The Science of Physics Learn about the branches of physics, the scientific method, physics models and tools

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 Physics NameSubjectsExample MechanicsMotion and its causes, interactions between objects Falling, friction, weight, spinning ThermodynamicsHeat and temperatureMelting, freezing, engines, refrigerators Vibrations and WavesSpecific types of repetitive motions Springs, pendulums, sound OpticsLightMirrors, lenses, color, astronomy ElectromagnetismElectricity, magnetism, and light Electrical charge, circuitry, magnets and electromagnets RelativityParticles moving at any speed, including very high speeds Particle collisions, particle accelerators, nuclear energy Quantum mechanicsBehavior of submicroscopic particles The atoms and its parts

The Scientific Method Problem Observation Hypothesis Experiment Conclusion

Models Used to explain most fundamental features of a phenomena Successful in describing nature Must simplify to a SYSTEM ◦ Leave out irrelevant information ◦ Isolate the object you are studying

Hypothesis Reasonable explanation for an observation Testable Simplify the model to make a hypothesis

Galileo’s “Thought Experiment” Hypothesis - Objects fall at the same rate: A.Heavy brick and light brick - it was assumed that the heavy would fall faster B.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 Hypothesis Time measuring devices where not too accurate To 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 time Controlled experiments – change one variable at a time

Ramp Experiments

The Four Forces Force – 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 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

Dimensions Physical quantity that is directly measurable Basic: ◦ 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 measurement for science Agreed on in 1960 Describe the standard units ◦ Meter – the distance traveled by light in a vacuum in x ◦ Kilogram – mass of a specific platinum-iridium alloy cylinder ◦ Second – times the period of a radio wave emitted from a cesium-133 atom

SI Base Units Base QuantityBase unitSymbol LengthMeterM MassKilogramkg TimeSecondS TemperatureKelvinK Amount of substanceMolemol Electric currentAmpereA Luminous intensityCandelacd

Metric System PrefixSymbolMultiplierScientific Notation Example femto-f Femtosecond (fs) pico-p picometer (pm) nano-n Nanobrain micro-µ Microgram (µg) milli-m Milliamps (mA) centi-c Centimeter (cm) deci-d Deciliter (dL) kilo-k Kilometer (km) mega-M Meganerd giga-G Gigameter (Gm) tera-T Terahertz (THz)

Powers of Ten u/primer/java/scienceoptic su/powersof10/ u/primer/java/scienceoptic su/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 Analysis Use units to check your work Need formulas to solve physics problems Treat the units like algebraic quantities Useful in conversion factors too

Significant Figures Measured values plus one estimated number Depends 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 Precision No measurement is perfect Mean 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 Physics Mathematic relations help us to predict new situations Tools ◦ Tables – organize data ◦ Graphs – display data ◦ Equations – describe relations between variables  Use letters (English and Greek) to describe a quantity

Graphing Data Identify 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 Graphs 1. Identify independent (x axis) and dependent (y axis) variables 2. Determine range of independent variable 3. Decide whether the origin (0,0) is a valid data point 4. Spread the data out as much as possible 5. Let each division on the graph paper stand for a convenient unit (2, 5, 10, etc)

Plotting Line Graphs 6. Number and label the horizontal axis – include units 7. Repeat steps 2-6 for dependent variable 8. Plot the data points on the graph - circle 9. 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 Graphs 10. Give the graph a title that clearly tells what the graph represents

Relationships on Graphs Three most common: ◦ Linear ◦ Quadratic ◦ Inverse

Linear Relationships Best-fit line is a straight line Dependent variable varies linearly with the independent variable Equation: y = mx + b ◦ b – y-intercept ◦ m – slope

Linear Relations - Slope Slope is the ratio of vertical change to horizontal change Slope = 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 Relationships Curved line graphs Most common: ◦ Quadratic ◦ Inverse Others ◦ Sinusoids – cyclical patterns (sine, cosine) ◦ Exponential – logrhymic

Quadratic y = ax² + bx + c Computers 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

Parabola

Inverse Relationship y = a/x Results in a hyperbola

Predicting values Once a relationship is discovered, it can be used for predictions Models ◦ Used to predict  Solar flares  How a device will react to a change in voltage  How magnetic fields will effect a medical instrument  Etc..