Chapter 2

Measuring and Equations

Today’s Objectives

• Understand the difference between qualitative and quantitative observations, and that measurements are quantitative

• Know the SI base unit used to measure each of the following quantities: length, mass, temperature, and amount of substance.

• For the metric prefixes know the meaning of the prefix and be able to convert between them.

• Know the two derived units: volume and density

Uncertainty in Measurement

• Your measurements are only as good as your instrument

• In measurement, always estimate the last digit.

Reliability in Measurements

• Precise measurements will give the same results again and again

• Accuracy is how close you are to the accepted value

Qualitative and Quantitative• Qualitative – Deals with descriptions. • Data can be observed but not measured. • Colors, textures, smells, tastes, appearance, beauty, etc. • Qualitative → Quality

• Quantitative-Deals with numbers. • Data which can be measured. • Length, height, area, volume, weight, speed, time,

temperature, humidity, sound levels, cost, members, ages, etc.

• Quantitative → Quantity 

SI units

• SI units a revised from of the metric system

• SI base units are fundamental physical units

• Si derived units are combinations of SI base units

What are the SI Units For

• Mass• Length• Volume• Temperature• Time

Do you know the abbreviation and value for..

• Kilo• Hetco• Deka• Deci• Centi• Milli

Converting Metric Units

• SI units based upon 10s makes converting metric units simple

• Begin with the prefix given and move the decimal the same number and direction to the desired prefix

• Remember when above kilo and below milli- to move the decimal three spaces

Converting

Practice

• A soda can holds 355 mL convert to L

• Convert 76 km to meters• Convert 18 mm to cm• A Thumb drive holds 512 Megabytes

convert to Kilobytes

Densitydensity = mass / volume

Volume Measuredby

1. Graduated Cylinder2. l x w x h3. Water Displacement

SOLVING

• PLUG IN ALL GIVENS• M=• V=• D= WHAT ARE YOU SOLVING FOR?

A metal block has a mass of .075 kg and a volume of 22 cubic centimeters. Calculate

the density.

An aquarium has dimensions of 25.0 cm by 68.5 cm by 34.0 cm.

If the mass of the aquarium if 2.3 kg, calculate the density.

SOLVING FOR MASS

• M=V X D• IRON HAS A KNOWN DENSITY OF 7.87

g/cm3 What would be the mass of a 2.5 cm3 piece of iron?

M=V=D=Plug and solve!

Solving for Volume

• V = m/d • Mercury has a density of 13.5 g/cm3

How much space would 50.0 g of mercury occupy?

• D=• M=• V=• Plug and solve!

Pyramid

Density

• A student finds a rock on the way to school. In laboratory he determines that the volume of the rock is 22.7 cm3, and the mass in 39.943g. What is the density of the rock?

• 1.76 g/cm3

Density

• How many grams of tin wood occupy 5.5 L, if it has a density of 7.265g/cm3

• 4 x 104 g

• The density of lead is 11.342 g/cm3. what would be the volume of a 200.0 g sample of this metal?

• 17.63 cm3

Water & DensityWater has a density of 1.0

g/ml at 4o C

Any object with a density greater will sink

less will float

1cm3 = 1cc = 1ml

Other

% = part/whole x 100%

Calculate the percentage of people in this class wearing

glasses

% Error = (measured value – accepted

value)/ accepted value

When measuring the density of gold you find a value of 20.9

g/cm3 . The accepted value is 19.3 g/cm3

Today’s objectives

• For two different units of measurement, be able to determine the appropriate conversion factor

• Be able to use the appropriate conversion factor to convert from one unit of measurement to another in both one-step and multi-step problems.

Dimensional Analysis

• Technique of converting between units.

• A unit quantity shows how units are related (1 mile = 5280 feet)

• Units can be multiplied and divided (g/ml)

Dimensional Analysis

• Determine the units that you are trying to get to.

• Write down the appropriate conversion factor.

• Set up the problem so the units when multiplied or divided give the desired units

• Solve the problem

How many gallons are in 455 liters? (1 gal = 3.785 L)

Dimensional Analysis

• Combine the steps into one longer conversion.

How many seconds are in 5.5 hours?

How many centimeters are in 1.3 miles? (1 mi = 5280 ft)

How many cubic centimeters are in 5.00 quarts of milk? (1 gal =

3.785 Liters)