The Nature of Energy

1
The Nature of Energy

• Objectives
• How are work and energy related?
• What are the two basic kinds of energy?
• What are some of the different forms of energy?

2
Energy

• The ability to do work or cause change is called
  energy.
• Energy is measured in Joules.
• When an object does work on another object, it
  transfers some of its energy to the new object.
• Work is the transfer of energy.
• The object upon which work is done gains energy.

3
Types of Energy

• There are two main types of energy, kinetic
  energy (or energy of motion) and potential energy
  (or stored energy).

4
Kinetic Energy (KE)

• The kinetic energy of an object depends on its
  mass and velocity.
• The greater the mass and/or velocity, the greater
  the kinetic energy.
• Kinetic energy Mass x Velocity2
• 2
• Changing the velocity has a greater effect on
  kinetic energy than changing the mass. This is
  because the velocity is squared in the equation.
• Doubling the mass of an object will double the KE
  but doubling the velocity of an object will
  quadruple the KE.
• http//www.brainpop.com/science/energy/kineticener
  gy/

5
Potential Energy (PE)

• Potential energy is energy that is stored and
  held in readiness to do work.
• There are two types of potential energy, elastic
  and gravitational.

6
Elastic Potential Energy (EPE)

• Elastic potential energy is the PE associated
  with objects that can be stretched or compressed.
• Ex rubber bands, springs

7
Gravitational Potential Energy (GPE)

• Gravitational potential energy is the PE
  associated with changes in the height of an
  object.
• GPE Weight x Height
• Or
• GPE Mass x Acceleration due to Gravity x Height
• The greater the mass/weight of an object and the
  greater the height, the greater the GPE.
• http//www.brainpop.com/science/energy/potentialen
  ergy/

8
Forms of Energy

• Both kinetic and potential energy have a variety
  of different forms.
• Some of the major forms of energy are
  mechanical, thermal (heat), chemical, electrical,
  sound, light, electromagnetic, and nuclear.
• Can you think of any others?
• http//www.brainpop.com/science/energy/formsofener
  gy/

9
Mechanical Energy

• Mechanical energy is energy associated with the
  motion or position of an object.
• Mechanical energy can be either kinetic or
  potential.
• Mechanical energy potential energy kinetic
  energy
• Ex School bus ride, leaping frog

10
Thermal Energy

• Thermal energy is the total energy of all the
  particles in an object.
• Thermal energy can be either kinetic or
  potential.
• When the thermal energy of an object increases
  (thus increasing the temperature of the object,
  the particles that make up the object are moving
  faster.
• Q Which would have more thermal energy, ice or a
  glass of water?
• A A glass of water.

11
Chemical Energy

• Chemical compounds store chemical energy in the
  bonds that hold that compound together.
• Chemical energy is potential energy only.
• This energy is released when the bonds are broken
  and becomes another form of energy.
• Ex Food, lighting a match, wood

12
Electrical Energy

• Electrical energy is produced by moving
  electrical charges (electricity).
• Ex batteries, power lines

13
Electromagnetic (Sound and Light) Energy

• Electromagnetic energy is energy that travels in
  waves.
• These waves have both electrical and magnetic
  properties.
• Ex Radio waves, sound waves, microwaves, light
  waves, infrared waves, ultraviolet waves

14
Energy Conversion and Conservation

• Objectives
• How are different forms of energy related?
• What is the law of conservation of energy?

15
Energy Conversions

• A change from one form of energy to another is
  called an energy conversion.
• Any form of energy can be converted into any
  other form.
• Q Can you name some examples?
• A Toaster changing electrical energy to thermal
  energy, digestion converts the chemical energy in
  food to mechanical energy to move, thermal energy
  to stay warm, and electrical energy to think.

