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Measurements and Solving Problems

Measurements and Solving Problems. 2.1 Units of Measurements The SI Measurement System 1. unit of measurement: physical quantity of a defined size 2. standard of measurement: objects or natural phenomena of constant value,

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Measurements and Solving Problems

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  1. Measurements and Solving Problems

  2. 2.1 Units of Measurements The SI Measurement System 1. unit of measurement: physical quantity of a defined size 2. standard of measurement: objects or natural phenomena of constant value, easy to preserve and reproduce

  3. Seven Fundamental SI Units 1. Length standard unit is the meter  meter: the distance light travels in a vacuum during a time interval 2. Mass  standard unit is the kilogram

  4. 3. Time  standard unit for time is the second 4. Temperature  based on Kelvin 5. Amount of substance : mole 6. Electric current: ampere 7. Luminous intensity: candela

  5. Prefix Symbol Exponential factor Giga G 109 Mega M 106 Kilo k 103 Hectoh 102 Decada 101 Decid 10-1 Centic 10-2 Millim 10-3 Micro υ 10-6 Nanon 10-9

  6. Units of measurement in calculations • Factor-label method  A problem solving method based on using units as algebraic factors. • Unit conversion  A ratio derived from the equality between two different units and can be used to convert from one unit to the other.

  7. Examples: a. Convert 75 dollars to quarters 75 dollars x4 quarters = 1 dollar b. Convert 92 mg to g 92 mg x1 g = 1000 mg

  8. c. Convert 25 cm to m. d. Convert 72.0 g to micrograms

  9. Derived SI Units • A unit that can be obtained from combinations of fundamental units. • Volume  The amount of space occupied by an object  length x width x height cm x cm x cm = cm3 **** 1 L = 1000 mL = 1000 cm3

  10. 3. Density  Relates the mass of substance to its volume, or its mass per unit volume  density = mass volume or d = m v

  11.  units for density: gases: kg m3 solid: g cm3 liquid: g mL

  12. Example: 1. Find the density of a piece of aluminum with a volume of 4.0 cm3 and a mass of 10.8 g. Is aluminum more dense or less dense than lead? (Dlead = 11.35 g/cm3)

  13. 2.2 Heat and Temperature 1. Temperature: is the measure of the average kinetic energy of the particles in a sample of matter 2. Heat (heat energy): the sum total of the kinetic energies of the particles in a sample of matter

  14. 3. Units of temperature  degree Celsius water freezes at 0 °C water boils at 100 °C  degree Fahrenheit water freezes at 32 °F water boils at 212 °F Kelvin K = 273 + °C

  15.  Temperature conversions: °C = 5/9 x ( °F -32) °F = 9/5(°C) + 32 4. Units of heat a. joule (J): SI unit of heat b. calorie: the quantity of heat required to raise the temperature of 1 g of water 1 °C

  16. **** 1 cal = 4.184 J c. Ex. Convert 275 cal to joules and kilojoules. 1. 2.

  17. 5. Heat capacity and specific heat  three things determine heat change 1. the nature of the matter changing temperature 2. the mass 3. the size of the temperature change

  18.  heat capacity: amount of heat energy needed to raise the temperature of a given sample of matter by one Celsius degree specific heat: the amount of heat energy required to raise the temperature of 1 g of a substance by one Celsius degree

  19. Common specific heats

  20.  equation: q = mCΔT where q = heat (absorbed or released) m = mass C = specific heat ΔT = final temp – initial temp

  21.  Example: A 4.0 g sample of glass was heated from 1 °C to 41 °C, and was found to have a specific heat of 0.20 J/g°C. How much heat was gained?

  22. 2.3 Using Scientific measurements Accuracy and precision Accuracy: refers to the closeness of a measurement to the true or accepted value of the quantity measured Precision: refers to the agreement among the numerical values of a set of measurements of the same quantity made in the same way

  23. percent error: % error = accepted value – experimental value x 100 accepted value Significant figures: See handout Reading scales: 1. 2. 3.

  24. Quantitative Problems 1. How many cm are in 35 inches? 2. How many gallons are in 50 liters? 3. How many km/min is 32 mi/hr?

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