Motion
Unit 1: Motion
Chapter 1: Describing the Physical
Universe
 1.1
The Science of Physics
 1.2
Distance, Time, and Measurement
 1.3
Speed
1.1 Investigation: Measuring Time
Key Question:
How do we measure and
describe time?
Objectives:

Use electronic timing equipment and photogates.

Use units of time in calculations and conversions.

Correctly apply the terms accuracy, precision, and
resolution to scientific instruments and measurements.
The Science of Physics
 Physics
is a type of
science that studies
matter and energy.
 Everything
in the
universe is believed to
be either matter or
energy.
The Science of Physics
—
Matter is anything that has mass and takes up
space.
— Energy is a measure of a system’s ability to
change or create change in other systems.
The Science of Physics
 A natural
law is a rule that describes an action or set
of actions in the universe.
 Sometimes
a natural law, like Newton’s second law
of motion, can be expressed by a mathematical
equation.
 We
do not know all of the natural laws, so there is a
lot left for students like you to discover!
Systems and variables
 A variable
is a factor that affects the behavior of the
system.
 When
you are trying to find out how a system works,
you look for relationships between the important
variables of the system.
The scientific method

Learning by chance is one way to learn.

The scientific method is a much more
dependable way to learn and gather information.

Key parts include:
1. the hypothesis, a tentative, testable statement
that tries to explain a set of scientific
observations.
2. the experiment, a situation specifically set up to
test or investigate a hypothesis.
The scientific method

1. Scientists observe nature, then develop or revise
hypotheses about how things work.

2. The hypotheses are tested against evidence collected from
observations and experiments.

3. Any hypothesis that correctly accounts for all evidence from
the observations and experiments is a potentially-correct
theory.

4. A theory is continually tested by collecting new and different
evidence. Even one single piece of evidence that does not
agree with a theory will force scientists to return to the first
step.
Scientific theories
 In
science, the word theory is used differently than in
everyday use.
 A scientific
theory is a comprehensive, well-tested
description of how and why a process in nature
works the way it does.
Scientific theories
 The
purpose of scientific research is to do
experiments which show that existing theories do not
give the right prediction.
 A theory
that correctly explains 1,000 experiments
but fails to explain the 1,001st cannot be wholly
complete.
Scientific theories
 It
is important to be able to distinguish between
pseudoscience and science.
 “The
word pseudo means fake,” says professor
Coker, of the Physics Department at the University of
Texas.
 Beware
 Some
of “science” you find on the Internet.
of it is correct, but much of it is not.
Investigation systems

Experiments on systems
usually have a question
associated with them.
 An
example would be
“How does the steepness
of a ramp affect the speed
of a ball?”
Investigation systems

The variable causing the
change in the system is
called the independent
variable.
 The
angle of the ramp is
the independent variable
in this example.
Investigation systems

The variable that may
show the effect of those
changes is called the
dependent variable.
 The
speed of the ball is
the dependent variable.
Investigation systems

In an ideal experiment,
you change only one
variable at a time.
 You
keep all of the other
variables the same.
 A variable
that is kept the
same is called a control
variable.
What variables should be
controlled in this system?
Scientific evidence

There are exacting rules defining
what counts as scientific evidence.

Scientific evidence can include
numbers, tables, graphs, words,
pictures, sound recordings, or
other information.

Scientific evidence must also be
objective and repeatable.
Models
 In
physics, a model links the variables in a system
through cause-and-effect relationships.
 Our
car-and-track system links height and speed to
the idea of energy.
 This
conceptual model is known as the law of
conservation of energy, a natural law of physics.
Unit 1: Motion
Chapter 1: Describing the Physical
Universe
 1.1
The Science of Physics
 1.2
Distance, Time, and Measurement
 1.3
Speed
1.2 Investigation: Speed
Key Question:
Can you predict the speed of
the car as it moves down
the track?
Objectives:
Predict what happens to a car’s speed as it travels down a
track.
 Create and interpret a speed vs. position graph.
 Use a graph to make a prediction that can be quantitatively
tested.
 Calculate the percent error between a measurement and a
prediction.

