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Bell-ringer

Bell-ringer.

allene
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Bell-ringer

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  1. Bell-ringer • You are driving in your car down the interstate (70 mph) to Tuscaloosa to watch the University of Alabama crush the Tennessee Volunteers. It appears as though you are going to be late for the kickoff if you don’t speed up. If you are traveling at a speed of 90 km/h, are you breaking the speed limit?

  2. Chapter 2, Section 2:Units of Measurement Coach Kelsoe Chemistry p. 33–42

  3. Units of Measurement • Measurements are quantitative. • We must use units to make any kind of measure. • Imagine getting a treasure map saying, go 5 right, 10 forward, and left 7 to find Captain Jack Sparrow’s treasure. How far would you have to go? • Measurements represent quantities. A quantity is something that has magnitude, size, or amount.

  4. Units of Measurement • Nearly every measurement we make involves a number and a unit. • Many measurements we use have different units, like feet or meters for distance, or gallons or liters for volume.

  5. SI Measurement • Scientists all over the world have agreed on the SI system of measurement. This system was adopted in 1960. • SI stands for Le Système International d’Unités • SI has seven base units, and most other units are derived from these seven. • Some non-SI units are still commonly used. • SI units are defined according to standards of measurement.

  6. SI Base Units • There are 7 base units in the SI system: • Meter (m)- length (l) • Kilogram (kg)- mass (m) • Second (s)- time (t) • Kelvin (K)- temperature (T) • Mole (mol)- amount of substance (n) • Ampere (A)- electric current (I) • Candela (cd)- luminous intensity (Iv)

  7. SI Prefixes • Prefixes can be added to a base unit to represent quantities larger or smaller than the base unit. Some examples of prefixes: Deci- (d) 10-1 Centi- (c) 10-2 Milli- (m) 10-3 Micro- (µ) 10-6 Nano- (n) 10-9 Giga- (G) 109 Mega- (M) 106 Kilo- (k) 103 Hecto- (h) 102 Deka- (da) 101

  8. Bell-ringer • Convert the following quantities: • 525 mL to liters • 7 km to centimeters • 0.003 Gs to seconds • 48 g to micrograms

  9. Mass • The SI unit for mass is the kilogram (kg). • When we measure smaller objects, especially in the lab, we will use grams rather than kilograms. • Mass and weight are different! • Mass is the amount of matter in an object. • Weight is the gravitational pull on matter. • Which measure can change without affecting the substance measured?

  10. Length • The SI unit for length is the meter. • To express longer distances, we use the kilometer. • Most countries use the kilometer when measuring distances, but we use miles. • The centimeter is used for shorter distances.

  11. Derived SI Units • Many SI units are combinations of the standard SI units. • Derived units usually come from multiplying or dividing two standard SI units. • Some combination units are given their own names, like the Pascal. • We can also add prefixes to derived units.

  12. Derived Units

  13. Volume • Volume is the amount of space occupied by an object. It is found by multiplying length x width x height. • The standard unit for volumes of solids is m3. For liquids and gases it is liters (L). • What if we’re comparing volumes of solids to liquids or gases? • One liter (1 L) is equal to 1000 cm3. • One milliliter (1 mL) is equal to 1 cm3. • Also keep in mind that cm3 = cc.

  14. Converting Volumes • If 1 meter is equal to 100 centimeters, then wouldn’t 1 m3 be equal to 100 cm3? • NO!!!!!!!! Here’s why: • 1 meter x 1 meter x 1 meter = 1 m3. • If we measured the same object in cm then: • 100 cm x 100 cm x 100 cm = 1 000 000 cm3 • So we see that 1 m3 does NOT equal 100 cm3! • Remember that mL and cm3 are interchangeable!

  15. Density • Density is the ratio of mass to volume. • Mathematically, we see it like this: • Density = mass/volume or D = m/V • It may be easier to see it like this: m D V

  16. Density • The standard unit for density is kg/m3, but in the lab, this unit is typically way too large. We may use units like g/cm3 or g/L. • Density is a characteristic physical property. It is an intensive property because it doesn’t matter how much we have, the measurement will always be the same. • Different densities is what allows things to float or sink in water. PURE water has a density of 1 g/mL. • If a substance is less dense than water, it floats. • If it is more dense than water, it sinks.

  17. Conversion Factors • A conversion factor is a ratio derived from the equality between two different units that can be used to convert from one unit to the other. • Conversion factors are arranged to cancel out the original unit. • For example, converting 78 feet to yards: • 78 feet x 1 yard = • 26 yards 3 feet

  18. What if… • What if I had chosen the wrong conversion factor? Then… • 78 feet x 3 feet = 234 ft2/yard • Even though 3 feet/1 yard is a correct conversion factor, it does not give us the units we need! 1 yard

  19. Using Multiple Conversion Factors • What if I asked you to convert 110 710 inches to miles? • You would have to do the following: • 110710 inches x 1 foot x 1 mile = 1.75 miles 12 inches 5280 feet It's That Simple!

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