The Science of PhysicsThe Science of PhysicsLearn about the branches of physics, the scientific method, physics models and tools

What is physics?What is physics?Most think physics is hard

◦Deals with the tiny atom (Nuclear physicist)

◦Or the Universe (Astrophysicist)Actually everything you perceive is

physics◦Temperature◦Size◦Motion◦Position◦Shape◦Color, etc

Areas of PhysicsAreas of PhysicsName Subjects Example

Mechanics Motion and its causes, interactions between objects

Falling, friction, weight, spinning

Thermodynamics Heat and temperature

Melting, freezing, engines, refrigerators

Vibrations and Waves

Specific types of repetitive motions

Springs, pendulums, sound

Optics Light Mirrors, lenses, color, astronomy

Electromagnetism Electricity, magnetism, and light

Electrical charge, circuitry, magnets and electromagnets

Relativity Particles moving at any speed, including very high speeds

Particle collisions, particle accelerators, nuclear energy

Quantum mechanics

Behavior of submicroscopic particles

The atoms and its parts

The Scientific MethodThe Scientific MethodProblemObservationHypothesisExperimentConclusion

ModelsModelsUsed to explain most

fundamental features of a phenomena

Successful in describing natureMust simplify to a SYSTEM

◦Leave out irrelevant information◦Isolate the object you are studying

HypothesisHypothesisReasonable explanation for an

observationTestableSimplify the model to make a

hypothesis

Galileo’s “Thought Galileo’s “Thought Experiment”Experiment”Hypothesis - Objects fall at the same

rate:A. Heavy brick and light brick - it was

assumed that the heavy would fall fasterB. Heavy brick tied to light brick – Heavy

brick would speed up the light one, the light one would slow-down the heavy

C. Heavy brick tied to light brick – Combined weight was more, therefore it should fall faster

D. Therefore – all things fall at same rate

Challenges to Galileo's Challenges to Galileo's HypothesisHypothesisTime measuring devices where

not too accurateTo slow down the experiment he

used ramps◦The steeper the ramp, the closer it

was to freefall◦Used ball of different weight, same

size on one ramp at a timeControlled experiments – change

one variable at a time

Ramp Experiments

The Four ForcesThe Four ForcesForce – Agent of Change

◦Gravitational acts between all particles Weakest force Only attraction Unlimited range

◦Electromagnetic Short range interatomic Causes contact forces between objects Unlimited range Has attraction and repulsion

Four ForcesFour Forces

◦Strong Force – Force that hold together the parts of the atom – quarks Very strong Very short range

◦Weak – Force that causes parts of atoms to break apart Second weakest Very short range

DimensionsDimensionsPhysical quantity that is directly

measurableBasic:

◦Length◦Mass◦Time◦Temperature◦Electric current◦Amount of substance◦Luminous intensity

All other dimensions are derived from the basic – force, velocity, energy, volume, etc.

SI – International Standard SI – International Standard measurement for sciencemeasurement for scienceAgreed on in 1960Describe the standard units

◦Meter – the distance traveled by light in a vacuum in 3.33564095 x 10-9

◦Kilogram – mass of a specific platinum-iridium alloy cylinder

◦Second – 9 132 631 770 times the period of a radio wave emitted from a cesium-133 atom

SI Base UnitsSI Base UnitsBase Quantity Base unit Symbol

Length Meter M

Mass Kilogram kg

Time Second S

Temperature Kelvin K

Amount of substance

Mole mol

Electric current Ampere A

Luminous intensity Candela cd

Metric SystemMetric SystemPrefix Symbo

lMultiplier Scientif

ic Notation

Example

femto- f 0.0000000000000001

10 -15 Femtosecond (fs)

pico- p 0.000000000001 10 -12 picometer (pm)

nano- n 0.000000001 10 -9 Nanobrain

micro- µ 0.000001 10 -6 Microgram (µg)

milli- m 0.001 10 -3 Milliamps (mA)

centi- c 0.01 10 -2 Centimeter (cm)

deci- d 0.1 10 -1 Deciliter (dL)

kilo- k 1000 10 3 Kilometer (km)

mega- M 1 000 000 10 6 Meganerd

giga- G 1 000 000 000 10 9 Gigameter (Gm)

tera- T 1 000 000 000 000

10 12 Terahertz (THz)

Powers of Tenhttp://micro.magnet.f

su.edu/primer/java/scienceopticsu/powersof10/

Converting within the SI system is SO EASY – all you do is multiple or divide by powers of ten!!!

