Transcript Energy and Energy Resources

Work & Energy
7.1 – What Is Energy?
pp. 164-172
TERMS TO LEARN
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Energy – the ability to do work
Kinetic energy – the energy of
motion
Potential energy – the energy of
position or shape
Mechanical energy – the total
energy of motion AND position of
an object
ENERGY
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Energy is the
ability to do work;
work is the
transfer of
energy.
Both energy and
work are
expressed in
Joules (J).
ENERGY
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When a given amount of work is done,
the same amount of energy is involved.
ENERGY
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The tennis player is
doing work on her
racket because she
has energy
When she does work
on the racket, the
racket gains the
ability to do work on
the ball.
ENERGY
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Energy is transferred from the
tennis player to the racket.
When the racket does work on the
ball, the ball gains the ability to do
work on something else. Energy is
transferred from the racket to the
ball.
TYPES OF ENERGY

Kinetic Energy (K.E.)
 Depends on:
 Speed and
 Mass
 Speed has more of an effect on
Kinetic Energy than mass because
speed is squared in the equation.
KINETIC ENERGY
Equation for K.E.:
K.E. = ½ m×v 2
 Where K.E. is kinetic energy
measured in joules (J)
 m is mass measured in kg
 v is speed measured in m/s
KINETIC ENERGY
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The faster something is moving, the more kinetic
energy it has.
Thermal energy, sound energy, electrical energy
and light energy can all be forms of kinetic energy.
POTENTIAL ENERGY
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Also known as P.E. or
G.P.E.
Energy of position or
shape
Gravitational potential
energy depends on:
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Weight and
Height (distance above
Earth’s surface)
POTENTIAL ENERGY
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The stored
potential energy
of the bow and
string allows
them to do work
on the arrow
when the string is
released
POTENTIAL ENERGY
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Equation for G.P.E.:
G.P.E. = weight × height
G.P.E = mass × g × height
Chemical energy, electrical energy,
sound energy and nuclear energy
can be forms of potential energy
Solving Problems
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A 2 kg rock is at the edge of a cliff 20
meters above a lake.
It becomes loose and falls toward the
water below.
Calculate its potential and kinetic
energy when it is at the top and when
it is halfway down.
Its speed is 14 m/s at the halfway
point.
Solving Problems
Looking for:
1.
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…initial EK, EP and EK, EP half way down.
Given:
2.
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mass = 2.0 kg; h = 20 m
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v = 14 m/s (half way)
Relationships:
3.
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EP =mgh
EK = ½ mv2
Assume rock starts from rest.
Solving Problems
4.
Solution
m = 20 kg
 Draw a free body diagram.
 EP = (2 kg)(9.8 N/kg)(20
m)
= 392 J at top
 EP = (2 kg)(9.8 N/kg)(10
m)
= 196 J half way
 EK = 0 J, rock is at rest
 EK = (1/2)(2 kg)(14
m/s)2
= 196 J half way
h = 20 m
h = 10 m
EP = mgh
EK = 0 J
EP = mgh
EK = ½ mv2
MECHANICAL ENERGY
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Total energy of motion and position
M.E. = K.E. + P.E.
Mechanical energy = kinetic energy +
potential energy
Mechanical energy can be all kinetic
energy, all potential energy, or some of
both.
MECHANICAL ENERGY
Mechanical energy remains constant, so
when the amount of potential energy
increases, the amount of kinetic energy
must decrease. When the amount of
kinetic energy increases, the amount of
potential energy must decrease.
ENERGY CONVERSIONS
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Energy cannot be created nor destroyed…it
can only be converted from one form to
another.
FORMS OF ENERGY
Thermal energy – the total energy of
the particles that make up an object.
1.
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The higher the temperature, the faster
particles move and the more K.E. they
have
Thermal energy also depends on the
number of particles there are in a
substance.
FORMS OF ENERGY
2.
3.
Chemical energy – the energy of a
compound that changes as its atoms
are rearranged to form new
compounds. Chemical energy is a
form of potential energy.
Electrical energy – the energy of
moving electrons. Electrical energy
can be either K.E. or G.P.E.
FORMS OF ENERGY
4.
5.
6.
Sound energy – caused by an object’s
vibrations. Sound energy can be a form of
either K.E. or P.E.
Light energy – produced by the vibrations
of electrically charged particles.
Nuclear energy – the energy associated
with changes in the nucleus of an atom.