Quantities and Units

Metric System
a system of measurement based on the powers of ten

SI – International System
a uniform modification of the metric system used by scientists

Length
the distance between two points
 

Units for Length	SI	US
	meter m	inch in . foot ft . mile mi

Example:
A 1973 Mustang Grande is 4.923 m in length.

Volume
the amount of space a substance occupies

volume = length x width x height  (3 dimensions)
 
 

Units for Volume	SI	US
	cubic meter m3 . metric:  liter L	fluid ounce fl oz . quart qt . gallon gal

One cubic meter is defined as 1,000 liters.

1 m³ = 1,000 L

Example:
In Europe, rather than being sold by the gallon, gasoline is sold by the liter.

One gallon is just a little more than 4 liters— that is, a liter is just a little less than a quart.

Mass
the quantity of material an object contains

(not to be confused with volume, which is how much space that material takes up, or occupies)
 

Units for Mass	SI
	kilograms kg .        metric: grams g 1 kg = 1,000 g	.

• Mass is NOT the same as weight (except in Earth’s gravity).
• Mass is NOT affected by gravity.

Weight
the measurement of the gravitational pull on the mass of an object
 

Units for Weight	.	US
	.	ounce oz . pound lb

Example:  The Difference Between Mass & Weight

Astronaut with mass of 75.0 kg
weighs 165 lbs on Earth

165 lbs	= 2.20	pounds
75.0 kg		kilogram

.
• Only under Earth’s gravity can we say that 1 kg = 2.20 lbs

 
• The moon has 1/6 the gravitational pull of the Earth.

Astronaut weighs 27.5 lbs on the moon
but still has mass of 75.0 kg

Density
the relationship between the mass of an object and its volume
 

Determining the Density of Solids
When a solid is completely submerged, it displaces a volume of water that is equal to its own volume.
By dividing the mass of the solid by its measured volume, the density of the solid can be calculated.

Example:
A zinc sample has a mass of 68.60 g and when placed in a graduated cylinder of water, the level rises from 35.5 mL to 45.0 mL.  What is the density of zinc?

The volume of the sample is 45.0 mL – 35.5 mL = 9.5 mL.
 

Specific Gravity (sp gr)
a ratio between the density of a substance and the density of water
(1.00 g/mL @ 4 °C)
 

In the calculations for specific gravity, the units must match.
Then all units cancel, leaving only a number.

• Specific Gravity has no units!

Example:
By the definition of specific gravity, will a cork from a bottle float?

density of cork = 0.26 g/mL
 

• If the specific gravity of a substance is less than one, it floats!

Temperature
a measure of the average energy of particles in matter;
temperature determines the direction of heat transfer—from hot to cold
 

Units for Temperature	SI	US
	Kelvin K . (no ° symbol) .         metric: Celsius °C	Fahrenheit °F

0° C = 273 K  = temperature at which water freezes (32 °F)
100° C = 373 K = temperature at which water boils (212 °F)

In the Kelvin Temperature Scale,
0 K is lowest possible temperature—
the temperature at which all motion stops.

Example:
The hottest temperature ever recorded on Earth was 56.7 °C (134.1 °F) on July 10, 1913 in Furnace Creek (Greenland Ranch), Death Valley, California.

Energy
the ability to do work or to heat
 

Units for Energy	SI	US
	Joule J metric calorie cal

1 calorie is the quantity of heat that raises 1 gram of H₂O by 1 °C

1 cal = 4.184 J and 1 J = 0.2390 cal

Time
a period or interval used to measure the sequence or duration of events
 

Units for Time	SI	US
	second s	second sec minute min hour hr

Example:
To heat one liter of water using a regular stove, it will take about 10-15 minutes (600 to 900 s) for water to reach the boiling point, depending upon elevation above sea level.

Intensive Properties
A physical property that depends on the type of material chosen,  not on the amount of it.

Examples:  Melting point & density are intensive properties.
                  Every element has a unique melting point and density.

                  Copper has a different melting point and a different density than lead.

Extensive Properties
A physical property that depends on the amount of material chosen, no matter the type of material.

Examples:  Volume & Mass are extensive properties.
                  The volume and mass of any element depends on the amount of
                   the element in the sample, no matter what element it is.

When are units of measurement used?
What system of measurement do scientists use?
 

Practice Problems Answer the following questions:

1. State the quantity being measured (length, mass, volume, temperature, or time) being measured indicated by the abbreviation of the unit in each of the following: . a) 4.6 g b) 1.8 m3 c) 14 s d) 7.2 kg/m3 e) 45 m f) 315 K

2. State the name of the metric unit AND abbreviation  you would use to express the quantity in each of the following: . a) length of a football field c) mass of salt in a shaker . b) daytime temperature d) volume of soda in a bottle

3. When a lead weight with a mass of 226 g is sumberged in 200.0 mL of water, the level rises to 220.0 mL. Use this information to calculate the density of lead.

4. A sample of copper has a mass of 44.65 g and a volume of 5.0 mL. What is the density of copper?

5. When a sample of black ironwood, a tree grown in southern Florida, with a mass 9.485 g is placed in a graduated cylinder containing 51 mL of water, the level rises to 58 mL. Will the sample of ironwood float?

6. Determine whether the following are intensive or extensive properties: . a) length d) density . b) specific gravity e) freezing point . c) mass f) volume