Units of Measurements and Uncertainty:

Objectives:

1.    Identify the metric units of measurement for length, mass, and volume.

2.    List the common metric prefixes and demonstrate how metric prefixes can be used to change units

3.    Explain why measuring always involves estimation.

4.    Describe two causes of uncertainty in measurements.

5.    Explain the difference between accuracy and precision.

Key Terms:

metric system    International System of Units (SI)    base unit    mass    derived unit    volume    metric prefix    precision    accepted value    accuracy

Web Resources:

Notes:

Measurements are required for scientific inquiry.  In order to have meaning a unit must be attached to the measurement.  Throughout the different scientific disciplines you will find the use of the metric system.  Becoming familiar with the standard prefixes will make solving equations and converting units easier.

Uncertainty in measurement:

When making measurements in science it is important to write down all of the digits that a device can give you and, additionally, estimate the next digit.  Remember that measurements are never completely accurate for the following two reasons:

 measuring equipment is never completely free of flaws measurements always involve some degree of estimation

Measuring with a digital display:

Electronic devices take care of estimation for you and record the last digit as the estimated digit.

Estimating with a scale:

Most measuring devices that you will encounter in science classes will use a scale.  Graduated cylinders, spring and triple-beam balances, meter sticks, and clocks are all examples of devices that use scales.  Look at the following 3 examples and estimate the measurements.

What would be the appropriate reading for this graduated cylinder?

What would be the appropriate reading for this graduated cylinder?

What would be the appropriate reading for this graduated cylinder?