An Introduction to Physics

Honors Physics

Wilmington HS

2011-2012

What IS physics?

• Physics is the most fundamental science– Physics describes the nature

of things such as force, motion, energy, matter, heat, sound, light, and atomic and nuclei compositions.

• Physics explains all phenomena found in the other sciences and is the foundation for all life and matter

Why study physics?

• Physics is the study of the fundamental laws of nature. It is the science that regulates and describes all of the other sciences!!!

• Pythagoras ancient Greece • Aristotle “The Natural Sciences”• Galileo 16th century• Newton 17th century• Modern Physics 19th century

Sir Isaac Newton,

considered by many to be the

“Father of Physics”.

Scientific Method

Measurement:a quantitative observation

Hypothesis: a very tentative, possible

answer or an educated guess

Experiment: an observation of

natural phenomena

carried out in a controlled manner

Theory: a well-tested explanation of a broad segment of naturalphenomena

Scientific revolutions of the 1600s were due primarily to an adoptionof the scientific methodby Galileo, Newton, andBoyle.

Ockham’s Razor: Inchoosing between two seemingly valid explanationsof a particular phenomenon, the simpler and more general explanation is typicallypreferred. Simplicity is beauty in science, and often proves valid!

Science, Technology, and Society

• Science– A method of answering

THEORETICAL questions– Has to do with discovering

facts and relationships between observable happenings in nature and with established theories

– Usually driven simply by the urge to know and discover

– In an ideal world, science is free of belief, values, and current pop trends

• But is that always the case?

Technology

• Method of solving practical problems

• Has to do with tools, techniques, and procedures for putting the findings of science to use.– EX: Science was responsible for

discovering penicillin, but technology was responsible for finding a way to manufacture and distribute it.

• Technology designs, creates, or builds something for human joy or the betterment of life.

• Is improper technology responsible for widespread pollution, cultural decay, and resource depletion?

Chapter 1:Introduction

to Physics

Standards of length, mass, and time, measurement, uncertainty,

and mathematics

The three fundamental quantities

• Length (L), mass (M), and time (T)– All other physical

quantities can be constructed from these three

• Example: the unit for acceleration is m/s2

S.I. Unit for length, [L]

• The “meter”– Abbreviated m– The meter is defined as

the distance traveled by light in a vacuum during a time interval of 1/299,792,458th second

– The speed of light is 299,792,458 m/s

Saturn, as seen during last year’s lunar eclipse through telescope

Approximate values of some measured lengths

Distance from earth to most remote known star

1 x 1026 meters

Distance from Earth to Andromeda galaxy

2 x 1022 m

One light year 9 x 1015 m

Orbit radius of Earth about sun 2 x 1011 m

Mean distance from Earth to moon 4 x 108 m

Length of a football field 9 x 101 m

Length of a housefly 5 x 10-3 m

Size of smallest dust particles 1 x 10-4 m

Size of most living cells 1 x 10-5 m

Diameter of hydrogen atom 1 x 10-10 m

Diameter of atomic nucleus 1 x 10-14 m

Diameter of a proton 1 x 10-15 m

SI Unit for Mass, [M]• Mass: the kilogram

– One kilogram is the mass of a particular platinum-iridium cylinder kept at the International Bureau of Weights and Standards, Sèvres, France.

– One kilogram is roughly 2.2 lbs.

Approximate values of some masses

Observable Universe 1 x 1052 kilograms

Earth 6 x 1024 kilograms

Shark 1 x 102 kilograms

Human 7 x 101 kilograms

Mosquito 1 x 10-5 kilograms

Bacterium 1 x 10-15 kilograms

Hydrogen Atom 2 x 10-27 kilograms

Electron 9 x 10-31 kilograms

S.I. Unit for time, [T]

• The “second”– Abbreviated s– The second is now

defined as 9,192,631,700 times the period of oscillation of radiation from the cesium atom

Approximate values of some time intervals

Age of Universe 5 x 1017 seconds

Age of the Earth 1 x 1017 seconds

Average age of College Student 6 x 108 seconds

One year 3 x 107 seconds

Time between normal heartbeats 8 x 10-1 seconds

Time required for one complete vibration of a sound wave

1 x 10-3 seconds

Time required for one complete vibration of a light wave

2 x 10-15 seconds

Duration of a nuclear collision 1 x 10-22 seconds

Important prefixes used in scientific notation

Power Prefix Abbreviation10-15 Femto- Lower case f

10-12 Pico- Lower case p

10-9 Nano- Lower case n

10-6 Micro- μ

10-3 Milli- Lower case m

10-2 Centi- Lower case c

10-1 Deci- Lower case d

101 Deka- Lower case da

103 Kilo- Lower case k

106 Mega- Upper case M

109 Giga- Upper case G

1012 Tera- Upper case T

Converting units in the SI system• When I was in High School, Mrs. Heck taught me “Kathy Hugs Dirty

Boys During Class Monday”. Since then, I’ve developed my own way to remember the central units.