Measurement
 A measurement
is a
precise value that tells how
much.
 A measurement
communicates a quantity,
and a unit.
 For
example, 2 meters is a
measurement.
Distance
 Distance
is the amount
of separation between
two unique points.
 Distance
is measured in
units of length.
 Commonly
—
used units of length include:
inches,
— miles,
— centimeters,
— meters, and
— kilometers.
Two systems of measurement
 The
English System is used for everyday
measurements in the United States.
 During
the 1800s, a new system of measurement—
the Metric System—was developed in France and
was quickly adopted.
 In
1960, the Metric System was revised and
simplified, and a new name was adopted—the
International System of Units, or SI.
Two systems of measurement
 Almost
all fields of science worldwide use SI units
because they are so much easier to work with.
 In
SI, factors of 10 are easier to calculate
mathematically.
SI prefixes
 Today,
the United States
is the only industrialized
nation that has not
switched completely to
SI.
Measuring time
 A quantity
of time is called a
time interval.
 Most
problems in physics
measure time in seconds,
so you may need to convert
from hours or minutes.
Time scales in physics
 The
second (s) is the basic unit of time in both the SI
and English systems.
 In
many experiments, you will observe how things
change with time.
Accuracy, precision, and resolution
 The
words accuracy and
precision also have different
meanings in science than every
day use.
— Accuracy is how close a
measurement is to its accepted
or “true” value.
— Precision describes how close
together several repeated
measurements or events are to
one another.
Accuracy, precision, and resolution
 Resolution
is another important term to understand
when you are working with measured quantities.
 Resolution
is a reference to the smallest interval that
can be measured.
Working with measurements
 All
measurements involve a degree of uncertainty.
 It
is impossible to make a measurement of the exact
true value of anything, except when counting.
 Significant
digits are the meaningful digits in a
measured quantity.

Mathematic answers involving measured quantities
should have no more significant digits than the
starting measurement with the least number of
significant digits.
Unit 1: Motion
Chapter 1: Describing the Physical
Universe
 1.1
The Science of Physics
 1.2
Distance, Time, and Measurement
 1.3
Speed
1.3 Investigation: Experiments and Variables
Key Questions:
How do you design a
valid experiment?
Objectives:

Set up an experiment.
Explain the difference between control and experimental
variables.
 Discuss why conducting multiple experimental trials is
better than gathering only one set of data.

Speed

To understand the concept of speed, use the
bicycle example below:
Speed
Think about two questions:

How many meters does each bicycle move each
second?
2. Does the bicycle move the same number of
meters every second?
1.
Speed

Think about two questions:
1.
How many meters does each bicycle move each second?
—
2.
Ans: Bike #1= 1 meter , Bike #2 = 3 meters
Does each bicycle move the same number of meters
every second?
—
Ans: yes
Speed
 The
speed of a bicycle is the distance it travels
divided by the time it takes.
 At
1 m/s, bike #1 travels 1 meter per second.
 At
3 m/s, bike #2 travels 3 meters per second.
 Constant
speed means the same distance is traveled
every second.
 Each
bicycle is moving at constant speed, but their
speeds are not the same.
Calculating speed
 To
calculate the speed of
an object, you need to
know two things:
— the distance traveled by
the object, and
— the time it took to travel
the distance.
Calculating speed
 Speed
is also a ratio of distance to time.
 The
word per means “for every” or “for each.”
 You
can also think of per as meaning “divided by.”
Relationships between variables
 There
are three ways to arrange the letters, or
variables, that relate distance, time, and speed.
 You
can solve for any one of the three variables if
you know the other two.
How to solve physics problems

Learning physics will make you a better problem solver, a
skill is important in all careers.

The technique for solving problems in this book has four
steps:
1. Identify what the problem is asking, and what variables
need to be in the answer.
2. Identify the information you are given.
3. Identify any relationships between the information you are
asked to find and what is given.
4. Combine the relationships with what you know and what
you are to find.
Calculating speed
An airplane flies 450 meters in 3 seconds.
What is its speed in meters per second?
1.
Looking for: … the speed in meters/second.
2.
Given: …the distance (450 m) and the time (3 s)
3.
Relationships: Use a version of the speed
equation:
v=d÷t
4.
Solution: v = 450 m ÷ 3 s = 150 m/s
Scientific Method and Serendipity

Serendipity is a term used to
describe an event that
happens by accident and
results in an unexpected
discovery.

It is through education and a
strong sense of curiosity,
tempered with a bit of
creativity (and yes, sometimes
a little luck), that people can
make great scientific
discoveries.