Transcript envsci_15_patton_lec..

• Energy Update!
• Homework Assignment Help
• Review Last Lecture
• Energy and Society
• Today’s Material:
• Energy
• Heat
• Heat Activity (Probably Next Monday)
• Homework 2: Wed 9/10/14
• Chapter 3 Exercises 1, 2, 5, 6, 9, 10
Renewable energy capacity grows at fastest ever pace
Green technologies now produce 22% of world's electricity
Wind turbines in China.
More than $250bn (£150bn) was
invested in "green" generating
systems in 2013, although the
speed of growth is expected to
slacken, partly because politicians
are becoming nervous about the
cost of subsidies.
The current growth rate for
installing new windfarms and
solar arrays is impressive but
the IEA believes it is not
enough to meet climate
change targets, triggering
calls in Brussels from green
power lobby groups for
Europe to adopt tougher,
binding targets.
http://www.theguardian.com/environment/2014/aug/28/renewable-energy-capacity-growsfastest-ever-pace?CMP=twt_gu
We Are On The Verge Of An Electric Car Battery
Breakthrough
Electric vehicles are cool. They’re inexpensive to operate, can make
our air cleaner, and help reduce the amount of climate changecausing gases released into the atmosphere. But right now, they’re
also mostly just for rich people. The initial cost of buying the car,
combined with their limited availability, is just too much for most
people to justify making the switch.
That could soon change, though, because investment pundits think
that Tesla Motors is on the verge of achieving something big: A
battery cheap enough to make electric vehicles cost-competitive with
conventional cars. Daniel Sparks at Motley Fool is reporting that the
company is on the right track towards developing a battery that costs
only $100 per kilowatt-hour — a cost widely believed to be the
threshold where electric vehicles can finally be cost-competitive.
HOMEWORK ASSISTANCE
CH 1: 1
CH 2: 1, 3, 4, 5
The sun’s electromagnetic spectrum and some of the
descriptive names of each region. The numbers
underneath the curve approximate the percent of energy
the sun radiates in various regions.
0.4 μm = 400 nm
0.7 μm = 700 nm
The hotter sun not only radiates more energy than that of the cooler earth (the area
under the curve), but it also radiates the majority of its energy at much shorter
wavelengths. (The area under the curves is equal to the total energy emitted, and the
scales for the two curves differ by a factor of 100,000.)
Potential and kinetic energy. (a) Gravitational potential energy of the
skier becomes kinetic energy as she heads down the slope. (b) Elastic
potential energy stored in the bow becomes kinetic energy of the arrow.
Sunlight that strikes a surface at an angle is spread over a
larger area than sunlight that strikes the surface directly.
Oblique sun rays deliver less energy (are less intense) to a
surface than direct sun rays.
End-use energy consumption, by sector, for three countries in
the early twenty-first century.
Why do these countries have a different breakdown of energy uses?
Japan is a compact industrialized
country, with a well developed rail
system, so uses a greater fraction
of its energy for industry than does
the USA.
Ghana is a typical developing
country and has much smaller
industrial and commercial sectors,
so devotes most of its limited
energy to residential uses.
Energy consumption by sector for the United States, (a) with
end-use accounting and (b) accounting for primary energy.
End-use energy is measured by the amounts of energy that
actually reach the end user. Primary energy is the fuel energy
that goes into the production of energy (i.e. the energy that
originally goes into the power plant).
Why are these percentages different?
TODAY’S MATERIAL
http://image.tutorvista.com/content/feed/tvcs/push20and20pull.JPG
Force can be thought
of as a push or pull
upon an object.
When forces are
balanced, there is
no acceleration.
http://www.bbc.co.uk/bitesize/standard/physics/images/tug_of_war.gif
When forces are
unbalanced, there
is acceleration.
http://www.bbc.co.uk/bitesize/standard/physics/images/trolley.gif
Force = Mass X Acceleration
The 3 fundamental forces: (a) Gravity governs the large-scale structure
of the universe. It holds you to Earth and keeps a satellite in orbit.
