1.6 Accuracy and Precision of Measurements

Suppose you go to the store and purchase five 7.5lb bags of potatoes, you decide to test the accuracy of the weight. Bag 1 - 7.2 lbs Bag 2 - 6.9 lbs Bag 3 - 7.6 lbs Bag 4 - 8.1 lbs Bag 5 - 7.9 lbs State the accepted value. State the absolute uncertainty. State the pecentage uncertainty.

Accepted value - 7.5 lbs Absolute uncertainty - 0.6 lbs ( 7.5 - 6.9 or 8.1 - 7.5 ) Percentage uncertainty - 0.6 / 7.5 x 100 = 8% The value can be expressed in the following two ways: Absolute uncertainty = 7.5 +-0.6lbs Percent uncertainty = 7.5 pounds +- 8%

True or False: Measurements must be accurate but not precise.

False: Measurements must be accurate and precise.

How close measurements are to the true value are called _____.

accuracy

How close together the measurments are called _____.

precision

Define accuracy

refers to the closeness of a measurement to the correct value of that measurement.

Define precision

refers to the closeness of measurements to each other

Define percent uncertainty

the absolute uncertainty divided by the accepted values x 100%

State two ways uncertainty can be expressed.

1. absolute uncertainty 2. percent uncertainty

State the factors that contribute to uncertainty in a measurement.

1. limitations of the measuring device 2. the skill of the person taking the measurement 3. irrgularities in object being measured 4. any other factors that affect the outcome.

Define absolute uncertainty

The absolute value of the difference between accepted value and measurement that is furthest away from the accept value.

True or False: Measurements have a numerical value and uncertainty.

True.