ERROR! Error = Measured Value – Accepted Value • Science references list the density of aluminum as being 2.7g/cm3. • Suppose you perform an experiment and your results show aluminum having a density of 2.8g/cm3 Aluminum 2.7g/cm3 Aluminum 2.8g/cm3 Error = 2.8g/cm3 – 2.7g/cm3 = 0.1g/cm3 Error can be positive or negative but sometimes it isn’t very useful! Accepted Measured • If you have a 10ft long table (accepted value) and your results state it is 5ft long (measured value) your error is 5ft. • Goal line to Goal line, a football field is 300 feet (known value). If you measure its length and come up with 290ft your error is 10ft. • Even though the first measurement was off by only 5ft, the second measurement which is off by 10ft is much better. • In terms of percentages, the first measurement was off by 50% of the value whereas the second was only off by 3.3%. Error is 5ft out of 10 Error is 10ft but out of 300ft You can have an error of a million miles if you were measuring the distance to the sun but it would only be a 1-2% error because the sun is 93 million miles away! % error = Measured - Accepted • Aluminum has an accepted value of 2.7g/cm3.Suppose you perform an experiment and your results show aluminum as having a density of 2.8g/cm3. What is your percent error? Accepted Get a difference. Compare to Accepted value. Multiply by 100. % error = Measured - Actual A student measured the temperature of boiling water and got an experimental reading of 97.5°C. Calculate the % error. Accepted Get a difference. Compare to Accepted value. Multiply by 100.