1 fisica 1 per biotecnologie introduzione lun h 10:30 mer h 10:30 gio h 10:30 alessandro de angelis...
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Fisica 1 per BiotecnologieIntroduzione
Lun h 10:30Mer h 10:30 Gio h 10:30
Alessandro De Angelis E-mail [email protected] il mercoledì, 8:30-9:30
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Grantecan
MAGIC and its Control House
Telescopio Nazionale Galileo
MAGIC
La Palma, IAC28° North, 18° West
MAGIC
MAGIC
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www.fisica.uniud.it/~deangeli/biotec Obiettivi: Scopo del corso è di fornire gli elementi di base della fisica
generale.
Struttura: Il corso si svolge nel I periodo del I anno, con 22 lezioni distribuite in tre unità di 90 minuti ogni settimana. Nella pagina Web del corso e' pubblicata una versione aggiornata della struttura dettagliata delle lezioni (vedi tabella a pie' di pagina).
Programma: Unità di misura. Cinematica. Forze in natura: gravitazione, elettromagnetismo. Dinamica. Energia. Oscillazioni; cenni sul moto ondulatorio e sulle onde elettromagnetiche.
Testo: Serway e Jewett - Principi di Fisica vol. 1, ultima edizione, EdiSES; appunti di lezione (che non sostituiscono il testo). Gli appunti di lezione e una selezione dei compiti degli anni precedenti sono reperibili nel sito del materiale didattico.
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www.fisica.uniud.it/~deangeli/biotec Titolare: Il titolare del corso si chiama Alessandro De Angelis. Riceve
nell'orario riportato su SINDY, o su appuntamento scrivendo a [email protected]. Melisa Rossi contribuisce al corso.
Valutazione: Nella sessione d'esame (due appelli) che segue il corso il voto proposto e' dato dal voto di un accertamento finale (valutato fino a 30 punti) cui viene aggiunto un bonus da 0 a 6 punti basato sulla valutazione dei compiti per casa. Lo studente che abbia superato la prova riportando un voto complessivo non inferiore a 18/30 supera l'esame. Nelle sessioni successive (un appello a Luglio e uno a Settembre) l'esame consta di una prova scritta che include domande di teoria, o di un orale che include esercizi.
Consigli: Procurarsi il libro di testo ben prima dell'inizio del corso, magari sfogliarlo quando
non si sa che fare... Dare un'occhiata agli argomenti della lezione successiva (il programma lezione
per lezione e' dettagliato nella pagina Web del corso) Studiare regolarmente ogni giorno quanto svolto in classe e svolgere gli esercizi
relativi.
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(…)
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About Physics
Provides a quantitative understanding of
phenomena occurring in our universe
Based on experimental observations and
mathematical analysis
Used to develop theories that explain the
phenomena being studied and that relate to
other established theories
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What is Physics? Model Building
A model is a simplified substitution for the real problem that allows us to solve the problem in a relatively simple way Make predictions about the behavior of the system
The predictions will be based on interactions among the components and/or
Based on the interactions between the components and the environment
As long as the predictions of the model agree with the actual behavior of the real system, the model is valid
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Particle Model
The particle model allows the replacement of an extended object with a particle which has mass, but zero size
Two conditions for using the particle model are The size of the actual object is of no consequence in the
analysis of its motion Any internal processes occurring in the object are of no
consequence in the analysis of its motion
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Theory and Experiments
Should complement each other When a discrepancy occurs, theory may be
modified Theory may apply to limited conditions
Example: Newtonian Mechanics is confined to objects traveling slowly with respect to the speed of light
Used to try to develop a more general theory
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Standards of Quantities
SI – Système International The system used in this course Consists of a system of definitions and standards to
describe fundamental physical quantities
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Time: second, s Historically defined as 1/86400 of a solar day Now defined in terms of the oscillation of radiation
from a cesium atom Some approximate time intervals, in s
Age of the Universe 5 1017
Since the fall of Roman Empire 5 1012
Your age 6 108
One year 107
One lecture 5 103
Time between two heartbeats 1
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Length: meter, m The “human-scale” definition: 1/10000000 of the
distance between the North Pole and the equator,
through Paris Length is now defined as the distance traveled by light
in a vacuum during a given time (~1/3 10-8 s) See table 1.1 for some examples of lengths
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Mass: kilogram, kg
The mass of a specific cylinder kept somewhere in Paris
See table 1.2 for masses of various objects
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Number Notation
Separation between units and decimals: dot (.) When writing out numbers with many digits,
spacing in groups of three will be used No commas, no dots
Examples: 25 100 5.123 456 789 12
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Reasonableness of Results
When solving problem, you need to check your answer to see if it seems reasonable How many molecules in a liter of milk?
