Why should we care about sedimentary rocks?
They contain oil and natural gas
They contain fossils
They tell us about past environments and the history of an area
Where does hydrocarbon energy come from?
Ultimately from the sun
plants store energy till used by us
What happens when we use the energy in our cars -- is it used up?
Fuel turns engine
engine moves vehicle
engine heats up--> cools and releases energy
Law of conservation of energy
Energy is never created or destroyed just converted from one form to another
What are some forms of energy?
What is energy?
The ability to do work
What is work?
Force acting on something and moving that object due to the force and in the
direction of the force.
Is work done on the following:
a book pushed across a desk
a rock is pushed on but doesn’t move
Work = Fdà (Kgm/s2)(m) = Kgm2/s2
This is also know as a Joule
Energy is the ability to do work
Energy uses the same units as work.
Potential energy:
The potential to do work--stored energy
energy at rest
rock on top of a hill
an arrow pulled back in a bow
a car sitting still
Gravitational potential energy
potential energy due to an elevated position
PE = mgh
m is mass in Kg
g is gravitational acceleration (9.8 m/s2)
h is the height above the surface in meters
ex// a rock weighs 1500 kg and is elevated 10 meters above the ground. What is its gravitational potential energy?
PE = (1500 Kg) (9.8 m/s2) (10 m) =
147,000 Kgm2/s2
Kinetic energy
Energy of motion
Examples of kinetic energy?
KE =1/2 mv2
m is mass in Kg
v is velocity (m/s)
(Kg) (m/s)2 à =Kgm2/s2
ex// what is the kinetic energy of a 4 Kg bowling ball traveling down a lane at 10 m/s?
KE = 1/2 (4 Kg) (10m/s)2 = 200 Kg m2/s2
As something slides along a smooth surface, what type of energy does it have?
Energy of a system is defined as all the energy together
In a conservative system, the energy in the system before motion is the same as the energy after
motion
In a non-conservative system the energy is transformed and not stored for later use
Conservative forces are found in conservative energy systems
When a conservative force acts, the work it does is stored in the form of energy that can be
used later
Gravity is a conservative force
Calculate the work done if you were to lift a 3kg box 2 meters.
What is the work that gravity does on this box if you let go of it when it is 2 meters high?
The energy in the system was stored as potential energy when the box was lifted.
What is the total NET work you just calculated that was done to the box?
In a conservative system, the net work done by a force on a closed path is zero!
Non conservative forces are when the work done does not store the energy for later use. Energy
is transformed immediately
A box being pushed across a floor is a non-conservative system.
Work is done to slide a box across the floor. When you stop applying force to the box,
will move?
The transfer of energy via friction is released as heat and not available to use to move the
box later.
Energy and Society
What is meant when we are told to conserve energy?
How is this different from the physics idea of the conservation of energy?
How does Oil, wind, solar etc relate physics to energy in today’s society?
Why are the major sources of energy in the USA from Coal, oil and natural gas?
These are known as hydrocarbons…what does this mean?
Hydrocarbons are VERY efficient sources of energy
This means that the energy required to break the hydrocarbon bond is less than the energy
produced in the reaction
This is not true for most reactions in chemistry
Why are hydrocarbons good for creating energy?
Hydrocarbons react with oxygen
CH4 + 2O2 à CO2 + 2H2O + energy (methane)
C3H8 + 5O2 à 3CO2 + 4H2O + energy (propane)
C8H18 + 25O2 à 16CO2 +18H2O + energy (gasoline)
What are the products for ALL these reactions?
What are some side affects using hydrocarbons?
Why should we be concerned about CO2?
Natural component of the atmosphere--> balance
excess CO2 destroys balance --> reflect heat back to earth
Global warming--> yea or nay