Kind Mrs.Heck Decked BobDylan in Chemistry class Monday

***The names “Bette Davis” (actress), “Bob (Robert) DiNero” (actor), and “Bob Dole” (former presidential candidate) could also be used. I chose Bob Dylan because he was an awesome song writer, and who doesn’t love the song “The Hurricane” or “Knockin’ on Heaven’s Door”?

Dimensional Analysis

• Dimension– The physical nature of a quantity

• Dimensional analysis treats units as algebraic quantities– Quantities can only be added or subtracted if

they have the SAME UNITS!– You can multiply or divide any units

S.I. units for specific quantities

• AREA (L2) is measured in m2

• VOLUME (L3) is measured in m3

• VELOCITY (L/T) is measured in m/s

• ACCELERATION (L / T2) is measured in m/s2

Dimensional Analysis• Any valid physical formula must be dimensionally

consistent – each term must have the same dimensions

Uncertainty and Significant Figures• No physical quantity can be

determined with perfect accuracy because our physical senses are limited

• Accuracy of measurement depends on the sensitivity of the apparatus, skill of the measurer, and the number of times the measurement is repeated

• A measurement is MEANINGLESS without consideration to the error involved

Significant figures

• A reliably known digit– In this class, you will ALWAYS use

significant figures. You will lose half of your total points per problem if the incorrect significant figures are used

• Zeroes can be tricky…– Examples

General Rules for Sig Figs

• General rules– When multiplying or dividing, take the lowest

number of significant figures given in the problem/measurement

• 4.5 cm x 2.0000 cm = 9.0 cm

(2 sf) (5 sf) (2 sf)

– When adding or subtracting, take the smallest number of digits past the decimal

• 3.105 + 1.00 – 2.00000 = 2.105 = 2.11

(3 pd) (2 pd) (5 pd) (2 pd)

Unit conversions

• Sometimes it is necessary to convert units from one to another (trust me on this…you do these conversions all of your life)

• Helpful units• One mile = 1609 m = 1.609 km• 1 meter = 39.37 in = 3.281 ft• 1 foot = 0.3048 m = 30.48 cm• 1 inch = 0.0254 m = 2.54 cm

Estimates and orders of magnitude

• When getting an exact answer is impossible, we use approximations– You may not know a car

is going 70 mph, but you may be able to approximate it to 65 based on the speed limit, for instance.

• Simply find the power of 10 that is closest to the value

Coordinate systems

• Many aspects of physics deal with location in space

• Coordinate systems– Reference point “O” is the origin– Specified axes, or directions, with proper units– We will normally use Cartesian coordinate systems

(2-d rectangles)– We will also use plane polar coordinates that

reference a point by the ordered pair (r, θ)

Cartesian Coordinate System

Plane Polar Coordinate System

Trigonometry• Applied to right triangles

–Sinθ = (o / h) = y / r

–Cosθ = (a / h) = x / r

–Tanθ = (o / a) = y / x

• Pythagorean Theorem• r2 = x2 + y2

Scalars and Vectors

• Scalar – a numerical value that is directionless. • May be positive or negative. • Examples: distance, temperature, speed, height, mass

• Vector – a quantity with both magnitude and direction.

• Examples: displacement (e.g., 10 feet north), velocity, acceleration, force, magnetic field, weight

• The difference between these two quantities will be important as the course progresses!

The Problem-Solving Strategy• 1) Conceptual Grasp

• What knowledge is relevant to the situation?– What are the given conditions and assumptions that must be made?

• 2) Devise a plan• Draw a picture if you haven’t already done so!!• What steps are necessary to solve the problem?• Can you imagine or visualize the conditions of the problem?

• 3) Solve the problem• Mathematically manipulate your problem-solving plan• Keep your work neat and organized so that you don’t get lost

• 4) Check your answer for plausibility• Comparison analysis?• Dimensional analysis?• Does your answer make sense given the circumstances?