Do Now:
Accuracy & Precision
Draw two bullseyes. On one, show three darts
that are accurate. On the other, show three
darts that are precise.
YWBAT
• Explain why metric units are easy to use.
• Identify the temperature units scientists
usually use.
• Calculate the density of a substance.
Measuring Length
• What units can you use to report length?
Measuring Length
• What units can you use to report length?
– Inches
– Feet
– Meters
– Miles
Metric Units
• The standards of measurement used in
science are those of the metric system
• All metric units are based on multiples of 10.
• This makes it easy to convert between units
SI Units
• The metric system was established in France
in 1795
• The International System of Units is a revised
version of the metric system. It is abbreviated
SI after the French name, Le Système
International d’Unités.
• The SI was adopted by international
agreement in 1960.
SI Units
• There are 7 base SI
units
• From these base units,
all other SI units of
measurement can be
derived.
• Derived units are used
for measurements such
as volume, density, and
pressure.
Units of Length
• In SI, the basic unit of length is the meter (m).
• All measurements of length can be expressed
in meters.
• For very large and very small lengths, however
it may be more convenient to use a unit of
length that has a prefix.
Unit Prefixes
Units of Length
• The SI unit for length is a meter (m).
• The prefix milli- means 1/1000
• 1 millimeter = 1/1000 of a meter = 0.001m
• 1 mm = 0.001m
• The prefix kilo means 1000 times larger
• 1 kilometer = 1000 meters
• 1 km = 1000m
Funny Forms
of
1
Units of Volume
• Volume – space occupied by matter
• For a rectangular solid, V = L x W x H
• The SI unit of volume is a cubic meter (m3).
• A more convenient unit of volume for
everyday use is the liter, a non-SI unit.
Units of Volume
• A more convenient unit of volume for
everyday use is the liter. This is a non-SI unit.
• A liter (L) is the volume of a cube
that is 10 centimeters along each
edge.
10cm x 10cm x 10cm = 1000 cm3 = 1L
that
Units of Volume
• A smaller non-SI unit of volume is the
milliliter (mL).
Question?
How many cm3 are equivalent to 1 mL?
Units of Volume
• A smaller non-SI unit of volume is the
milliliter (mL).
Question?
How many cm3 are equivalent to 1 mL?
1 cm3 = 1 mL
The units mL and cm3 are used interchangeably
Measuring Volume
Measuring Volume
Measuring Volume
1. Put on goggles & apron.
2. Get the following equipment for each group.
– 100 mL Graduated cylinder
– 100 mL Beaker
3. Fill beaker with ~ 70 mL water.
4. Pour water into graduated cylinder.
5. Read the volume on the graduated cylinder.
Be sure to:
– get your eye level at the interface.
– read the bottom of the meniscus.
Units of Mass
• Mass – a measure of the quantity of matter.
• The SI unit of mass is the kilogram (kg).
• 1 kg = the mass of 1 L of liquid water at 4°C
• A more convenient unit of volume for
everyday use is the gram (g)
• 1 kg = 1000 grams.
Measuring Mass
Weight
1. Zero your balance
2. Determine the tare weight of your beaker
3. Add ~70mL water to your beaker
4. Weigh the beaker containing the water
5. Calculate the weight of the water.
Weight
• Weight is a force that measures the pull on a
given mass by gravity.
• The weight of an object can change with its
location
Weight
How much would you weigh on the Moon?
Divide your weight on Earth by 6.
Density
• Density is the ratio of the mass of an object to
its volume.
• The relationship between an objects mass and
volume tells you whether it will float or sink.
• Density is an intensive property.
Density
• The SI unit of density is kilograms per cubic
meter (kg/m3).
Increasing density (mass per unit volume)
10 g
19 cm3
10 g
10 cm3
0.53 g/cm3
1.0 g/cm3
10 g
3.7 cm3
10 g
0.88 cm3
2.7 g/cm3
11.4 g/cm3
Density
• Differences in densities cause liquids to
separate into layers.
• As shown below, corn oil floats on top of
water because it is less dense than water.
Corn oil
Water
Corn syrup
Practice
A copper penny has a mass of 3.1g and a volume
of 0.35 cm3. what is the density of copper?
Practice
A copper penny has a mass of 3.1g and a volume
of 0.35 cm3. what is the density of copper?
31 g
3 = 8.9 g/cm3
Density =
=
8.8571
g/cm
0.35 cm3
Density
• The volume of most substances increase as
the temperature increases, while the mass
remains the same.
• The density of a substance generally decrease
as its temperature increases.
• Water is an important exception.
Temperature
Temperature is a measure of how hot or cold an
object is.
• An object’s temperature determines the
direction of heat transfer.
• When two objects at different temperature
are in contact, heat moves from the object at
the higher temperature to the object at the
lower temperature.
Temperature
• The SI unit for temperature is the Kelvin,
named after Lord Kelvin, a Scottish physicist.
• On the Kelvin scale, the freezing point of
water is 273.15 Kelvin (K), and the boiling
point is 373.15 K.
* Note that with the Kelvin scale, the degree sign
is not used.
Temperature
• Another common unit used to measure
temperature is the Celsius scale.
• On the Celsius scale, the freezing point of
water is 0°C, and the boiling point is 100°C.
Comparing the °C and K
Temperature Scales
* Note - The zero point on the Kelvin scale, 0 K, or absolute 0, is
equal to -273.15°C
Comparing the °C and K
Temperature Scales
• One degree on the Celsius scale is equivalent
to one Kelvin on the Kelvin scale.
• To convert between the temperature scales,
Practice
Normal human body temperature is 37°C. What
is this temperature in kelvins?
Practice
Normal human body temperature is 37°C. What
is this temperature in kelvins?
310 K
Practice
A student is performing an experiment and
measures the temperature of water to be
350 K. What is the temperature of the
water in ºC?
Practice
A student is performing an experiment and
measures the temperature of water to be
350 K. What is the temperature of the
water in ºC?
77ºC