Chapter 9 Energy and Energy Resources

1
Chapter 9Energy and Energy Resources

• Section 1
• What is Energy?

2
Energy and Work- Working 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)

3
Kinetic Energy is Energy of Motion

• An object which has motion-whether 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

4
Potential Energy Is Energy of Position

• Potential energy is the energy an object has
  because of its position or shape.

5
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 its usual shape

6
Potential Energy Is Energy of Position

• A rubber band is another good example of
  potential energy.

No energy
potential energy
7

• 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.

8

• 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.

9
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.
10
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

11
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

12
Forms of EnergyElectrical 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

13
Forms of EnergySound 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

14
Forms of EnergyLight Energy

• Light energy is produced by the vibrations of
  electrically charged particles

15
Forms of EnergyNuclear Energy

• Nuclear energy is formed by fusing nuclei or
  splitting them
• fusion or fission

16
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

17
Energy and Machines

• Machines are energy converters
• When machines transfer energy, energy conversions
  can often result

18
Lets 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
19
Lets 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
20
Lets 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.
21
EQ 1 Explain the relationship between energy
and work

• Energy is the ability to do work. Work cannot
  occur without energy

22
Lets 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.
23
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 conversionefficiency means
  less waste
• Work input is always greater than work output

24
Baseball hitting a bat