16
Nuclear Energy

• Nuclear Energy is the energy stored in the
  nucleus of an atom.
• Nuclear energy is potential energy that can be
  released and changed into another form of kinetic
  energy when the nucleus splits (nuclear fission)
  or the nucleus combines with another (nuclear
  fusion).
• Nuclear fission occurs in nuclear plants that
  make electricity.
• Nuclear fusion occurs in the sun and stars.
• http//www.brainpop.com/science/energy/nuclearener
  gy/

17
Energy Conversions

• Q What is the most common conversion of energy?
• A The conversion of potential energy to kinetic
  energy.
• Ex Soaring Straws Lab
• Potential Energy (Elastic) Stretched rubber band
• Kinetic Energy Releasing rubber band causing
  rocket to soar

18
Energy Conversions

• Sometimes, kinetic and potential energy have a
  cyclic relationship, varying between 100
  kinetic, a combination of both kinetic and
  potential, and 100 potential.
• Examples Juggling, bouncing ball, pendulum
• http//www.explorelearning.com/index.cfm?methodcR
  esource.dspViewResourceID390ClassID938997

19
Law of Conservation of Energy

• The Law of Conservation of Energy states that
  when one form of energy is converted to another,
  no energy is destroyed in the process. Energy
  cannot be created nor destroyed.
• The total amount of energy is the same before and
  after any process.

20
Law of Conservation of Energy

• Q So why does a Pendulum stop swinging?
• A A pendulum stops swinging because it transfers
  some of its mechanical kinetic energy to thermal
  energy as a result of friction. The friction of
  the air and on the attachment point of the string
  causes rubbing, which increases the motion of the
  atoms and increases thermal energy.

21
Law of Conservation of Energy

• Q Can you give another example of friction
  creating thermal energy?
• A Rubbing your hands together in the cold, the
  feet of runners, etc.
• Can you name another example of loosing energy to
  friction?
• A Rolling a toy car eventually stops, pushing a
  desk eventually stops, etc.

22
Law of Conservation of Energy

• The Law of Conservation of Energy DOES NOT equal
  conserving energy. Conserving energy means to
  save energy by not wasting it by doing such
  things as shutting the lights off when you are
  not in the room, carpooling, not letting the
  water run when you brush your teeth.
• Q What are some other ways to conserve energy?
• A Use low water toilets and washing machines,
  Unplug appliances when not in use, take public
  transportation, etc.

23
Review!

• Q Are energy and work the same thing?
• A Work and energy are NOT the same thing, even
  though they are measured in the same unit. As
  work is done, energy is transferred from one
  object to another.
• Q How are kinetic and potential energy
  different?
• A Kinetic energy is the energy of motion.
  Potential energy is stored energy that has the
  potential to do work.

24
Review!

• Q Name each form of energy and give an example
  of each.
• A Mechanical riding a bike
• Thermal hot water
• Chemical food
• Electrical batteries
• Electromagnetic visible light
• Nuclear fusion in a star

25
Review!

• Q A boulder that weighs 200N is poised at the
  edge of a 100 meter cliff. What is its
  gravitational potential energy? What is its GPE
  at 50m, 20m, and 10m?
• A GPE Weight x Height
• GPE 200N x 100m
• GPE 20,000J
• GPE Weight x Height
• GPE 200N x 50m
• GPE 10,000J
• GPE Weight x Height
• GPE 200N x 20m
• GPE 4,000J
• GPE Weight x Height
• GPE 200N x 10m
• GPE 2,000J

26
Review!

• Q What is energy conversion?
• A A change from one form of energy to another or
  an energy transformation.
• Q What is the law of conservation of energy in
  your own words?
• A The total energy before a process is the same
  as the total energy after.

27
Review!

• Q Describe the energy conversions that occur
  when a ball is dropped and bounces back up. Why
  do you think the ball bounces a little lower each
  time?
• A As it falls, potential energy changes to
  kinetics energy. As it bounces back up, kinetic
  energy is converted back to potential energy. The
  ball does not bounce as high because some energy
  escapes as thermal energy or sound (mechanical
  energy) when the ball hits the ground.

28
Review!

• Q A roller coaster car with a mass of 500kg is
  at the top of a hill that is 30m high. Without
  friction, what would its kinetic energy be as it
  reached the bottom of the hill?
• A Without friction, kinetic energy would be
  equal to the gravitational potential energy at
  the top of the hill.
• GPE Mass x Acceleration due to Gravity x
  Height
• GPE 500kg x 9.8m/s2 x 30m
• GPE 147,000J
• http//www.classzone.com/books/ml_sci_physical/pag
  e_build.cfm?idnoneu3