The Science of Physics Learn about the branches of physics, the scientific method, physics models...
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Transcript of The Science of Physics Learn about the branches of physics, the scientific method, physics models...
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..