energy -- the ability to do work

Energy is measured in joules

Forms of Energy

1.     Mechanical  -- matter that is in motion

2.     Heat -- the internal motion of all the atoms of a piece of matter
                -- it is also formed due to friction
                --  it causes changes in temperature ( average energy) and phase changes

3.     Chemical -- the energy required to bond atoms together into molecules
                        -- when bonds are formed energy is needed and when bonds are broken energy is released

fossil fuels -- contain stored solar energy in their chemical bonds

**  Fossil fuels are considered to be nonrenewable energy resources.

Fossil fuels are a major source of energy in the United States.

4.    Electromagnetic - moving electric charges (electricity) and the energies in the
                                     electromagnetic spectrum (light, Xrays, radio)

solar energy -- energy from the Sun contains electromagnetic energy

-- Solar energy is the major source of energy for the Earth.

-- Wind energy and moving water and forms of energy which are driven by energy inputs from the Sun.

biomass energy -- that energy obtained from living materials or their products (like methane gas)

**  Biomass energy can ultimately be traced back to the Sun.

5.   Nuclear -- the energy that holds atoms together
                    -- nuclear fission releases this energy when atoms are split
                    -- nuclear fusion releases this energy when atoms are fused or pushed together

6.  Geothermal energy -- that energy found deep within the Earth's surface (in geysers, volcanoes, hot springs, etc.)

**  Solar energy, wind, moving water, and biomass are examples of renewable energy resources.

States of Energy

a.)  Potential Energy (PE) -- is energy that is stored due to its position or shape of an object
                                              exs.  a stretched rubber band or a rock on top of a mountain

Gravitational Potential Energy (GPE) -- energy that is dependent on an object's height from
                                                             the surface of the Earth

Formulas:
 
GPE = Weight x Height  OR GPE = wh

-- weight is measured in Newtons of force and height in meters

 

OR GPE = mgh

GPE = gravitational potential energy (J) m = mass (kg) g = acceleration of gravity (m/s2) h = height (m)

Problems:

1.  A rock with a mass of 10 kg falls 7 m.  What amount of potential energy did the rock have before
     it fell the 7 meters?

GPE = mgh

m = 10 kg
g = 9.8 m
            s2
h = 7 m.

GPE = 10 kg (9.8 m) 7 m = 686 kg m2 = 686 J.
                            s2                        s2
 

2.  An army packet of supplies having a mass of 300 kg., was dropped from a height of 500 meters, what
     amount of potential energy does the packet have?

GPE = mgh

m = 300 kg
g =  9.8  m
              s2
h =  500 m

GPE = 300 kg (9.8 m)  500 m  = 1,470,000 J
                               s2

b.)  Kinetic Energy -- objects in motion have kinetic energy
                                -- the kinetic energy of an object depends on its mass and its velocity
 

Formula:

KE = (mass x velocity 2)    OR  KE = 1/2 mv2
                    2

Problems:

1.   In an automobile collision, which has a greater influence on the energy impact in the accident, mass or velocity?

Answer:  Doubling the velocity would have a greater influence than doubling the mass of the auto, as the velocity
               term is squared, so a car traveling at 2 times the speed would have 4 times the kinetic energy.
 

2.    Determine the kinetic energy of a 80 kg man jogging at 4 m
                                                                                             s
 

KE = 1/2 mv2   m = 80 kg   v = 4 m
                                                     s

KE = 1/2 80 kg (4 m) 2 =  640 J
                              s
 

Energy Conversions

     - changes in the form of energy from one to another are called energy conversions

-Kinetic to potential conversions

     - a pendulum swinging is a good example
     - to get a pendulum going the weight must be raised (kinetic) to a new height (potential)
     - when it is released that potential is converted into kinetic along the way until such time as it has returned to its
       original height , at which time its energy is now all kinetic (movement , no height)
     - as it swings to the other side, it slows down ( losing kinetic) but gains height (potential) to the point where it
       stops at its highest point (potential, no kinetic)
     - the cycle repeats itself over and over
 
 
 

**  The image at the right shows the conversion of potential to kinetic energy and vice versa in a bouncing ball.

**  The image at the right shows the energy interconversions involved in a pendulum (as discussed above)

Note:  In all energy conversions some of the energy is going into forms that we don't see and/or want
          - there is friction between the rope and the air, and the top of the pendulum. so some of the energy is "lost"
         - this is why at every swing it goes less high each time and eventually stops

Energy Transformations

**  Energy may be transformed in many ways.    This occurs repeatedly in our everyday activities.

ex.   The chemical energy in gasoline is transformed into mechanical energy in an automobile engine.

-- Almost all energy transformations involve some energy being degraded to the less useful form "heat".

Other Energy Conversions

battery --- changes chemical energy to electromagnetic energy

waterfall -- mechanical energy is converted to electromagnetic energy

engine -- chemical energy is converted to heat and mechanical energy
 
 

**  The table at the right shows a variety of possible energy conversions.

 

Conservation of Energy

     - states that energy cannot be created or destroyed BUT may be converted
       from one form to another
 

Albert Einstein (1905)  Theory of Relativity

-- explained how mass and energy can be converted into each other
-- theory of relativity which says that a small amount of mass (M) can
    produce a large amount of energy ( C2) if they are converted from one to the other
-- this theory is important in understanding what goes on in the non ordinary reactions of nuclear reactors and the
    stars
 

gravity -- a force which pulls an object toward every other object

Factors determining Gravitational Force

1.   The greater the masses of the objects involved, the greater the pull of gravity.

2.   The closer two objects are together, the greater the pull of gravity between them.

Gravity is a force acting on orbiting objects and projectiles.