Chapter 1 The Nature of Science 1.2 Standards of Measurement PHYSICAL SCIENCE Chapter 1 The Nature of Science 1.2 Standards of Measurement

1.2 Standards of Measurement Objectives Name the prefixes used in SI and indicate what multiple of ten each one represents. Identify SI units and symbols for length, volume, mass, density, time, and temperature. Convert related SI units.

Units and Standards A standard is an exact quantity that people agree to use to compare measurements. Cubits (forearm tip from tip of middle finger to bottom of elbow) and spans (distance from end of little finger to end of thumb of a spread hand) were used in ancient times as units of measurement. What problems do you expect with these units?

Measurement Systems Both a number and a unit must be used for a measurement to make sense. English system of measurement commonly used in US. Most countries use the metric system. In 1960, an improved metric system was developed – SI (International System of Units – Le Systeme Internationale d’Unites) SI standards are universally understood and accepted by scientists globally.

Measurement Systems Every type of SI measurement has a base unit. SI is based on multiples of ten. Prefixes are used with the base unit name to indicate the multiple of ten to be used.

Measurement Systems Quantity Measured Unit Symbol Prefix Symbol Length meter m Mass kilogram kg Time second s Electric Current ampere A Temperature kelvin K Amount of Substance mole mol Intensity of Light candela cd Prefix Symbol Multiplying Factor Kilo- k 1,000 Deci- d 0.1 Centi- c 0.01 Milli- m 0.001 Micro- μ 0.000001 Nano- n 0.000000001

Measurement Systems A conversion factor is a ratio that is equal to one, and is used to change one unit to another unit. See “Applying Math” pg. 16. http://www.wonderwhizkids.com/conceptmaps/conversion_factor_units.html

Measuring Distance Length is the distance between two points. SI basic unit of length is the meter. Rulers and metersticks are used to measure distances. Choose appropriate unit of length to avoid multiple zeros.

Measuring Volume The amount of space occupied by an object is its volume. The formula for a block is length x width x height. The most common units for liquid volume are liters and milliliters. One milliliter is equivalent to one cubic centimeter.

Measuring Matter Mass is the measurement of a quantity of matter in an object. Density is the mass per unit volume of a material. Density may be found by dividing an objects mass by its volume. A unit of measurement that can only be found by combining other units is called a derived unit.

Measuring Time and Temperature SI unit for time is the second. In science, temperature is often measured on the Celsius scale. On Celsius scale, water freezes at 0°C and boils at 100°C. Average human body temperature is 37°C Typical room temperature is between 21 - 24°C. Kelvin is SI unit of temperature. On Kelvin scale, water freezes at 273 K, and boils at 373 K.