Chapter 2: Measurement and Units
 2.1 Space and Time
 2.2 Mass, Matter, and Atoms
 2.3 Experiments and Data
Chapter 2 Objectives

Express lengths in metric and English units.

Convert measurements and calculated quantities between different
units.

Calculate the surface area and volume of simple shapes and solids.

Work with time intervals in hours, minutes, and seconds.

Describe two effects you feel every day that are created by mass.

Describe the mass of objects in grams and kilograms.

Use scientific notation to represent large and small numbers.

Design a controlled experiment.

Create and use a graphical model based on data.
Chapter 2 Vocabulary
 element
 English
system
 graphical
model
 mixture
 speed
 independent
variable
 plasma
 precision
 surface
area
 experimental
variable
 inertia
 exponent
 length
 friction
 liquid
 gas
 mass
 graph
 metric system
 procedure
 time
interval
 scientific
notation
 variable
 SI system
 solid
 volume
 weight
 x-axis
 y-axis
Inv 2.1 Distance and Length
Investigation Key Question:
How do we accurately communicate length and
distance?
2.1 Space and Time
 Space in physics means the three dimensions of
up-down, left-right, and front-back.
 The three dimensions of space are described
with length units, such as meters, inches, and
feet.
 Time provides another dimension for describing
when something occurs.
2.1 Thinking about distance
 Measurement
— is a quantity and a unit
 Distance
— is the amount of space
between two points
— is measured in units of
length
2.1 Two common systems of units
 Science problem solving requires both:
— Metric or S.I. system
— English system
2.1 Two common systems of length
 Almost all fields of science use metric units.
 They make calculations easier because the units
are based on factors of ten.
2.1 Converting from one unit to another
 It is often necessary to take a measurement in
one unit and convert it into a different unit
using conversion factors.
Converting length in yards to
meters
A football field is 100 yards long. What is this
distance expressed in meters?
1.
You are asked for the distance in meters (m).
2.
You are given the distance in yards (yds).
3.
Relationship: 1 yard= 3 feet
4.
100 yds x 3 ft x 0.3048 m = 91.4 m
1 yd
1 ft
2.1 Time
 Two ways to think about time:
— What time is it?
 11:52 a.m. on March 12, 2010
— How much time has passed?
 2 hr: 22 min: 42 sec.
 A quantity of time is often
called a time interval.
2.1 How is time measured?
Converting a mixed time to
seconds
How many seconds are in 1 hour, 26 minutes, and
31.25 seconds?
1.
2.
3.
4.
You are asked for time in seconds.
You are given a time interval in mixed units.
1 hour = 3,600 sec
1 minute = 60 sec
Do the conversion:
1 hour = 3,600 sec
26 minutes = 26 × 60 = 1,560 sec
Add all the seconds:
t = 3,600 + 1,560 + 31.25 = 5,191.25 sec
2.1 Time scales in physics
 Events in the universe happen over a
huge range of time intervals.
 In many experiments, you will be
observing how things change with
time.
Chapter 2: Measurement and Units
 2.1 Space and Time
 2.2 Mass, Matter, and Atoms
 2.3 Experiments and Data
Inv 2.2 Time
Investigation Key Question:
How do we measure and describe time?
2.2 Mass, Matter, and Atoms
 Mass
— is the amount of “stuff” an object contains.
 Two effects mass has on matter:
— Weight
 is the force of the Earth’s gravity pulling down.
 Gravity acts on an object’s mass.
— Inertia
 is the tendency of an object to resist changes in
motion.
 Inertia comes from mass.
2.2 Measuring mass
 Kilogram
— is the mass of 1 liter of
water or 1,000 cubic
centimeters of water.
2.2 Very large and very small numbers
 Because physics covers such a wide range of
values for length, time, and mass you will
need a method of working with large and
small numbers.
 In scientific notation, numbers are written as a
value between 1 and 10, multiplied by a power
of 10 called the exponent.
2.2 Matter and atoms
 A single atom is about
10-10 meters in diameter.
 Aluminum foil is thin but
still more than 200,000
atoms thick.
 Whether matter is a solid,
liquid, or gas depends on
how the atoms are
organized.
2.2 Matter and atoms
 Solids - Atoms in a solid stay together because the energy per
atom is too low to break the bonds between atoms.
 Liquids - Liquids flow because atoms have enough energy to
move around by temporarily breaking and reforming bonds with
neighboring atoms.
 Gases - Gas atoms have enough energy to completely break
bonds with each other.
 Plasma - In plasma, matter becomes ionized as electrons are
broken loose from atoms.
2.2 The diversity of matter
 There is an incredible
diversity of matter around
you.
 This diversity comes from
combining elements into
compounds, then
compounds into mixtures
of compounds.
2.2 The diversity of matter
 Each type of matter is called an element.
 Each element has is own properties, such as
mass and the ability to combine with other
elements.
 There are about 92 different types of atoms in
ordinary matter.
2.2 The diversity of matter
 A compound is a substance that contains two or more
different elements bonded together.
 Water is an example of a compound.
 If you could look at water with a powerful atomic
