Transcript WHAT IS PHYSICS?

WHAT IS PHYSICS?
Physics is simply the study of the physical world.
Everything around you can be described using the tools
of physics. The goal of physics is to use a small number
of basic concepts, equations, and assumptions to
describe the physical world.
Once the physical world has been described this way,
the Physics principles involved can be used to make
predictions about a broad range of phenomena.
For example, the same
Physics principles that are
used to describe the
interaction between two
planets can also be used to
describe the motion of a
satellite orbiting the Earth.
Many of the inventions, appliances,
tools, and buildings we live with today
are made possible by the application of
physics principles. Every time you take
a step, catch a ball, open a door,
whisper, or check your image in a
mirror, you are unconsciously using
your knowledge of Physics.
Physics is the most basic of the experimental sciences.
and provides the foundation for other scientific and
technical disciplines.
There are five major areas in Physics:
1. Newtonian Mechanics
Kinematics: How objects move.
Dynamics: The causes of motion: Newton's Laws.
Circular motion and Gravitation
Conservations Laws: Energy and Momentum
Oscillations
2. Fluid Mechanics and Thermodynamics
Fluid Mechanics: Fluids at rest and fluids in
motion.
Thermodynamics: The relationship between heat
and other properties.
3. Electricity and Magnetism
Electrostatics: Electric charge, field and potential.
DC Circuits: Electric current and direct-current
circuits.
Electromagnetism: Magnetic force and
electromagnetic induction
4. Waves and Optics
Wave motion.
Geometric Optics: reflection, refraction and
optical devices (mirrors and lenses).
Physical Optics: interference and diffraction.
5. Atomic and Nuclear Physics
Atomic levels, photoelectric effect, radioactivity,
fission and fusion.
UNITS, STANDARDS AND THE SI SYSTEM
The base units that will be used in this course
are: meter, kilogram, second
The SI length standard: the meter
meter (m): One meter is equal to the path
length traveled by light in vacuum during a
time interval of 1/299,792,458 of a second.
The SI mass standard: the
kilogram
kilogram (kg): One kilogram is
the mass of a Platinum-Iridium
cylinder kept at the International
Bureau of Weights and Measures
in Paris.
The SI time standard: the second
second (s): One second is the time occupied
by 9,192,631,770 vibrations of the light (of a
specified wavelength) emitted by a Cesium133 atom.
SYSTEME
INTERNATIONAL
The scientific
community follows
the SI Systeme
International,
based on the
metric system:
All physical quantities are expressed in terms of base
units. For example, velocity is usually given in units of
m/s.
All other units are derived units and may be expressed
as a combination of base units. For example: A Newton
is a unit of force: 1 N = 1 kg.m/s2
SI PREFIXES
MATHEMATICAL NOTATION
Many mathematical symbols will be used
throughout this course:
=
denotes equality of two quantities

denotes a proportionality
<
means is less than and
>
means greater than

two quantities are approximately
equal to each other
x
(read as “delta x”) indicates the change
in the quantity x

represents a sum of several quantities, also
called summation (sum of…)
PART I. SOLVING EQUATIONS
BASIC ALGEBRA:
adding
subtracting
multiplying
dividing
squared
square root
v  v  2a( s  so )
2
2
o
v  v  2a( s  so )
2
2
o
v v
a
2( s  so )
2
2
o
PART II. SCIENTIFIC NOTATION
The following are ordinary Physics problems.
Place the answer in scientific notation when appropriate
and simplify the units.
4.5  10-2 kg
-2 s
Ts  2

2.98x10
2.0  103 kg s 2
PART III. FACTOR-LABEL METHOD FOR
CONVERTING UNITS
Change 25 km/h to m/s
 25 km  1000 m  1 h 




 h  1 km  3600 s 
= 6.94 m/s
What is the conversion factor to convert km/h to m/s?
DIVIDE BY 3.6
What is the conversion factor to convert m/s to km/h?
MULTIPLY BY 3.6
PART IV. TRIGONOMETRY AND BASIC GEOMETRY
SOH CAH TOA
opp
b
sin  

hyp
c
c  a b
2
2
2
adj
a
cos  

hyp
c
opp b
tan  

adj
a
1.
c = 32 m
b
b
sin 55 
c

55º
a
b  csin 55  32(sin 55 ) = 26.2 m

c  a b
2
2
2
a  c b
2
2
 322  26.22 = 18.4 m
a = 18.4 m
b = 26.2 m
GRAPHING TECHNIQUES
Frequently an investigation will
involve finding out how
changing one quantity affects
the value of another.
The quantity that is deliberately manipulated is
called the independent variable.
The quantity that changes as a result of the
independent variable is called the dependent
variable.
1. Identify the independent and dependent
variables:
Time = independent
Position = dependent
2. Choose your scale carefully:
5 cm = 1 unit
3. Plot the independent variable on the horizontal (x)
axis and the dependent variable on the vertical (y)
axis.
4. If the data points appear to
lie roughly in a straight line,
draw the best straight line you
can with a ruler and a sharp
pencil.
5. Title your graph.
6. Label each axis with the name of
the variable and the unit.
INTERPRETING GRAPHS
There are three relationships that occur frequently in
Physics.
Graph A:
If the dependent variable varies directly with the
independent variable, the graph will be a straight line.
Graph B:
If y varies inversely with x, the
graph will be a hyperbola.
Graph C:
If y varies directly with the
square of x, the graph will be
a parabola.
Reading from the graph between data points is called
interpolation.
Reading from the graph beyond the limits of your
experimentally determined data points is called
extrapolation.
1. Suppose you recorded the following data during a study of the
relationship of force and acceleration. Prepare a graph showing
these data.
a. Describe the relationship between force and
acceleration as shown by the graph.
Force is directly proportional to acceleration
b. What is the slope of the graph?
2
y
40  10 30 kg×m/s
slope 


= 1.57 kg
2
25  6
x
19 m/s
c. What physical quantity does the slope represent?
The slope represents the mass.
d. Write an equation for the line.
y = kx + b
F =ma + 0
e. What is the value of the force for an acceleration of
15 m/s2?
F = ma + 0
= (1.57 kg) (15 m/s2)
= 24 N
f. What is the acceleration when the force is 50.0 N?
F =ma + 0
F 50 kg  m/s 2
a 
 31.8 m/s 2
m
1.57 kg
EXPERIMENTAL ERROR
When scientists measure a physical quantity, they do
not expect the value they obtain to be exactly equal to
the true value. Measurements can never be made with
complete precision. Therefore, there is always some
uncertainty in physical quantities determined by
experimental observations. This uncertainty is known
as experimental error.
There are two kinds of errors: systematic error and
random error.
A systematic error is
constant throughout a set
of measurements. The
results will be either
always larger or always
smaller than the exact
reading.
A random error is not constant.
Unlike a systematic error, a
random error can usually be
detected by repeating the
measurements.
Classify the following examples as
systematic or random error.
1. A meterstick that is worn at one end is used to
measure the height of a cylinder.
2. A clock used to time an experiment runs slow.
3. Two observers are timing a runner on a track.
Observer A is momentarily distracted and starts the
stopwatch 0.5 s after observer B.
4. Friction causes the pointer on a balance to stick.
5. An observer reads the scale divisions on a beaker as
one-tenths instead of one-hundredths.