Concepts in Action Chapter 15

1
Concepts in ActionChapter 15

• A summary discussion with author Wysession and
  Malley

2
Energy

• Recall that energy is the ability to do work.
• Recall that energy is always transferred when
  work is done.
• Recall that there are several forms of energy
• Energy is constantly being transformed from one
  form to another
• BUT!!!!

3
THE LAW SAYS

• There is a law in nature
• It says that no matter what, the total amount of
  energy in the universe NEVER changes!!
• Energy is NEVER created nor destroyed.
• The energy in the universe today is exactly the
  same amount of energy that was in the universe at
  the beginning of time and it will be the same at
  the end of time!!!

4
You cant.

• You cannot create energy nor destroy it
• BUT
• You CAN transform energy from one type to
  another
• Example
• You eat lunchfood.chemical energy
• That energy is stored until you convert it to
  mechanical energy when you run down the street
• That energy, mechanical energy, is then converted
  to heatyoure hotter, the air is warmer , the
  pavement is warmer, the bottom of your shoes are
  warmer, etc.

5
YOU CAN.

• We can burn coal in a power plantchemical energy
  which is converted to electrical energy so now
  you can turn on your TV and that electrical
  energy is converted to sound energy and light
  energy.
• Energy cannot be made or lost but it can be
  converted into different forms..
• UNTIL
• Eventually, all forms of energy will be converted
  to HEAT.

6
HEAT DEATH

• Eventually all forms of energy, heat light sound
  electric chemical nuclear etcall forms will
  eventually be transformed into heat
• Just rubbing your hands together brings us closer
  to heat death
• In the universe, eventually there will be no
  planets, no stars, no light, no soundjust HEAT!!
• When that happens we call that maximum entropy,
  maximum chaosthe universe is now DEAD

7
Classify

• Humans love to organize and classify and
  categorize in order to understand Nature
• So, most types of energy can be calssified into
  two big groups
• Energy stored up due to work done to change the
  position of the object, called potential energy
• Energy being used, the energy of motion called
  kinetic energy.
• We will always use the initials PE for potential
  energy and KE for kinetic energy.

8
PE

• Work was done on a system
• A system is an oft-used term which means that
  portion of the universe that is of interest to us
  at the moment. For convenience we can isolate a
  system from influences out there in the rest of
  the universe.
• So, we do work on a system
• We lift a book, stretch a rubber band, compress a
  springwe have done something to alter the
  position of parts of the system, we have made the
  system LESS stable because we gave it some
  energy..
• High energy systems are less stable than low
  energy systems
• But until the system is released from this
  higher tension condition, it is work that is
  stored up just waiting to be used.
• In order for the PE to convert to KE it will have
  to release the energy given to it when work was
  done on it. The system will have to move. The
  system will have to lower its energy level and
  become more stable.

9
We can calculate

• Because PE is about changing the position of the
  parts of a system, we must have a frame of
  reference in order to measure, quantify the
  amount of PE a system has gained.
• PE mgh
• PE mgs
• PE mass times gravity times the amount of change
  in position measures the gain in PE. H height
  from some frame of reference or just some s,
  displacement from some frame of reference.
• The unit used to measure ALL forms of energy is
  the Joule.
• A 10 kg mass is lifted up 4m off the floor. What
  is the amount of energy stored up in that mass?
• PE 10kgx9.8m/s/sx4m ??

10
You can always count on Mother Nature

• There is one rule you can put into your back
  pocket and bring out to answer all kinds of
  questions about WHY things happen in Nature.
• The rule is
• NATURE ALWAYS SEEKS STABILITY.
• All kinds of things happen in Nature because
  Nature wants systems to always seek the most
  stable condition possible.
• FOR EXAMPLE!!!!!
• All of chemistry operates because of this rule.
  Atoms join together to form molecules of new
  substances so that the atoms become more stable
  in that they try to gain full outer energy
  levelsthey want 8 electrons facing the world.
  Work is done and stored up for us to break up and
  release that stored up chemical energy when we
  digest food or burn fuel.

11
KE

• This is the energy of motion, this is energy
  being usedno longer stored up!!
• Like PE it must be measured against some frame of
  reference
• We can measure the amount of Kinetic Energy a
  system has using an equation
• KE ½ M V2
• The unit of course is still the Joule!!!
• So a 10 kg girl is running at 2 m/s. What is her
  KE???

12
E M C2

• Mass is really condensed energy!!
• So taught Albert Einstein in his famous equation.
• This is best made use of in nuclear powerduring
  fission or fusion reactions matter is
  destroyedmatter is converted into pure energy!!
• A very small amount of matter can light a city
  for years!!!

13
Resources

• Nuclear energy has its drawbacksbut so far, so
  does EVERY form of fuel we need to operate our
  lifestyles. Try considering a day without ANY
  electricity, for exampleyou couldnt even ride
  in a car since electricity starts that babyno
  lights, no music, it might be a pretty tough day
• Lets face it, we like out electricity!!
• But we dont like the pollution created in
  generating electricity, we dont like the global
  warming that seems to be the case because of the
  conversion of so much energy into heat
• Among other causes of raising global temperatures.

14
Renewable vs nonrenewable

• Nonrenewable energy sources are those we dig out
  of the ground
• Coal, oil, uranium, gas
• These take so long to formmillions of yearsthat
  in reality, once they are used uptheyre gone!
• Renewable energy sources are those derived over
  shorter periods of timemore easily renewed
• Biomasses like wood or solar energy, wind, tidal
  energy, hydroelectric energy.
• No matter how, the truth is, we need sources of
  energy that will do work for us!!!