description and measurement ms. pollock 8th grade physical science 2009 - 2010
DESCRIPTION
Estimation 4 Rough measurement 4 using something familiar to guess size of new object 4 based on previous experience –chefs –firefightersTRANSCRIPT
Description and Measurement
Ms. Pollock8th Grade Physical Science
2009 - 2010
Measurement
Way to describe world using numbers
how much, how long, how far
more reliable than opinion
describes events– Olympics
Estimation
Rough measurement using something
familiar to guess size of new object
based on previous experience– chefs– firefighters
Estimation
Use “about” check for reasonable
answers– doorknobs about 1 m
from floor– sack of flour about 2
kg– walk about 5 km/h
Precision and Accuracy
Precision: how close measurements are to each other
same every time also number of decimal
places possible with particular tool
degrees of precision
Precision and Accuracy
Accuracy: comparison of measurement to real, actual, or accepted value
How close you are to the desired value
Precision and Accuracy
Important to medical procedures– Stereotactic
Radiotherapy (SRT)– treatment of brain
cancer without damaging healthy cells
Rounding a Measurement Some instruments not capable of great precision rounding rules important for estimation
– digit to right of digit being rounded is 0, 1, 2, 3, or 4: number remains same
– digit to right of digit being rounded is 5, 6, 7, 8, or 9: number increases by one
– digits to right of digit being rounded are right of decimal: delete them
– digits to left of digit being rounded are left of decimal: change to zeros
Rounding a Measurement
Length of sidewalk 135.841 m rounded to tenths place
– 135.8 m– digit to right of tenths place (number 8) was 4
rounded to ones place– 136 m– digit to right of ones place (number 5) was 8
Precision and Number of Digits
Rounding necessary when numbers do not divide evenly
digits that reflect precision significant– digits other than zero– final zeros after decimal point (6.545 600 g)– zeros between other digits (507.0301 g)– initial zeros NOT significant (0.000 2030 g)– zeros in whole number possibly significant (1650)– numbers counted, rather than measured
Applying Math: Rounding
The mass of one object is 6.941 g. The mass of a second object is 20.180 g. You need to know these values only to the nearest whole number to solve a problem. What are the rounded values?
6.941 g (number to right of ones place = 9)– 7 (rounded up)
20.180 g (number to right of ones place = 1)– 20 (remained same)
Following the Rules
Rules for determining significant figures in calculations– multiplication and division
• determined by number with fewer digits• 6.14 X 5.6 = 34.384• 3 2 2
– addition and subtraction• least precise place value• 6.14 + 5.6 = 11.74• 100s 10s 10s