ch 1 Holt physics for science and agriculture

Copyright © by Holt, Rinehart and Winston. All rights reserved.
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The Science of Physics
Chapter 1
Table of Contents
Section 1 What Is Physics?
Section 2 Measurements in Experiments
Section 3 The Language of Physics

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Chapter 1
Objectives
• Identify activities and fields that involve the major
areas within physics.
• Describe the processes of the scientific method.
• Describe the role of models and diagrams in physics.

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Chapter 1
The Branches of Physics

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Chapter 1
Physics
• The goal of physics is to use a small number of
basic concepts, equations, and assumptions to
describe the physical world.
• These physics principles can then be used to make
predictions about a broad range of phenomena.
• Physics discoveries often turn out to have
unexpected practical applications, and advances in
technology can in turn lead to new physics
discoveries.

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Chapter 1
Physics and Technology

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Chapter 1
The Scientific Method
• There is no single
procedure that scientists
follow in their work.
However, there are
certain steps common to
all good scientific
investigations.
• These steps are called
the scientific method.

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Chapter 1
Models
• Physics uses models that describe phenomena.
• A model is a pattern, plan, representation, or
description designed to show the structure or
workings of an object, system, or concept.
• A set of particles or interacting components
considered to be a distinct physical entity for the
purpose of study is called a system.

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Chapter 1
Hypotheses
• Models help scientists develop hypotheses.
• A hypothesis is an explanation that is based on prior
scientific research or observations and that can be
tested.
• The process of simplifying and modeling a situation
can help you determine the relevant variables and
identify a hypothesis for testing.

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Chapter 1
Hypotheses, continued
Galileo modeled the behavior of falling objects in
order to develop a hypothesis about how objects fall.
If heavier objects fell faster
than slower ones,would two
bricks of different masses
tied together fall slower (b)
or faster (c) than the heavy
brick alone (a)? Because of
this contradiction, Galileo
hypothesized instead that all
objects fall at the same rate,
as in (d).

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Chapter 1
Controlled Experiments
• A hypothesis must be tested in a controlled
experiment.
• A controlled experiment tests only one factor at a
time by using a comparison of a control group with
an experimental group.

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Section 2 Measurements in
Experiments
Chapter 1
Objectives
• List basic SI units and the quantities they describe.
• Convert measurements into scientific notation.
• Distinguish between accuracy and precision.
• Use significant figures in measurements and
calculations.

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Experiments
Chapter 1
Numbers as Measurements
• In SI, the standard measurement system for science,
there are seven base units.
• Each base unit describes a single dimension, such
as length, mass, or time.
• The units of length, mass, and time are the meter
(m), kilogram (kg), and second (s), respectively.
• Derived units are formed by combining the seven
base units with multiplication or division. For
example, speeds are typically expressed in units of
meters per second (m/s).

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Chapter 1
SI Standards
Experiments

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Experiments
Chapter 1
SI Prefixes
In SI, units are
combined with
prefixes that
symbolize
certain powers
of 10. The most
common
prefixes and
their symbols
are shown in the
table.

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Experiments
Chapter 1
Dimensions and Units
• Measurements of physical quantities must be
expressed in units that match the dimensions of that
quantity.
• In addition to having the correct dimension,
measurements used in calculations should also have
the same units.
For example, when
determining area by
multiplying length and width,
be sure the measurements
are expressed in the same
units.

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Experiments
Chapter 1
Sample Problem
A typical bacterium has a mass of about 2.0 fg. Express
this measurement in terms of grams and kilograms.
Given:
mass = 2.0 fg
Unknown:
mass = ? g mass = ? kg

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Experiments
Chapter 1
Sample Problem, continued
Build conversion factors from the relationships given in
Table 3 of the textbook. Two possibilities are:
Only the first one will cancel the units of femtograms to
give units of grams.
–15
–15
1 10 g 1 fg
and
1 fg 1 10 g


–15
–15
1 10 g
(2.0 fg) = 2.0 10 g
1 fg
 


 
 

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Experiments
Chapter 1
Sample Problem, continued
Take the previous answer, and use a similar process to
cancel the units of grams to give units of kilograms.
–15 –18
3
1 kg
(2.0 10 g) = 2.0 10 kg
1 10 g
 
 
 

 

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Experiments
Chapter 1
Accuracy and Precision
• Accuracy is a description of how close a
measurement is to the correct or accepted value of
the quantity measured.
• Precision is the degree of exactness of a
measurement.
• A numeric measure of confidence in a measurement
or result is known as uncertainty. A lower uncertainty
indicates greater confidence.

