Chapter 1 - The Science of PhysicsSection 1.1 - What is Physics?

What is Physics?Physics is the study of the physical world

Goal:To use a small number of basic concepts, equations, and assumptions to describe the physical world

Physics is EVERYWHERE!!

The atom and its partsBehavior of submicroscopic particles

Quantum mechanics

Particle collisions, particle accelerators, nuclear energy

Particles moving at any speed, including very high speeds

Relativity

Electrical charge, circuitry, permanent magnets . . .

Electricity, magnetism, and light

Electromagnetism

Mirrors, lenses, color, astronomy

LightOptics

Springs, pendulums, soundSpecific types of repetitive motions

Vibrations and wave phenomena

Melting and freezing processes, engines . . .

Heat and temperatureThermodynamics

Falling objects, friction, weight, spinning objects

Motion and its causesMechanics

ExamplesSubjectsName

Areas within Physics

Topics of Physics

Topics of Physics

The scientific Method

SCIENTIFICALLYPROVENX

Make observationsAnd collect data thatLead to a question

Formulate Hypothesis

Test Hypothesis: Experiments

Interpret Results, and revise the hypothesis if

necessary

State Conclusions in a form that can be

evaluated by others

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The Scientific MethodA police investigator comes to the scene of an accident

Observation?Hypothesis?

Experiments/tests?Interpret/revise hypothesis?

Conclusions?

Models describe only a part of reality

a replica or description designed to show the structure or workings of an object, system, or concept

Physicists decide which parts are important and which aren’t

Physicists use Models

Physicists use Models

E.g. Basketball

System: a set of items or interactions considered a distinct physical entity for the purpose of study.

In the basketball example you are studying the ball and its motion

Other factors such as color, size, spin, aren’t considered in the model

Physicists use ModelsReview:

A Model describes a part of reality

The system is what you are studying

Galileo’s Hypothesis

What was the Question?

What was his hypothesis?

How did he test his hypothesis?

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Controlled ExperimentExperiment involving manipulation of a single variable or factor

In order to test a hypothesis, you must change one variable at a time

Chapter 1 - The Science of PhysicsSection 1.2 - Measurements in Experiments

Measurements in experiments

Dimension: tells us what physical quantity we are dealing with.

Three basic dimensions:

Length

Mass

Time

Units: tells us how much of that physical quantity we are talking about

SI standardsIn 1960, an agreement was made on seven base units

We will deal with only three

Second (s)Time

Kilogram (kg)Mass

Meter (m)Length

UnitDimension

Prefixes

SI uses prefixes to accommodate extremes

The distance between stars is approximately

100 000 000 000 000 000 m

The distance between atoms in a solid is approximately 0.000 000 001 m

Mr. Samuel can’t even say those numbers

You shouldn’t be expected to say them either

These numbers are expressed in powers of 10.

The distance between stars is approximately 1 x 1017

The distance between atoms is 1 x 10-9m

Prefixes

Power Prefix Abbreviation Power Prefix Abbreviation

10-18 atto- a 101 deka- da

10-15 femto- f 103 kilo- k

10-12 pico- p 106 mega- M

10-9 nano- n 109 giga- G

10-6 micro- 1012 tera- T

10-3 milli- m 1015 peta- P

10-2 centi- c 1018 exa- E

10-1 deci- d

Converting MeasurementsUse conversion factor that will cancel with the units you are

given to provide the units you need.

The units to which you are converting should usually be in the numerator.

It helps to cross out the units that cancel

Lets PRACTICE

Practice 1AA human hair is approximately 50 m in diameter. Express

this diameter in meters.

A typical radio wave has a period of 1 s. Express this period in seconds

A hydrogen atom has a diameter of about 10nm.

Express this diameter in meters.

Express this diameter in millimeters.

Express this diameter in micrometers.

The distance between the sun and the Earth is about 1.5 x 1011 m. Express this distance with an SI prefix and in kilometers.

The average mass of an automobile in the United States is about 1.440 x 106 g. Express this mass in kilograms

Accuracy vs PrecisionAccuracy is the closeness of measurements to the correct or

accepted value of the quantity measured.

Precision is the closeness of a set of measurements of the same quantity made in the same way.

Accuracy vs Precision

Accuracy vs Precision

Accuracy vs Precision

Accuracy vs Precision

Accuracy vs Precision

Accuracy vs Precision

Accuracy suggests that the experiment has accounted for all factors that might affect the system being studied

Precision lets us know that the experiment was done carefully in a controlled environment

Accuracy vs Precision

PrecisionPrecision describes the limitations of the measuring instrument

Significant FiguresSignificant figures are used in science to indicate precision

Includes all the digits actually measured (18 cm), plus one estimated digit

In the pencil example we can estimate that it is 0.2 cm past the 18 cm mark.

Because 18.2 cm is an estimate, the true value is between 18.15 cm and 18.25 cm.

Significant FiguresWhen last digit is a zero, it is impossible to tell how many significant figures there are.

If we say 230 mm, is it between 225 mm and 235 mm or is it between 229.5 mm and 230.5 mm.

We solve this by recording it in scientific notation by expressing it as a power of 10.

If there are 2 significant figures we write it as 2.3 x 102 cm.

If there are 3 significant figures we write it as 2.30 x 102 cm.

Rules for zeros

Rules for calculating sig figs

Rules for roundingCalculators do not pay attention to

significant figures

Chapter 1 - The Science of PhysicsSection 1.3 - The Language of Physics

Mathematics and physicsMathematical tools are used to analyze and summarize observations in physics

Tables, graphs and equations can make data easier to understand

Mathematics and Physics

(change in position in meters) = 4.9 x (time of fall in seconds)2

Mathematics and Physics

Physicists use mathematics to describe measured or predicted relationships. between physical quantities in a situation

Physicists use letters to describe specific quantities.

(delta) means “difference or change in”

(sigma) means “sum” or “total”.yt

Mathematics and Physics

Dimensional Analysis

Dimensional analysis can weed out invalid equations.

Dimensions can be treated as algebraic quantities.

The two sides of any given equation must have the same dimensions.

Dimensional AnalysisHow long does it take a car driving at 88 km/h to drive a distance of 725 km?

length

time×length=

length

timeor

88km1.0h

×75km=6. ×10km

1.0h

length ÷lengthtime

=length×time

lengthor

75km×1.0h88km

=8. h

Order-of-magnitude estimations

It is often useful to estimate an answer before solving the problem.

This can be done with an order-of-magnitude calculation - determining the power of 10 closest to the actual numerical value.

In the car example:10

3 km

102 km/h

=10h

The answer should be closer to 10 than to 1 or 100

8.2 h is the correct answer and fits this range