Section 2 Units of Measurement Chapter 2 Objectives- after viewing this lesson you should be able to do the following: Distinguish between a quantity, a unit, and a measurement standard. Name and use SI base units. Name and use SI derived units. Name and use metric prefixes. Perform metric conversions.

Objectives Distinguish between mass and weight. Perform density calculations. Transform a statement of equality into a conversion factor. Use factor-label method, aka dimensional analysis, to solve problems.

Chapter 2 Units of Measurement Measurements represent quantities. Section 2 Units of Measurement Chapter 2 Units of Measurement Measurements represent quantities. A quantity is something that has magnitude, size, or amount. the liter is a unit of measurement used to represent volume volume is a quantity The choice of unit depends on the quantity being measured.

Chapter 2 SI Measurement Section 2 Units of Measurement Chapter 2 SI Measurement Scientists all over the world have agreed on a single measurement system called Le Système International d’Unités, abbreviated SI. SI has seven base units most other units are derived from these seven A base unit is independent of other units A base unit is a defined unit in a system of measurement that is based on an object or event in the physical world.

SI (Le Systéme International d´Unités) Visual Concepts Chapter 2 SI (Le Systéme International d´Unités)

Section 2 Units of Measurement Chapter 2 SI Base Units

Chapter 2 SI Base Units Mass Section 2 Units of Measurement Chapter 2 SI Base Units Mass Mass is a measure of the quantity or amount of matter contained in an object. Weight is a measure of the gravitational pull on a mass. Weight does not equal mass.

Chapter 2 SI Base Units Length, Temperature, Amt. of Substance Section 2 Units of Measurement Chapter 2 SI Base Units Length, Temperature, Amt. of Substance Length is a measure of distance. Temperature is a measure of the average kinetic energy in a sample of matter. ( KE=1/2m . V2 ) The Amount of Substance measures the total number of individual particles of matter contained in a sample of matter. ( Avagadro’s # = 1 mole= 6.02 x 1023 )

Chapter 2 Derived SI Units Section 2 Units of Measurement Chapter 2 Derived SI Units Combinations of SI base units form derived units. pressure is measured in kg/m•s2, or pascals pressure is force per unit area

Derived SI Units, continued Section 2 Units of Measurement Chapter 2 Derived SI Units, continued Volume Volume is the amount of space occupied by an object. The derived SI unit is cubic meters, m3 The cubic centimeter, cm3, is often used The liter, L, is a non-SI unit 1 L = 1000 cm3 1 mL = 1 cm3

Visual Concepts Chapter 2 Volume

Measuring the Volume of Liquids Visual Concepts Chapter 2 Measuring the Volume of Liquids

Derived SI Units, continued Section 2 Units of Measurement Chapter 2 Derived SI Units, continued Force is a mass accelerating . The derived SI unit is the Newton , N,, kgm/s2 Velocity is distance covered per unit time, m/s Acceleration is a change in velocity over time, m/s2

Derived SI Units, continued Section 2 Units of Measurement Chapter 2 Derived SI Units, continued Energy is applied force through a distance. The derived SI unit is the Joule , J, kgm2/s2 Concentration is amount of substance per unit volume, mol/m3

Derived SI Units, continued Section 2 Units of Measurement Chapter 2 Derived SI Units, continued Density Density is the ratio of mass to volume, or mass divided by volume. The derived SI unit is kilograms per cubic meter, kg/m3 g/cm3 or g/mL are also used Density is a characteristic physical property of a substance.

Derived SI Units, continued Section 2 Units of Measurement Chapter 2 Derived SI Units, continued Density Density can be used as one property to help identify a substance

Visual Concepts Chapter 2 Equation for Density

Derived SI Units, continued Section 2 Units of Measurement Chapter 2 Derived SI Units, continued Sample Problem A A sample of aluminum metal has a mass of 8.4 g. The volume of the sample is 3.1 cm3. Calculate the density of aluminum.

Derived SI Units, continued Section 2 Units of Measurement Chapter 2 Derived SI Units, continued Sample Problem A Solution Given: mass (m) = 8.4 g volume (V) = 3.1 cm3 Unknown: density (D) Solution:

Chapter 2 Conversion Factors Section 2 Units of Measurement Chapter 2 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. example: How quarters and dollars are related

Visual Concepts Chapter 2 Conversion Factor

Conversion Factors, continued Section 2 Units of Measurement Chapter 2 Conversion Factors, continued Dimensional analysis is a mathematical technique that allows you to use units to solve problems involving measurements. quantity sought = quantity given × conversion factor example: the number of quarters in 12 dollars number of quarters = 12 dollars × conversion factor

Using Conversion Factors Section 2 Units of Measurement Chapter 2 Using Conversion Factors

Conversion Factors, continued Section 2 Units of Measurement Chapter 2 Conversion Factors, continued Deriving Conversion Factors You can derive conversion factors if you know the relationship between the unit you have and the unit you want. example: conversion factors for meters and decimeters

Chapter 2 Base units can be too large or too small for some measurements, so the base units may be modified by attaching prefixes.

Conversion Factors, continued Section 2 Units of Measurement Chapter 2 Conversion Factors, continued Sample Problem B Express a mass of 5.712 grams in milligrams and in kilograms. Keep in mind that all “base” units such as the gram in this example are what the metric prefixes are affixed to in order to change the value on the unit. For conversion purposes all of these “base “ units are assigned a value of 100 (100=1)

Conversion Factors, continued Section 2 Units of Measurement Chapter 2 Conversion Factors, continued Sample Problem B Solution Express a mass of 5.712 grams in milligrams and in kilograms. Given: 5.712 g Unknown: mass in mg and kg Solution: mg 1 g = 1000 mg Possible conversion factors:

Conversion Factors, continued Section 2 Units of Measurement Chapter 2 Conversion Factors, continued Sample Problem B Solution, continued Express a mass of 5.712 grams in milligrams and in kilograms. Given: 5.712 g Unknown: mass in mg and kg Solution: kg 1 000 g = 1 kg Possible conversion factors:

Chapter 2 Multiple Choice Standardized Test Preparation Chapter 2 Multiple Choice 8. A measurement of 23 465 mg converted to grams equals A. 2.3465 g. B. 23.465 g. C. 234.65 g. D. 0.23465 g.

Chapter 2 Multiple Choice Standardized Test Preparation Chapter 2 Multiple Choice 8. A measurement of 23 465 mg converted to grams equals A. 2.3465 g. B. 23.465 g. C. 234.65 g. D. 0.23465 g.