Download Chemical potential energy

Chapter 4
Energy
http://www.nsf.gov/news/special_reports/olympics/snowboarding.jsp
Sec 1. The Nature of Energy
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Energy—the ability to cause change.
Energy has several different forms such as
Electrical—making toast or turning on a light
 Chemical—energy stored in food or gasoline
 Thermal—from the sun, warming the planet
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It can be transferred from one form to
another.
Kinetic Energy
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Kinetic Energy—energy in the form of motion.
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The amount of kinetic energy (KE) depends on 2
quantities:
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Examples—a spinning bicycle wheel, kicking a ball.
The mass of the moving object and its velocity.
The more mass, the more kinetic energy.
Example: a truck and a motorcycle are both
moving at 100 km/hr. Which one has more KE?
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Answer: the truck, because it has more mass.
Calculating Kinetic Energy
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You can calculate kinetic energy using
this equation.
Kinetic Energy = ½ mass x velocity squared
 KE = ½ m x v2
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The SI unit of energy is the joule (J)
Potential Energy
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Energy does not always involve motion.
Potential Energy—stored energy due to position.
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The amount of potential energy (PE) depends on the
objects position.
There are different types of potential energy.
Elastic potential energy—energy stored by
something that can compress or stretch (ex. rubber band)
Chemical potential energy—energy stored in
chemical bonds (ex. gasoline is stored until you start your car)
Gravitational Potential
Energy
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Gravitational Potential Energy (GPE)—the
energy stored by objects that are above Earth’s
surface.
The amount of GPE depends on 3 things
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Mass, acceleration due to gravity, & height above
the ground.
The amount of GPE can be calculated
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GPE = mass x 9.8m/s2 x height
GPE = m x 9.8 m/s2 x h
or GPE = mgh
Changing GPE
Sec 2. Conservation of Energy
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Changing forms of energy
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When you turn on a light bulb it
converts electrical energy into light
energy and thermal energy.
Fuel stores energy in chemical
bonds. A car engine transforms
chemical PE into KE.
Mechanical Energy—the total
amount of potential and kinetic
energy in a system.
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Mechanical energy = PE + KE
Falling Objects
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As an object falls, its potential
energy decreases and its kinetic
energy increases.
The amount of mechanical energy of
a falling object always remains the
same.
Energy transformation also occurs
when a baseball is hit.
Close to the ground it has mostly
KE. At its highest point it has
mostly PE, but the amount of
mechanical energy is constant.
Swinging
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On a swing or a pendulum the mechanical
energy is also constant.
To get moving, you need KE. As you rise
higher, your GPE increases. As you move
down, your KE increases. Mechanical Energy
is constant.
Law of Conservation of Energy
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Law of Conservation of energy—
states that energy cannot be created
or destroyed.
Sometimes it is hard to see energy
conserved.
Ex. Friction can cause some
mechanical energy to change into
thermal energy (heat).
Ex. The sun can convert a small
amount of mass into a large amount
of energy using nuclear fusion.
Law of Conservation of Energy
Continued
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Your body follows the law
of conservation of energy.
Ex. Chemical potential
energy is stored in the food
you eat.
 Ex. Your body stores energy
in fat and other chemicals.
 Ex. Your body converts the
energy to make you move.
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