Fisica 1 per Biotecnologie
Introduzione
Lun h 10:30
Mer h 10:30
Gio h 10:30
Alessandro De Angelis
E-mail [email protected]
Ricevo il mercoledì, 8:30-9:30 1
MAGIC
Telescopio Nazionale Galileo
La Palma, IAC
28° North, 18° West
Grantecan
MAGIC
MAGIC and its Control House
MAGIC
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www.fisica.uniud.it/~deangeli/biotec
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Obiettivi: Scopo del corso è di fornire gli elementi di base della fisica
generale.
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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).
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Programma: Unità di misura. Cinematica. Forze in natura: gravitazione,
elettromagnetismo. Dinamica. Energia. Oscillazioni; cenni sul moto
ondulatorio e sulle onde elettromagnetiche.
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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
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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.
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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.
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Consigli:
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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
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Provides a quantitative understanding of
phenomena occurring in our universe
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Based on experimental observations and
mathematical analysis
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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
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A model is a simplified substitution for the real
problem that allows us to solve the problem in a
relatively simple way
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Make predictions about the behavior of the system
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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
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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
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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
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Should complement each other
When a discrepancy occurs, theory may be
modified
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Theory may apply to limited conditions
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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
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SI – Système International
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The system used in this course
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Consists of a system of definitions and standards to
describe fundamental physical quantities
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Time: second, s
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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
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Age of the Universe
Since the fall of Roman Empire
Your age
One year
One lecture
Time between two heartbeats
5 1017
5 1012
6 108
p 107
5 103
1
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Length: meter, m
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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
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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
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Separation between units and decimals: dot (.)
When writing out numbers with many digits,
spacing in groups of three will be used
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No commas, no dots
Examples:
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25 100
5.123 456 789 12
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Reasonableness of Results
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When solving problem, you need to check your
answer to see if it seems reasonable
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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
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SI System
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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
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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:
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1 mm = 10-3 m
1 mg = 10-3 g
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Fundamental & Derived Quantities
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In mechanics, three fundamental quantities are used
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Length
Mass
Time
Will also use derived quantities
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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/m3
m

V
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Dimensional Analysis
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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
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Both sides of equation must have the same dimensions
Dimensions are denoted with square brackets
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Add, subtract, multiply, divide
Length – [L]
Mass – [M]
Time – [T]
Cannot give numerical factors: this is its limitation
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Dimensional Analysis, example
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Given the equation: x = 1/2 a t2
Check dimensions on each side:
[ L]
[ L]  2  [T 2 ]  [ L]
[T ]
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The T2’s cancel, leaving L for the dimensions of
each side
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The equation is dimensionally correct
There are no dimensions for the constant
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Conversion of Units
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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
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The ratio is called a conversion factor
Example 10 m/s  ? km/h
 1km  3600s 
10 m/s 

  36 km/h
 1000m  1h 
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Order of Magnitude
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Approximation based on a number of assumptions
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May need to modify assumptions if more precise results are
needed
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Order of magnitude is the power of 10 that applies
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In order of magnitude calculations, the results are
reliable to within about a factor of 10
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Uncertainty in Measurements
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There is uncertainty in every measurement, this
uncertainty carries over through the calculations
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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
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A significant figure is one that is reliably known
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Zeros may or may not be significant
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Those used to position the decimal point are not significant
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To remove ambiguity, use scientific notation
In a measurement, the significant figures include the first
estimated digit
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0.0075 m has 2 significant figures
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10.0 m has 3 significant figures
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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
The decimal point gives information about the reliability of the measurement
1500 m is ambiguous
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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
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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.
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Example: 25.57 m x 2.45 m = 62.6 m2
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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.
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Example: 135 cm + 3.25 cm = 138 cm
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The 135 cm limits your answer to the units decimal value
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Rounding
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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
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Used to describe the position of a point in
space
Coordinate system consists of
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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
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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
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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
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Based on forming a right
triangle from r and 
x = r cos 
y = r sin 
Cartesian to Polar
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r is the hypotenuse and  an
angle
y
tan  
x
r  x2  y2
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