<p>Essential Concepts: Measurements</p><p>Obj 2.1 Name the metric units of length, mass, time and volume and other common measurements</p><p>Obj 2.2 State the difference between the mass and weight of an object</p><p>1. Weight: Definition: the measure of gravity between two objects (one the objects is usually the Earth). Unit: Newton (N)</p><p>Because the force of gravity between two objects changes with the distance between them, an object's weight varies from place to place (Death Valley vs Mt. Everest); not good for science. </p><p>2. Mass: Definition: a measure of the quantity of matter. Units: the SI unit is the Kilogram (kg), but a gram (g) is often used as standard as well.</p><p>Mass is determined by comparing the mass to a standard using a balance. Mass measurements will be the same anywhere, and are thus useful in science. </p><p>3. Length: Definition: the distance between two points. Unit: the meter (m)</p><p>4. Time: Definition: interval between two occurrences. Unit: the second (s or sec)</p><p>5. Temperature: Definition: the average kinetic energy of the particles in an object. Units: The SI unit is the Kelvin (K) based on "absolute zero," or -273C. Another often used unit is the Celsius degree (C). </p><p>Conversions: K = C + 273. Note there is no degree symbol () with K. </p><p>6. Quantity: Definition: the number of things. Unit: mole (mol): 6.022 x 1023 "things." (Similar idea to a dozen being 12 "things.")</p><p>Other (not SI) metric units often used</p><p>7. Volume: Definition: the space occupied. Unit: liter (L) or milliliter (mL). 1 mL = 1 cm3</p><p>8. Density: Definition: the ration of an objects mass to its volume. Unit: g/cm3 Obj 2.3 Use metric prefixes</p><p>Metric prefixes (memorize those in italics) Prefix Symbol Meaning Example giga- G 1 000 000 000 (109) units 64 gigabyte (GB) hard drive mega- M 1 000 000 (106) units 233 megahertz (MHz) kilo- k 1 000 (103) units 1 kilometer (km) hecto- h 100 (102) units (not much used) deka- dk 10 (101) units (not much used) unit 1 (100) unit 1 meter (1m), 1 gram (1g) deci- d 0.1 (10-1) unit decimeter (dm) centi- c 0.01 (10-2) unit centimeter (cm) milli- m 0.001 (10-3) unit millimeter (mm) micro-  ("mew") 0.000 001 (10-6) unit micrometer (mm) nano- n 0.000 000 001 (10-9) unit nanosecond (ns) pico- p 0.000 000 000 001 (10-12) un picometer (pm) </p><p>Obj 2.4 Distinguish between the accuracy and precision of a measurement</p><p>Accuracy: how close a measurement it to the true value.</p><p>Precision: how close measurements are to one another. Note: precise measurements are not always accurate and vice versa.</p><p>If the true value is 23 mm, the measurements 21 mm, 24 mm, 20 mm, 25 mm are accurate but not very precise; while the measurements 18 mm, 19 mm, 17 mm, 18 mm are precise but not accurate. The measurements 22mm, 24 mm, 23 mm are both accurate and precise. </p>