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Energy
Chapter 15
Energy is the ability to do work
* Work is done when a force moves an object through a distance.
* Work = Force X Distance
* Work is a transfer of energy
* Work and energy are measured in Joules (J)
* 1 Joule = 1 Newton*meter
There are two basic types of energy: Kinetic and Potential
* Kinetic energy – energy of motion
* Amount of kinetic energy depends on an object’s mass and
speed
KE = ½ mv2
* Potential energy – energy that is stored as a result of position or
shape.
* Stored energy can eventually be converted to kinetic energy
* Gravitational potential energy is potential energy that
depends upon an object’s height
* An object’s gravitational potential energy depends on
its mass, its height, and the acceleration due to
gravity.
PEg = mgh = Fgh
(Fg = mg)
* Elastic Potential Energy – the energy that an object has
that is stretched or compressed.
* Ex. Rubber band, spring
There are several forms of energy. Each of these forms can be
converted to other forms.
* Mechanical energy is the energy associated with the motion and
position of everyday objects.
* Mechanical energy is the sum of an object’s potential energy
and kinetic energy.
* Ex. Speeding trains, bouncing balls
* Thermal energy is the total potential and kinetic energy of all
the microscopic particles in an object.
* When an object’s atoms move faster, its thermal energy
increases and it becomes hotter.
* Chemical energy is the energy stored in chemical bond.
* When bonds are broken, the released energy can do work.
* Ex. Coal, gasoline
* Electrical energy is energy associated with electrical charges.
* Batteries convert chemical energy to electrical energy.
* Ex. Lightning
* Electromagnetic energy is a form of energy that travels through
space in the form of waves.
* Ex. Visible light, X-rays
* Nuclear energy is energy stored in atomic nuclei.
* Nuclear power plants use nuclear fission and nuclear fusion
15.2 Energy Conversions and Conservation
Energy conversion is the process of changing energy from one form to
another.
The Law of conservation of energy states that energy cannot be
created or destroyed.
* Energy is often converted into other forms.
* Friction is often the cause of energy changes (reduces
efficiency)
* Gravitational potential energy of an object is converted to the
kinetic energy of motion as the object falls.
Ex. Wind-up toys: elastic potential energy  kinetic energy
Ex. Light bulbs: electrical energy  thermal/electromagnetic
Ex. Riding a bike: kinetic energy  thermal energy (heat of tires)
Ex. Avalanche: gravitational potential energy  kinetic energy
Ex. Food: Chemical potential energy  kinetic energy
Ex. Pendulum: Potential energy  Kinetic energy
Ex. Pole vaulter: Kinetic elastic potential →kinetic energy 
gravitational potentialkinetic
Conservation of Mechanical Energy:
KE + PE = KE + PE
Einstein’s equation, E = mc2, says that energy and mass can be converted
into each other.
* Energy is released as matter is destroyed, and matter can be
created from energy