Why do we need a measurement system? When experiments are performed there are almost always some observations where questions like "how fast", "how far", or "how much" must be answered. The only way to answer these questions is through measuring. Because of this, numbers in science will always have "units". These units are just as important as the numbers when communicating observations. Never write a number without its units.

A "standard" is something that is used as a comparison for measuring. Two things are important for any standard:

• The standard must be available for everyone to use when checking measurements. This means a standard should be something in nature that is the same all over the earth.
• The standard must never vary.

Know these SI units:

• Meter - unit of length
• Kilogram - unit of mass
• Liter - unit of volume
• Celsius degrees - unit of temperature
  • 2 of the 3 temperature scales are used in science.
• Second - unit of time

Know these SI prefixes:

• Mega - 1 000 000
• Kilo - 1 000
• Centi - 0.01
• Milli - 0.001

Some of the common SI unit relationships used in science classes:

• 1 liter = 1 cubic decimeter (dm³)
• 1 cubic centimeter (cm³) = 1 milliliter (ml)

Using the Metric System is difficult only because:

• You have grown up using the English System.
• When you use the Metric System, your mind is comparing it to the English System.

Unit Conversions:

Having to convert one type of unit to another is a common problem in science. There are exact conversion factors that can be used to change units in one system to units in the other. Here is a page of useful conversion factors. We will not stress conversion between the systems in this class. All our measurements will be done using SI units. The table below might help you begin to visualize the size of the units of the metric system.

Research Links:

• A Question of Scale - A study on the effect of adding another zero
• More Information - Frontier High School Chemistry Class
• Unit Converters - Judi Wolinsky