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Experiments
Chapter 1
Significant Figures
• It is important to record the precision of your
measurements so that other people can understand
and interpret your results.
• A common convention used in science to indicate
precision is known as significant figures.
• Significant figures are those digits in a
measurement that are known with certainty plus the
first digit that is uncertain.

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Experiments
Chapter 1
Significant Figures, continued
Even though this ruler is
marked in only centimeters
and half-centimeters, if you
estimate, you can use it to
report measurements to a
precision of a millimeter.

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Chapter 1
Rules for Determining Significant Zeros
Experiments

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Chapter 1
Rules for Calculating with Significant Figures
Experiments

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Chapter 1
Rules for Rounding in Calculations
Experiments

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Section 3 The Language of
Physics
Chapter 1
Objectives
• Interpret data in tables and graphs, and recognize
equations that summarize data.
• Distinguish between conventions for abbreviating
units and quantities.
• Use dimensional analysis to check the validity of
equations.
• Perform order-of-magnitude calculations.

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Chapter 1
Mathematics and Physics
• Tables, graphs, and equations can make data
easier to understand.
• For example, consider an experiment to test Galileo’s
hypothesis that all objects fall at the same rate in the
absence of air resistance.
– In this experiment, a table-tennis ball and a golf ball are
dropped in a vacuum.
– The results are recorded as a set of numbers corresponding
to the times of the fall and the distance each ball falls.
– A convenient way to organize the data is to form a table,
as shown on the next slide.
Physics

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Chapter 1
Data from Dropped-Ball Experiment
Physics
A clear trend can be seen in the data. The more time that
passes after each ball is dropped, the farther the ball falls.

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Chapter 1
Graph from Dropped-Ball Experiment
Physics
One method for analyzing the data is to construct a
graph of the distance the balls have fallen versus the
elapsed time since they were released.
The shape of the
graph provides
information about
the relationship
between time and
distance.
Y=ax+b
Y=ax^2+bx+c

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Chapter 1
Physics Equations
• Physicists use equations to describe measured or
predicted relationships between physical quantities.
• Variables and other specific quantities are abbreviated
with letters that are boldfaced or italicized.
• Units are abbreviated with regular letters, sometimes
called roman letters.
• Two tools for evaluating physics equations are
dimensional analysis and order-of-magnitude
estimates.
Physics

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Chapter 1
Equation from Dropped-Ball Experiment
• We can use the following equation to describe the relationship
between the variables in the dropped-ball experiment:
(change in position in meters) = 4.9  (time in seconds)2
• With symbols, the word equation above can be written as follows:
Dy = 4.9(Dt)2
• The Greek letter D (delta) means “change in.” The abbreviation
Dy indicates the vertical change in a ball’s position from its
starting point, and Dt indicates the time elapsed.
• This equation allows you to reproduce the graph and make
predictions about the change in position for any time.
Physics

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Multiple Choice
1. What area of physics deals with the subjects
of heat and temperature?
A. mechanics
B. thermodynamics
C. electrodynamics
D. quantum mechanics
Standardized Test Prep
Chapter 1

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Multiple Choice, continued
3. What term describes a set of particles or interacting
components considered to be a distinct physical
entity for the purpose of study?
A. system
B. model
C. hypothesis
D. controlled experiment
Chapter 1

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4. What is the SI base unit for length?
F. inch
G. foot
H. meter
J. kilometer
Chapter 1

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Chapter 1
5. A light-year (ly) is a unit of distance defined as the
distance light travels in one year.Numerically, 1 ly =
9 500 000 000 000 km. How many meters are in a
light-year?
A. 9.5  1010 m
B. 9.5  1012 m
C. 9.5  1015 m
D. 9.5  1018 m

