Transcript Slide 1

Jupiter rules the sky in this labeled
view of a starry September night
from the Alborz mountains in Iran,
complete with the trail of a red
flashlight illuminating the mountain
road.
On September 21st (today) Jupiter
is at opposition, the point opposite
the Sun along its orbit, rising just as
the Sun sets. For this opposition,
Jupiter will be slightly brighter and
closer to planet Earth than in any
year since 1963.
Answers to Homework #1 are now posted
Homework #2
Questions 1 – 16 due by 5:00 pm, Wednesday.
Questions 17 – 20 due by 1:00 pm, Thursday.
Homework #3 will be posted shortly, due Tuesday.
Exam #1 Thursday, Sept. 30
Review session Tuesday, Sept. 28, time and place to
be announced
The Activities page of the class website now
has a number of out-of-class activities posted.
A Universe of Matter and Energy
What is matter?
What is energy?
Matter – material such as rocks,
water, air; “stuff” composed of
atoms
Energy – makes or has the
potential to make matter move!
The history of the universe, including biological
organisms, is based upon the interplay between
matter and energy.
Three Basic Types of Energy
• kinetic
– energy of motion
• potential
– stored energy; e.g., chemical,
gravitational, electrical, etc.
• radiative
– energy transported by light
(electromagetic radiation)
Conservation of
Energy
Fundamental law of
nature
Energy can be neither
created nor destroyed
It can change form or be
exchanged between objects.
K.E.
The total energy content of
the Universe was determined
in the Big Bang and remains
the same today.
P.E.
R.E.
Kinetic Energy (K.E.):
energy of motion
K.E. = 1/2 mv2
(m is mass, v is velocity)
On the microscopic level:
temperature
is a measure of the
AVERAGE kinetic energy
of particles within a substance
Temperature Scales
Temperature vs. Heat
●
●
lower T
higher T
same T
Temperature is the average
kinetic energy.
Heat (thermal energy) is the
total kinetic energy.
less heat
more heat
Sound waves are a form of kinetic energy on
a microscopic level
(organized vibration of molecules)
Applying what we’ve learned -
pizza vs. soup
caution in the kitchen
Potential Energy:
Energy that is “stored” within an
object and that has the potential of
being released in a different form
Gravitational Potential Energy
●
gravitational potential energy is
the energy which an object stores
due to its ability to fall
g
●
It depends on:
–
–
–
m
the object’s mass (m)
the strength of gravity (g)
the distance which it can fall (d)
●
P.E. = mgd
d
●
gravitational potential energy
●
P.E. = mgd
g
Mass-Energy Potential Energy
●
●
mass-energy: energy is stored in
matter itself
this mass-energy is what would
be released if an amount of mass,
m, were converted into energy
E = mc2
[ c = 3 x 108 m/s
is the speed of light]
Chemical Potential Energy
●
Chemical potential energy:
energy stored chemical bounds
There are many additional
examples of potential energy. e.g.,
stretched springs, …
Energy, while
conserved, can be
transformed from one
type of energy to
another
Potential
Kinetic
Potential
Kinetic
Kinetic
Potential
Orbits & Energy
Uphill
Maximum
Potential
Energy
Maximum
Kinetic
Energy
Downhill
From the
perspective of
energy, which
planet is more
difficult to reach
from the Earth?
Mars
Venus
From the
perspective of
energy, which
planet is more
difficult to reach
from the Earth?
Mars
It is “uphill”
ConceptTest
The gravitational potential energy of an interstellar
cloud of gas that is slowly shrinking in size …
(yellow) stays the same
(red) slowing changes into other forms of energy
(green) slowly increases
(blue) interstellar clouds do not have gravitational
potential energy
ConceptTest
The gravitational potential energy of an interstellar
cloud of gas that is slowly shrinking in size …
(yellow) stays the same
(red) slowing changes into other forms of energy
(green) slowly increases
(blue) interstellar clouds do not have gravitational
potential energy
ConceptTest
In the not too distant future scientists will develop an
engine that produces more energy than it uses. This
statement is …
(yellow) likely to be true
(red) false
(green) difficult to determine if this will happen or not.
(blue) this has already happened, but the government is
suppressing this discovery.
ConceptTest
In the not too distant future scientists will develop an
engine that produces more energy than it uses. This
statement is …
(yellow) likely to be true
(red) false
(green) difficult to determine if this will happen or not.
(blue) this has already happened, but the government is
suppressing this discovery.
Radiative energy:
energy carried by
electromagnetic
radiation (light).
Light
An “electromagnetic wave” through
which energy is transported.
Properties of Waves
WAVELENGTH (: Distance
between adjacent crests
FREQUENCY (f): number of crests that pass through a point
each second. It is measured in units of hertz (Hz), which are
the number of cycles per second.
AMPLITUDE: A measure of the strength of the wave.
SPEED (s): how fast the wave pattern moves.
For any wave:
s=f
Light as a Wave
• The speed of light is a constant: s = c !!!
• Therefore, for light:
f=c
• The higher f is, the smaller  is, and vice versa.
• In the visible part of the spectrum, our eyes recognize
f (or ) as color!
Light as a Particle
 Light can also be treated as photons – packets of energy.
 The energy carried by each photon depends on its frequency
(color)
 Energy:
E = hf = hc/  [“h” is called Planck’s Constant]
Shorter wavelength light carries more energy per photon.
The Electromagnetic Spectrum
lower
energy
higher
energy