Need to know◦ Prefixes◦ Meanings

Dimensional AnalysisDimensional AnalysisUse units to check your workNeed formulas to solve physics

problemsTreat the units like algebraic

quantitiesUseful in conversion factors too

Significant FiguresSignificant FiguresMeasured values plus one

estimated numberDepends on the instrument in

which you use to measure Arithmetic with Sig Figs

◦Add or Subtract – round to the least-precise decimal place

◦Multiple or Divide – round to the number of Sig Figs in the least-precise value

Calculators do not track Sig

Figs!!

Accuracy and PrecisionAccuracy and PrecisionNo measurement is perfectMean different things in

science◦Accuracy – How close to the exact

value Method error Instrumental error

◦Precision – Degree of exactness of a measurement Due to limitations of the instrument Can be improved by making a

reasonable estimate between the lines

Mathematics and PhysicsMathematics and PhysicsMathematic relations help us to

predict new situationsTools

◦Tables – organize data◦Graphs – display data◦Equations – describe relations

between variables Use letters (English and Greek) to

describe a quantity

Graphing DataGraphing DataIdentify variables

◦Independent – factor that changes or is manipulated during the experiment (x axis) Time is a common independent

◦Dependent – factor that depends on the independent variable (y axis)

Ruths’ Rules of Plotting Line Ruths’ Rules of Plotting Line GraphsGraphs1. Identify independent (x axis) and

dependent (y axis) variables2. Determine range of independent

variable3. Decide whether the origin (0,0) is a

valid data point4. Spread the data out as much as

possible5. Let each division on the graph paper

stand for a convenient unit (2, 5, 10, etc)

Plotting Line GraphsPlotting Line Graphs6. Number and label the horizontal axis –

include units7. Repeat steps 2-6 for dependent

variable8. Plot the data points on the graph -

circle9. Draw the best-fit straight line or smooth

curve that passes through as many data points as possible (eye-balling)

- No line segments (lightning bolts)- Graphing calculators use least-square

techniques

Plotting Line GraphsPlotting Line Graphs

10. Give the graph a title that clearly tells what the graph represents

Relationships on GraphsRelationships on GraphsThree most common:

◦Linear◦Quadratic◦Inverse

Linear RelationshipsLinear RelationshipsBest-fit line is a straight lineDependent variable varies

linearly with the independent variable

Equation: y = mx + b◦b – y-intercept◦m – slope

Linear Relations - SlopeLinear Relations - SlopeSlope is the ratio of vertical

change to horizontal changeSlope = rise = Δy = m

run Δx ◦ Negative slope – y gets smaller as x gets

larger◦ Positive slope – y gets larger as x gets

larger

Linear Graph

Nonlinear RelationshipsNonlinear RelationshipsCurved line graphsMost common:

◦Quadratic◦Inverse

Others◦Sinusoids – cyclical patterns (sine,

cosine)◦Exponential – logrhymic

QuadraticQuadraticy = ax² + bx + cComputers and

graphing calculators can easily solve for a, b, and c

Use the quadratic formula to solve for x (two solutions)

Produces a parabola graph

ParabolaParabola

Inverse RelationshipInverse Relationshipy = a/xResults in a

hyperbola

Predicting valuesPredicting valuesOnce a relationship is discovered,

it can be used for predictionsModels

◦Used to predict Solar flares How a device will react to a change in

voltage How magnetic fields will effect a medical

instrument Etc..