Standards of Measurement

Physical Science

Mr. Bostrom

Units and Standards

1. Standards – exact quantity that people agree to use for comparison

2. SI – standard system of measurement 1. All scientists use this system2. Metric vs English System

1. Americans use the English System1. Example: Feet and Inches

2. 1970’s we tried to convert to the metric system1. We failed miserably

Common SI Prefixes Prefix Meaning• Mega (M) 1000000 • Kilo (k) 1000• Hecto (h) 100• Deka or Deca (da) 10 • Base Unit 1• Deci (d) 0.1• Centi (c) 0.01• Milli (m) 0.001• Micro (µ) 0.000001• Nano (n) 0.000000001• Pico (p) 0.000000000001

SI Base Units

• Length – Meter (m)

• Liter – Volume (L)

• Mass – Gram (g)

• Time – second (s)

• Electric Current – Ampere (A)

• Temperature – Kelvin (K)

How do prefixes and base units work together

• Example: Kilogram or kg– Kilo = 1000– Gram is the base unit of mass– 1 Kilogram = 1000 g

Converting within the Metric System

• Rule #1: Always remember that your base unit is 1

• Rule #2: If you add a prefix onto the base unit you multiply by what the

prefix represents

– Example: 1 kg = 1000 g or (1000 x 1)

2 kg = 2000 g or (1000 x 2)

What do you do when you are not starting from or converting to your

base unit?• Example: 100mm = ?km (This is where it

can get tricky)• The rule of thumb is:

– If you are increasing in size you move the decimal point to the left

– If you are decreasing in size you move the decimal point to the right

• km are bigger than mm so you move the decimal to the left

Sounds simple but how many decimal places do you move?

• In this case 6– How did I know that– There are 4 ways to do this:

• First way: divide the prefix value of the measurement you are starting with by the prefix value you want to convert to and then multiply the answer by the coefficient

» Milli = .001, Kilo = 1000 ( .001/1000) x 100 = 0.0001 (This is the final answer) You know it was six places because you started with

100.0 and to get 0.0001 you need to move the decimal 6 places to the left

Converting Contineud

Second Way:

Kilo Hecto Deca Meter Deci Centi Milli

a. Find the prefix you are starting withb. Then find the prefix you are converting to

c. Count how many prefixes you must pass to get to the

final prefix- Always remember: 1. if you are getting larger the decimal goes to the left 2. If you are getting smaller the decimal goes to

the right

3rd Way • To convert from larger to smaller units,

multiply the coefficient by the difference between units

• To convert from smaller to larger units, divide the coefficient by the difference between units

Example: 1 million mm in a km, so divide 100 by 1000000

4th Way Factor-Label Method

• Multiply your coefficient by conversion factor that equals one:– Trying to convert mm to km

• 1 km = 1000000mm – The conversion factor is (1 km/1000000 mm) = 1

– Example: 100 mm x (1km/1000000mm)• 1 km/1000000mm = 1

Volume

• Defined as the amount of space occupied by an object

• It does not just measure liquid

How do you calculate volume• Liquid – with a graduated cylinder• Solid (2 possible ways)

1. Measure the height, length, and width and then multiply the three.

• Length x Width x Height

2. For a solid in which you can’t measure the length, width, and height you need to use a measuring cup or graduated cylinder

- Using a graduated cylinder record a known volume of water and then drop the object into the water

- Record the new volume- Take the difference between the two volumes and that is

the volume of the object

What unit is volume recorded in?

• Because you are measuring height, width, and length the unit is cm3

• Volume of a liquid would be in liters– 1 cm3 = 1 ml

• When you combine SI units the outcome is known as a derived unit.– Examples: meters/second grams/ml

Density• Mass per unit volume of a material

• Units for density are generally g/cm3

• To determine an objects density you need to divide the object’s mass by it’s volume

– Example: If an object weighs 5 g and has a volume of 10 cm3 what is the object’s density

• 5 g / 10 cm3 = .5 g/ cm3

• The density of water is 1 g/ml

Temperature

• Generally measured in Celsius (°C) for most scientific work, however the SI unit for temperature is Kelvin (K)

– How do you convert K to °C or °C to K?

• To convert °C to K you need to add 273 K = °C + 273

• To convert K to °C you need to subtract 273 °C = K - 273