Percent Error

• A measure of how inaccurate a measurement is, standardized to how large the measurement is. 

• "Error" in measurement doesn't usually mean "mistake'.  It means the difference between the value found by measurement and the "true value' of the quantity.Ex. an object that has a mass of 120 g may be shown to weigh 130 g by a student.                True weight:           120 g                Measured weight:   130 g                Error:                     +10 g

Why do errors occur?

• Measurement errors arise because of inevitable imperfections in the measuring instrument and limitations of the human eye.

• Errors come in all sizes, and sometimes you need to decide if the error in your measurement is so big that it makes the measurement useless.

Percent Error Formula

Theoretical value = True Value

• Example 1Measuring a LineActual length of line:                     11 cmLength of line when measured:     12 cm

• Error is (Measured Length - Actual Length)Error is (12 cm - 11 cm)  = 1 cm.

Activity

• Find the density of the three given objects

• What do we know about the density of a material?

• How do we find density?

• Mass = balance (g)

• Volume = measurement (cm3) or displacement (ml)

Volume of Regularly Shaped Objects

• Cube or Box = Length X Width X Height

• Cylinder = π X r2 X Height

Find the volume of a cylindrical canister with radius 7 cm and height 12 cm.Solution:

                        

                                               

                                    

Conclusion

• From your data, draw conclusions about the three objects in terms of their densities. What did you learn about them?