Transcript Potential Energy

The Tarantula Nebula is
more than 1,000 light-years
in diameter -- a giant star
forming region within our
neighboring galaxy the
Large Magellanic Cloud
(LMC). Within the
Tarantula, intense
radiation, stellar winds and
supernova shocks from the
central young cluster of
massive stars, energize the
nebular glow and shape the
spidery filaments. Around
the Tarantula are other
violent star-forming regions
with young star clusters,
filaments and bubbleshaped clouds.
Homework #2 will be posted shortly
It will be due Wednesday, September 23, noon
A hallmark of science
is that
theories are testable
With Galileo’s observations, the revolution
begun by Copernicus was nearly complete…
 The structure of the universe had been totally
changed.
 The motions of the planets were understood, at least
from a geometrical perspective.
 Earth was no longer a “special” place in the universe.
 The crowning achievement was yet to come discovering the laws of nature and that naturally led to
the newly determined structure.
Sir Isaac Newton (1642-1727)
Invented calculus
Invented the reflecting
telescope
Connected gravity and
planetary forces
Universal Law of Gravitation
Between every two objects there is an attractive force,
the magnitude of which is directly proportional to the
mass of each object and inversely proportional to the
square of the distance between the centers of the
objects.
Orbital Paths from Law of Gravitation
●
●
●
Extending Kepler’s Law #1, Newton
found that ellipses were not the only
orbital paths.
All orbits are “conic sections”
– ellipse (bound)
– parabola (unbound)
– hyperbola (unbound)
Orbital motion takes place around
the center of mass
The Center of Mass
In Kepler's Laws, the Sun is fixed at a point in space (a
focus of an ellipse) and the planet revolves around it.
Why is the Sun privileged?
Kepler had mystical ideas about the Sun, endowing it
with almost god-like qualities that justified its special
place.
Newton demonstrated that the the Sun does not occupy
a privileged postion and in the process he modified
Kepler's 3rd Law.
The center of mass is familiar to anyone who has ever played
on a see-saw. The fulcrum point at which the see-saw will
exactly balance two people sitting on either end is the center
of mass for the two persons.
m1d1 = m2d2
Newton realized that in the planet-Sun system the
planet does not orbit around a stationary Sun (a planet
exerts as much gravitational force on the Sun as the
Sun does on a planet). F = Gm m /d2
g
1
2
 Instead, Newton proposed that both the planet and
the Sun orbited around the common center of mass for
the planet-Sun system.
 This led Newton to modify Kepler's 3rd Law.
Recall Kepler’s 3rd law: P2 / a3 = constant
Newton’s Version of Kepler’s Third Law
2
2
3
P = 4 a / G (m1 + m2)
G is known as the universal gravitational constant.
If you can measure the orbital period of two objects (P)
and the distance between them (a), then you can calculate
the sum of the masses of both objects (m1 + m2).
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
The very first ever Blonde GUY joke..... And well worth the wait!
An Irishman, a Mexican and a Blonde Guy were doing
construction work on scaffolding on the 20th floor of a building.
They were eating lunch and the Irishman said, "Corned beef and
cabbage! If I get corned beef and cabbage one more time for
lunch, I'm going to jump off this building."
The Mexican opened his lunch box and exclaimed, "Burritos
again! If I get Burritos one more time I'm going to jump off, too."
The blond opened his lunch and said, " Bologna again! If I get a
bologna sandwich one more time, I'm jumping too."
The next day, the Irishman opened his lunch box, saw corned
beef and cabbage, and jumped to his death.
The Mexican opened his lunch, saw a Burrito, and jumped, too.
The blonde guy opened his lunch, saw the bologna and jumped
to his death as well.
At the funerals, the Irishman's wife was weeping. She said, "If I'd
known how really tired he was of corned beef and cabbage, I
never would have given it to him again!"
The Mexican's wife also wept and said, "I could have given him
tacos or enchiladas ! I didn't realize he hated Burritos so much."
Everyone turned and stared at the blonde's wife. The blonde's
wife said …
"Don't look at me. He makes his own lunch"
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.