microscope you would find each particle of water is
made from one oxygen atom and two hydrogen atoms.
2.2 The diversity of matter
 Another compound, glucose, is a sugar in food.
 A single glucose molecule is made of carbon,
oxygen, and hydrogen atoms.
2.2 Matter and atoms
 The matter you normally
experience is made of
mixtures of compounds.
 Wood is a mixture that
contains water and more
than 100 other
compounds.
Chapter 2: Measurement and Units
 2.1 Space and Time
 2.2 Mass, Matter, and Atoms
 2.3 Experiments and Data
Inv 2.3 Matter and Mass
Investigation Key Question:
How is mass described?
2.3 Experiments and Data
 Data are the measurements and calculations
that you make during the experiment.
 Things you measure in experiments are
fundamental quantities.
 Derived quantities can be measured but are
often calculated from things you originally
measured.
2.3 Speed
 Speed
— is a derived quantity calculated from
measurements of distance and time.
 Other derived quantities include
frequency, density, acceleration,
intensity, and energy.
 Each of these units can be broken
down into combinations of the
fundamental units of length, mass, and
time.
Converting a speed from cm/s
to mi/h
 A car on a ramp is measured to go 45 cm in 1.5 s.
What is the speed in miles per hour?
1.
You are asked for speed in mi/h.
2.
You are given speed in cm/s. 4.
3.
Relationships:
— speed = distance ÷ time
— 1 hour = 3,600 s
— 1 mile = 1,609 m
— 1 meter = 100 cm
2.3 Area and volume
 A solid object has
surface area as well as
volume.
 Surface area
— is the measurement of
the extent of an
object’s surface or
area without including
its thickness.
2.3 Area and volume
 Volume
— is a measure of the
space occupied by an
object.
Calculating area and volume
A basketball has a radius of 12.5
cm. Calculate the surface area and
volume of the ball.
1.
You are asked for surface area and volume.
2.
You are given the radius.
3.
Relationships: area: A = 4π r2; volume: V = (4/3)π r3
4.
Solve: Surface area
Volume
A= 4(3.14)(12.5)2 = 1,963 cm2 V= 4 (3.14)(12.5)3 8,181 cm)3
2.3 Density
 Density describes how
much mass is in a given
volume of a material.
 The units of density are
mass divided by volume.
 Identically-sized cubes of
iron, polyethylene, and
glass contain different
amount of mass.
2.3 Density
 Solids range in density from cork, with a density
of 120 kg/m3, to platinum, a precious metal with
a density of 21,500 kg/m3.
2.3 Accuracy and precision
 Accuracy
— is the quality of being exact
and free from error.
— is how close a measurement
is to the true value.
 Precision
— means how small a difference
a measurement can show.
2.3 Variables and relationships
 Factors that affect the results of an experiment are
called variables.
 The science of physics can be thought of as “the search
for the relationships between all the variables that
describe everything.”
 To learn about something specific in nature, scientists
instead select a small set of related variables and define
it as a system.
2.3 Variables for a car on a ramp
2.3 Experimental design
 We do experiments to find out what
happens when we change a variable.
 The variable that is changed is called
the experimental variable.
 The variables that are kept the same
are called the control variables.
 When you change one variable and
control all of the others, we call it a
controlled experiment.
 Controlled experiments are the best
way to get reliable data.
2.3 Experimental design
 The procedure is a
collection of all the
techniques you use to do
an experiment.
 Your experimental
technique is how you
actually do the experiment.
 Each repetition of the
experiment is called a trial.
2.3 Graphical data
 A graph shows how two variables are related.
 By convention, graphs are drawn a certain
way.
 The dependent variable goes on the y-axis
which is vertical.
 The independent variable goes on the
horizontal or x-axis.
2.3 Graphical models
 A graph is a form of a mathematical model
because it shows the connection between two
variables.
 A graphical model uses a graph to make
predictions based on the relationship between
the variables on the x- and y-axes.
2.3 Graphical models
2.3 How to make a graph
1. Decide what to put on the x and y axes.
2. Make a scale by counting boxes to fit your
largest value (multiples of 1, 2, 5 or 10 are
best).
3. Plot your points.
4. Draw a best fit curve.
5. Create a title and label
each axis.
2.3 Recognizing relationships in data
 When there is a relationship between the
variables, a graph shows a clear pattern.
2.3 Recognizing relationships in data
 You can tell how strong the
relationship is from the
pattern.
 If the relationship is weak,
even a big change in one
variable has little effect on
the other.
2.3 Recognizing relationships in data
 When one variable
increases and the other
decreases, it is an inverse
relationship.
 Graphs of inverse
relationships often slope
down to the right.
NANOTECHNOLOGY
 Nanotechnology is the
technology of creating devices
the size of bacteria—or smaller.
 The prefix nano means extremely
small.
 Future applications for
nanotechnology include robots
that can enter your arteries and
clean out blood clots, and
miniature satellites that could
explore the planets.