Notation  Write these numbers in scientific notation:     90  Write these in long form:  5.6 x 10 2  9.99 x  1 x

Accuracy and Precision  Accuracy: measure of how close a measurement comes to the actual value  Precision: how close a series of measurements are to one another  ***Can have one without the other!  Eg dart board

Accuracy and Precision  C, 76  C, 75  C  C, 78  C, 78  C  C, 81  C, 82  C Which of these is the most precise?  Set 2, measurements closest together. Which is the most accurate?  We would need to know the accepted value.

Error in measurements  Error = experimental value – accepted value  Experimental value – the measurement in the lab  Accepted value – the correct value.  Error can be positive or negative.  If the boiling point of water measure in the lab is 99.1  C, what is the error?  Percent error = ___  error  _ x 100% accepted value  What is the percent error in the above question?

Significant Figures  Significant figures – include all the digits that are known and one last digit that is unknown.  If you went to Walmart and the mangoes you were going to buy weighed 2.64lbs which digits are known and unknown?  Sig figs are important because sometimes the number or calculation can be greatly affected by the number of significant figures in the values used.

 Read pg. 66/67 Rules for determining whether a digit in a measured value is significant. What are the 6 rules?

Rules for determining if a digit in a measured value is significant 1. Every non-zero digit is significant. 2. Zeros between non-zeros are significant. 3. Left-side zeros are placeholders. Eg Zeros to the right of the decimal and at the end of a number are significant. Eg Zeros at the rightmost end of a measurement before a decimal point can be placeholders or significant. Eg. 300 (not significant) and 3.00 x 10 2 (significant). 6. There are 2 situations when there can be an unlimited number of sig figs. 1 – when you count. 2 – defined quantities like 1min = 60 seconds.

Pg. 72 q’s 10, 11, 13, 14

 Read pgs 68-71