Transcript zero height position

Chapter 9
Energy and Energy
Resources
Section 1
What is Energy?
Energy and WorkWorking together
What is energy?
Energy is the ability to do work
What is work?
Work occurs when a force causes an
object to move in the direction of the
force. (Work transfers energy)
Kinetic Energy is
Energy of Motion
• An object which has motionwhether it be vertical or horizontal
motion- has kinetic energy (KE)
• Three forms of KE are vibrational,
rotational, and translational
• To keep it simple, we will focus on
translational KE or the energy due
to motion from one location to
another
Potential Energy Is
Energy of Position
• Potential energy is the energy
an object has because of its
position or shape.
Potential Energy Is
Energy of Position
• When in their
resting position,
they have no
energy. The
potential energy
comes from the
change in shape
or position from
it’s usual shape
Potential Energy Is
Energy of Position
• A rubber band
is another good
example of
potential
energy.
No energy
potential
energy
• Gravitational potential energy is
the energy stored in an object as
the result of its vertical position or
height.
• The gravitational potential energy
of the massive ball of a demolition
machine is dependent on two
variables - the mass of the ball and
the height to which it is raised.
• There is a direct relation between
gravitational potential energy and
the mass of an object.
• More massive objects have greater
gravitational potential energy.
• There is also a direct relation
between gravitational potential
energy and the height of an object.
• The higher that an object is
elevated, the greater the
gravitational potential energy.
To determine the gravitational potential energy of
an object, a zero height position must first be
arbitrarily assigned. Typically, the ground is
considered to be a position of zero height. In the
lab, the desk could be zero height.
Since the gravitational potential energy of an object
is directly proportional to its height above the zero
position, a doubling of the height will result in a
doubling of the gravitational potential energy. A
tripling of the height will result in a tripling of the
gravitational potential energy.
Forms of Energy:
Thermal Energy
• All energy involves either motion or
position
• Thermal energy: all particles of matter
are in constant motion so they have
kinetic energy. Particles also have
energy because of molecular
arrangement
• Thermal energy is the total energy of
the particles that make up an object
Forms of Energy:
Chemical Energy
• Chemical energy is the energy of a
compound that changes as its atoms
are rearranged to form new
compounds
• Chemical energy is a form of
potential energy
• When compounds, like sugar in some
foods are formed, work is done to
bond the atoms to form molecules
Forms of Energy:
Electrical Energy
• Electrical Energy is the energy of
moving electrons
• When an electric appliance is
plugged in to an outlet, the electrons
in the wires move back and forth
transferring energy and producing
the work of the stereo which is to
produce sound.
• Electrical energy can be a form of
potential energy
Forms of Energy:
Sound Energy
• Sound is created by the
movement of air past the vocal
cords making them vibrate
• Sound energy is caused by an
objects vibrations
• Sound energy is a form of
potential and kinetic energy
Forms of Energy:
Light Energy
• Light energy is produced by the
vibrations of electrically
charged particles
Forms of Energy:
Nuclear Energy
• Nuclear energy is formed by
fusing nuclei or splitting them…
fusion or fission
Energy and Machines
• You transfer energy to the nutcracker
and it transfers energy to the walnut
• The nutcracker will not transfer more
energy to the walnut than you transfer
to the nutcracker
Energy and Machines
• Machines are energy converters
• When machines transfer energy,
energy conversions can often result
Let’s summarize
• What determines an objects
thermal energy?
An objects thermal energy depends on its
temperature, the arrangement of its
particles, and the number of particles in
the object
Let’s summarize
• Describe why chemical energy
is a form of potential energy.
When a substance forms, work is done to
bond particles of matter together. The
energy that creates the new bonds is
stored in the substance as potential
energy
Let’s summarize
• When you hit a nail into a board using a
hammer, the head of the nail gets warm.
IN TERMS OF KINETIC AND POTENTIAL
ENERGY, DESCRIBE WHY THIS HAPPENS.
The kinetic energy of the moving hammer
is transferred to the head of the nail,
causing particle sin the nail to move
faster. The faster the particles move, the
greater their thermal energy.
EQ #1 Explain the
relationship between
energy and work
• Energy is the ability to do work.
Work cannot occur without
energy
Let’s Review
When you bounce a basketball, you give it
kinetic energy. At the moment the ball hits
the ground, its kinetic, its kinetic energy
energy is greatest and its potential energy
is zero. At that moment, the change in the
shape that occurs when it hits the ground
gives the ball potential energy that is used
when the ball moves back upward. When
the ball bounces back up toward your hand
, its kinetic energy is converted into
potential energy because the position
changes. At the moment the ball is at the
top of its bounce, its kinetic energy is zero.
Why energy conversions
are important
• They make energy useful by converting
energy to a form of energy we can use
• Energy efficiency is a comparison to the
amount of energy before a conversion with
the amount of useful energy after a
conversion…efficiency means less waste
• Work input is always greater than work
output
Baseball hitting a bat