2:3 Uncertainty in Measurement

significant figures

All the digits that can be known precisely in a measurement, plus a last estimated digit

Numbers used in unit conversions always have ______ significant digits.

Infinite

2:3 Uncertainty in Measurement

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Precision

a measure of how close a series of measurements are to one another

experimental value

a quantitative value measured during an experiment

When calculating percent error, the denominator in the expression is the--

accepted value

insignificant digits_____

are placeholders for decimals

A basketball player shoots ten free throws and makes every one of them. Her shooting is--

both accurate and precise

Another basketball player shoots ten free throws. Some go off to the left of the basket, some go off to the right, a couple don't reach the basket and three go over the top of the backboard. This player's shooting is--

neither accurate nor precise

The significant figures in a measurement consist of all the certain digits in that measurement plus ___ uncertain or estimated digit.

one

A third basketball player shoots ten free throws. All the shots hit the edge of the backboard on the left side of the basket. This player's shooting is--

precise but not accurate

percent error

the absolute value of the error divided by the accepted value, multiplied by 100%

In rounding numbers in addition and subtraction problems, use _________ in deciding how to round.

the average of significant figures

accepted value

the correct value based on reliable references

The accepted value for the density of aluminum is ______ g/cm3.

2.70

The percent error is ________ if the accepted value and the experimental value are the same.

0%

List the rules for determining significant figures.

1.)Non-zero digits are always significant. 2.)Any zeros between two significant digits are significant. 3.)A final zero or trailing zeros in the decimal portion ONLY are significant

Error

Mistake

How to Distinguish between accuracy and precision in measurements

Precision refers to the closeness of two or more measurements to each other. Using the example above, if you weigh a given substance five times, and get 3.2 kg each time, then your measurement is very precise. Precision is independent of accuracy.

Describe how to calculate the percent error of a measured quantity.

Subtract the accepted value from the experimental value. Take the absolute value of step 1. Divide that answer by the accepted value. Multiply that answer by 100 and add the % symbol to express the answer as a percentage.

Accuracy

The state of being accurate; freedom from mistakes, this exemption arising from carefulness; exactness; nicety; correctness