chapter 1 describe the processes of the scientific method. list basic si units and the quantities...

Chapter 1

Describe the processes of the scientific method.

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.

Interpret data in tables and graphs, and recognize equations that summarize data.

Use dimensional analysis to check the validity of equations.

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.

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.

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.

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.

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).

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.

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).

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.

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.

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

Build conversion factors from the relationships given inTable 3 of the textbook. Two possibilities are:

Only the first one will cancel the units of femtograms togive units of grams.

–15

–15

1 10 g 1 fg and

1 fg 1 10 g

–15–151 10 g

(2.0 fg) = 2.0 10 g1 fg

Take the previous answer, and use a similar process tocancel the units of grams to give units of kilograms.

–15 –183

1 kg(2.0 10 g) = 2.0 10 kg

1 10 g

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.

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.

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.

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.

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.

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:

y = 4.9(t)2

The Greek letter (delta) means “change in.” The abbreviation y indicates the vertical change in a ball’s position from its starting point, and t indicates the time elapsed.

This equation allows you to reproduce the graph and make predictions about the change in position for any time.

1. What area of physics deals with the subjects

of heat and temperature?

A. mechanicsB. thermodynamicsC. electrodynamicsD. quantum mechanics

Standardized Test PrepChapter 1


2. What area of physics deals with the behavior of

subatomic particles?

F. mechanics

G. thermodynamics

H. electrodynamics

J. quantum mechanics

3. What term describes a set of particles or interacting components considered to be a distinct physical entity for the purpose of study?

A. systemB. modelC. hypothesisD. controlled experiment


4. What is the SI base unit for length?

F. inchG. footH. meterJ. kilometer


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 mB. 9.5 1012 mC. 9.5 1015 mD. 9.5 1018 m


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.


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. oneB. twoC. threeD. four


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


9. What technique can help you determine the power of 10 closest to the actual numerical value of a quantity?

A. roundingB. order-of-magnitude estimationC. dimensional analysisD. graphical analysis


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.


The graph shows the relationship between time and distance for a ball dropped vertically from rest. Use the graph to answer questions 11–12.


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


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.

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


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


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)


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


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


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

Answer:


distance distance timedistance = time

time distance

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?


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.

17. In a paragraph, describe how you could estimate the number of blades of grass on a football field.


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.


Chapter 1Section 1 What Is Physics?

Section 2 Measurements in ExperimentsChapter 1

chapter 1 describe the processes of the scientific method. list basic si units and the quantities...

Documents

units of length

base units

units of meters

derived units

list basic si units

scientific method

scientific notation

goal of physics