Reviewing the tables of approximate values for length, mass, and time will help you test for reasonableness
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Systems of Measurements, SI Summary
SI System Almost universally used in science and industry Length is measured in meters (m) Time is measured in seconds (s) Mass is measured in kilograms (kg)
IT’S A LAW
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Prefixes Prefixes correspond to powers of 10 Each prefix has a specific name Each prefix has a specific abbreviation The prefixes can be used with any base units They are multipliers of the base unit Examples:
1 mm = 10-3 m 1 mg = 10-3 g
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Fundamental & Derived Quantities
In mechanics, three fundamental quantities are used Length Mass Time
Will also use derived quantities These are other quantities that can be expressed as a
mathematical combination of fundamental quantities Density is an example of a derived quantity; It is defined as
mass per unit volume
Units are kg/m3Vm
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Dimensional Analysis Technique to check the correctness of an equation or to assist
in deriving an equation. Dimension has a specific meaning – it denotes the physical nature of a quantity
Dimensions (length, mass, time, combinations) can be treated as algebraic quantities
Add, subtract, multiply, divide
Both sides of equation must have the same dimensions Dimensions are denoted with square brackets
Length – [L] Mass – [M] Time – [T]
Cannot give numerical factors: this is its limitation
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Dimensional Analysis, example
Given the equation: x = 1/2 a t2
Check dimensions on each side:
The T2’s cancel, leaving L for the dimensions of each side The equation is dimensionally correct There are no dimensions for the constant
][][][
][][ 2
2LT
T
LL
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Conversion of Units
When units are not consistent, you may need to convert to appropriate ones
Units can be treated like algebraic quantities that can cancel each other out
Always include units for every quantity, you can carry the units through the entire calculation
Multiply original value by a ratio equal to one The ratio is called a conversion factor
Example
km/h 361h
3600s
1000m
1km m/s 10
km/h ?m/s 10
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Order of Magnitude
Approximation based on a number of assumptions May need to modify assumptions if more precise results are
needed
Order of magnitude is the power of 10 that applies In order of magnitude calculations, the results are
reliable to within about a factor of 10
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Uncertainty in Measurements
There is uncertainty in every measurement, this uncertainty carries over through the calculations Need a technique to account for this uncertainty
We will use rules for significant figures to approximate the uncertainty in results of calculations
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Significant Figures A significant figure is one that is reliably known Zeros may or may not be significant
Those used to position the decimal point are not significant To remove ambiguity, use scientific notation
In a measurement, the significant figures include the first estimated digit
0.0075 m has 2 significant figures The leading zeroes are placeholders only Can write in scientific notation to show more clearly: 7.5 x 10-3 m for 2
significant figures 10.0 m has 3 significant figures
The decimal point gives information about the reliability of the measurement 1500 m is ambiguous
Use 1.5 x 103 m for 2 significant figures Use 1.50 x 103 m for 3 significant figures Use 1.500 x 103 m for 4 significant figures
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Operations with Significant Figures
When multiplying or dividing, the number of significant figures in the final answer is the same as the number of significant figures in the quantity having the lowest number of significant figures. Example: 25.57 m x 2.45 m = 62.6 m2
The 2.45 m limits your result to 3 significant figures
When adding or subtracting, the number of decimal places in the result should equal the smallest number of decimal places in any term in the sum. Example: 135 cm + 3.25 cm = 138 cm
The 135 cm limits your answer to the units decimal value
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Rounding
Last retained digit is increased by 1 if the last digit dropped is 5 or above
Last retained digit is remains as it is if the last digit dropped is less than 5
Saving rounding until the final result will help eliminate accumulation of errors
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Coordinate Systems
Used to describe the position of a point in space
Coordinate system consists of A fixed reference point called the origin Specific axes with scales and labels Instructions on how to label a point relative to the
origin and the axes
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Cartesian Coordinate System
Also called rectangular coordinate system
x- and y- axes intersect at the origin
Points are labeled (x,y)
3 coordinates (x,y,z) are enough to define the position of a particle in space
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Polar Coordinate System
Origin and reference line are noted
Point is distance r from the origin in the direction of angle , ccw from reference line
Points are labeled (r,)
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Polar to Cartesian Coordinates
Based on forming a right triangle from r and
x = r cos y = r sin
r is the hypotenuse and an angle
22 yxrxy
tan
Cartesian to Polar