Gravitational potential energy is the energy source for hydroelectric
power plants. (b) The electromagnetic force is responsible for the
structure of matter at the molecular level; the associated potential
energy is released in chemical reactions such as those that occur in
burning fuels. Electromagnetism is also involved in the production and
transmission of electrical energy. (c) The nuclear force binds protons
and neutrons to make atomic nuclei. The associated potential energy is
the energy source for nuclear power plants.
Chemical reactions in a battery separate positive and negative charge.
Connecting an external circuit, such as the lamp shown here, allows the
battery to deliver electrical energy as charge flows through the circuit.
(a) A simple electric generator consists of a single wire loop rotating
between the poles of a magnet. The stationary brushes allow current to
flow from the rotating contacts to the external circuit. A practical
generator has many loops, each with many turns of wire. (b) This large
generator produces 650 MW of electric power.
ƛ = c/F
The electromagnetic spectrum. Electromagnetic waves are
Wavelength
= waveinspeed/frequency
characterized
by their frequency
hertz (wave cycles per second) or
their wavelength in meters (the distance between wave crests). The two
are inversely
Note
E =related.
hf = hc/
ƛ the highly nonlinear scale, with each tick
mark representing a factor of 1,000 increase or decrease in frequency or
wavelength. The Sun’s energy output is mostly in the visible and
adjacent infrared portion of the spectrum, with a little ultraviolet.
Quantifying Energy
1 Joule = 1 Watt Second
Lift a 2 pund book 4 inches, you will have expended about 1
Joule of energy
1 Calorie = the amount of energy it takes to raise the
temperature or 1 gram of water by 1 degree Celsius
1 British Thermal Unit (BTU) = the amount of energy required
to raise the temperature of 1 pound of water by 1 degree
Fahrenheit
Table 3.1 shows some energy and power units.
Work = Force X Distance
Force and work. (a) When you lift a bowling ball, you apply a force in the
direction of its motion. You do work on the ball, in this case increasing
its gravitational potential energy. (b) When you carry the ball
horizontally, you apply a force to counter its weight, but you don’t do
work on the ball because the force is at right angles to its motion. (c)
When you apply an upward force to stop a falling ball, the force is
opposite the ball’s motion, so here you do negative work that reduces
the ball’s kinetic energy.
Work = mass X gravity X height
Rising out of a knee bend requires that I apply a 600-N force over a
distance of 0.17 m, resulting in 100 J of work done. Repeating once per
second gives a power output of 100 W.
Class Review:
Energy Update!
Energy
Work
Next Class
Heat
Heatflow
Kinetic energy increases with the square of the speed. Shown here is
kinetic energy versus speed for a Honda Civic compact car (empty
weight 1,268 kg) and a Ford Excursion SUV (empty weight 3,129 kg),
each with a 68-kg driver. The weight difference accounts for much of the
difference in fuel efficiency between these vehicles.
Temperature measures the average molecular kinetic energy. At lower
temperatures, the molecules of a gas have lower kinetic energy and
move more slowly; at higher temperatures, the molecules have higher
kinetic energy and move more quickly.
Four temperature scales compared: Kelvin, Celsius, Rankine, and
Fahrenheit.
Conductive heat flow H through a slab of material with conductivity k is
given by Equation 4.1. Th and Tc are the temperatures on the warmer
side and the cooler side of the slab, respectively. A is the slab area, and
d is its thickness.
Class Review:
Energy Update!
Energy
Society
Next Class
Forms of Energy
Making Energy
Quantifying Energy
Work
Friction
Estimations
Factors that result from climate change and that can then amplify the causes of climate
change are known as “positive feedbacks.” Some of the key positive feedbacks include
thawing of permafrost (resulting in the release of previously trapped methane), forest
loss due to drought (resulting in the release of carbon sequestrated in the wood) and the
melting of the polar ice-caps (resulting in a reduced capacity to reflect solar energy from
the earth’s surface)
http://www.climate-leaders.org/climate-change-resources/climatechange/causes-of-climate-change