## Uncertainty in Measurement

### Measurements are made in scientific laboratories, and are commonly used in scientific calculations. To carry out scientific calculations properly it is important to discuss the following concepts;

- Accuracy
- refers to the agreement of a particular value with the true value.

- Precision
- refers to the degree of agreement among several measurements of the same quantity.
- Sample animation differentiating between accuracy and precision.

- Exact numbers
- those numbers that we know exactly. Counting objects is an experiment that can be carried out with complete accuracy.

- Uncertainty
- . numbers that are not known exactly. When we measure lengths (of an object), volumes (of a liquid) or masses (of a solid) the measurements are not exact, they have some degree of uncertainty.

- Sample animation demonstrating uncertainty in measurement.

Significant figures
- A useful method to express the uncertainty in measurement.
- Significant figure rules(see pages 20 and 21 in BLB)
- All nonzero digits are significant
- Zeros between nonzero digits are significant
- Zeros that precede the first nonzero digit are not significant. Reading from left to right begin counting with the first nonzero digit.
- Zeros are significant when they appear; in the middle of a number, at the end of a number that includes a decimal point.
- Zeros at the end of a number without a decimal point are ambiguous. We will assume they are NOT significant.

Practice assigning significant figures.
(Note: The Practicing assigning significant figures is a HyperCard stack. Inorder for this file to run you will have to have HyperCard installed on your computer. If you are on a PC you are OUT OF LUCK. If you are on a Mac there is a chance.)