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5. A light-year (ly) is a unit of distance defined as the
distance light travels in one year.Numerically, 1 ly =
9 500 000 000 000 km. How many meters are in a
light-year?
A. 9.5  1010 m
B. 9.5  1012 m
C. 9.5  1015 m
D. 9.5  1018 m
Chapter 1

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6. If you do not keep your line of sight directly over a
length measurement, how will your measurement
most likely be affected?
F. Your measurement will be less precise.
G. Your measurement will be less accurate.
H. Your measurement will have fewer significant
figures.
J. Your measurement will suffer from instrument
error.
Chapter 1

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7. If you measured the length of a pencil by using the
meterstick shown in the figure and you report your
measurement in centimeters, how many significant
figures should your reported measurement have?
A. one
B. two
C. three
D. four
Chapter 1

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8. A room is measured to be 3.6 m by 5.8 m.What is the
area of the room? (Keep significant figures in mind.)
F. 20.88 m2
G. 2  101 m2
H. 2.0  101 m2
J. 21 m2
Chapter 1

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9. What technique can help you determine the power of
10 closest to the actual numerical value of a
quantity?
A. rounding
B. order-of-magnitude estimation
C. dimensional analysis
D. graphical analysis
Chapter 1

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10. Which of the following statements is true of any
valid physical equation?
F. Both sides have the same dimensions.
G. Both sides have the same variables.
H. There are variables but no numbers.
J. There are numbers but no variables.
Chapter 1

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The graph shows the relationship between time and
distance for a ball dropped vertically from rest. Use
the graph to answer questions 11–12.
Chapter 1
11. About how far has the
ball fallen after 0.20 s?
A. 5.00 cm
B. 10.00 cm
C. 20.00 cm
D. 30.00 cm

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Chapter 1
12.Which statement best describes the relationship
between the variables?
F. For equal time intervals, the
change in position is increasing.
G. For equal time intervals, the
change in position is decreasing.
H. For equal time intervals, the
change in position is constant.
J. There is no clear relationship
between time and change in
position.

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Short Response
Chapter 1
13. Determine the number of significant figures
in each of the following measurements.
A. 0.0057 kg
B. 5.70 g
C. 6070 m
D. 6.070  103 m

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Short Response
Chapter 1
13. Determine the number of significant figures
in each of the following measurements.
A. 0.0057 kg
B. 5.70 g
C. 6070 m
D. 6.070  103 m
Answers:
A. 2; B. 3; C. 3; D. 4

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Short Response, continued
Chapter 1
14. Calculate the following sum, and express the
answer in meters. Follow the rules for significant
figures.
(25.873 km) + (1024 m) + (3.0  102 cm)

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Chapter 1
14. Calculate the following sum, and express the
answer in meters. Follow the rules for significant
figures.
(25.873 km) + (1024 m) + (3.0  102 cm)
Answer: 26 897 m

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Chapter 1
15. Demonstrate how dimensional analysis can be used
to find the dimensions that result from dividing
distance by speed.

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Chapter 1
15. Demonstrate how dimensional analysis can be used
to find the dimensions that result from dividing
distance by speed.
Answer:
distance distance time
distance = time
time distance

 

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Extended Response
Chapter 1
16. You have decided to test the effects of four different
garden fertilizers by applying them to four separate
rows of vegetables. What factors should you
control? How could you measure the results?

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Extended Response
Chapter 1
16. You have decided to test the effects of four different
garden fertilizers by applying them to four separate
rows of vegetables. What factors should you
control? How could you measure the results?
Sample answer: Because the type of fertilizer is the
variable being tested, all other factors should be
controlled, including the type of vegetable, the
amount of water, and the amount of sunshine. A fifth
row with no fertilizer could be used as the control
group. Results could be measured by size, quantity,
appearance, and taste.

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Extended Response, continued
Chapter 1
17. In a paragraph, describe how you could estimate
the number of blades of grass on a football field.

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Extended Response, continued
Chapter 1
17. In a paragraph, describe how you could estimate
the number of blades of grass on a football field.
Answer: Paragraphs should describe a process similar
to the following: First, you could count the number of
blades of grass in a small area, such as a 10 cm by
10 cm square. You would round this to the nearest
order of magnitude, then multiply by the number of
such squares along the length of the field, and then
multiply again by the approximate number of such
squares along the width of the field.

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