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.