The Law of Conservation of Energy

1
(No Transcript)
2
The Law of Conservation of Energy

• Energy cannot be created or destroyed it may be
  transformed from one form into another, but the
  total amount of energy never changes.

3
What is energy?

• the ability to do work
• The combination of energy and matter make up the
  universe
• Matter is substance, and energy is the mover of
  substance.

4
Energy is natures way of keeping score.

• We sense energy only when the score changes,
• either a transformation from one form of energy
  to another,
• or a transfer of energy from one point to
  another.

5
How is all energy divided?
All Energy
6
Potential Kinetic

• energy of position or energy in storage.
• Water behind a dam
• Hammer over head
• Food on the plate

• energy of motion, the form capable of doing work
• Flowing water
• A falling hammer
• Electrons regenerating ATP in a biol cell

7
PE mgh

• m mass (kg)
• h height (m)
• g accel due to gravity
• (9.8 m/s2)

8
Kinetic Energy

• KE of an object depends upon two variables
• the mass (m) of the object
• the speed (v) of the object.

9
What is Gravitational Potential Energy?

• Potential energy due to an objects position
• P.E. mass x
• height x gravity

Dont look down, Rover! Good boy!
10
Gravitational Potential Energy

• GPE is the energy stored in an object as the
  result of its vertical position (i.e., height).
• Amount of GPE is dependent on two variables
• the mass
• the height

11
Calculating Gravitational Potential Energy
GPE mgh
(rate an object falls due to gravity) g
9.8m/sec2
12
What is Potential Energy?

• Energy that is stored and waiting to be used later

13
What is Elastic Potential Energy?

• Potential energy due compression or expansion of
  an elastic object.

Notice the ball compressing and expanding
14
What is Chemical Potential Energy?

• Potential energy stored within the chemical bonds
  of an object

15
What is Kinetic Energy?

• Energy an object has due to its motion
• K.E. .5(mass x speed2)

16
KE 1/2 m v2

• .25 kg baseball
• at 50 m/s
• .5 (.25kg) (50 m/s)2
• 312 J

• 4 kg bowling ball
• at 10 m/s
• .5 (4kg) (10m/s)2
• 200 J

17
Kinetic Energy
The greater the mass or velocity of a moving
object, the more kinetic energy it has.
18
Courtesy Jerry Ohlingers Movie Material Store
Work is done when a force is exerted over a
distance.
19
Work

• is equal to the force that is exerted times the
  distance over which it is exerted.
• W F x d
• The unit of work combines the unit of force (N)
  with the unit of distance (m)
• Newton-meter (N-m) aka Joule.

20
You carry a 20 kg suitcase upstairs, a distance
of 4m. How much work did you do?

• W F x d
• F ma
• (20 kg) (10m/s2) 200 N
• W F x d
• (200 N) (4m)
• 800 J

21
Power

• measures the rate of work done.
• or the rate at which energy is expended.
• Power is the amount of work done, divided by the
  time it takes to do it.
• Power (watts) work (joules) / time (sec)
• P W/t

22
Power

• Since work performed equals energy expended,
• Power (watts) energy (joules) / time (sec)
• The watt is defined as the expenditure of
• 1 joule of energy in 1 second.
• (75 watt light bulb consumes 75 J/sec)

23
Important formulas and units

• Quantity Definition Units
• Force mass x accel. newtons
• Work force x distance joules
• Energy power x time joules
• Power work / time watts

24
Ex. Problem on Power

• Your CD system, uses 250 watts of electrical
  power.
• You play it for 3 hrs. How much energy used?
  About how much would it cost? If one kWh is .08.
• Energy (J) power (watts) x time (sec) (250w)
  (3hr) 750 Whr .75 kWh
• The cost 8 cents/ kWh x .75 kWh
• 6 cents

25
Power work / time

• . Two physics students, Will N. Andable and Ben
  Pumpiniron, are in the weightlifting room. Will
  lifts the 100-pound barbell over his head 10
  times in one minute Ben lifts the 100-pound
  barbell over his head 10 times in 10 seconds.
  Which student does the most work? Which student
  delivers the most power?

26
Mechanical Advantage

• The number of times a machine multiplies your
  effort force.
• Example If you push on the handle of a car jack
  with a force of 30 lbs and the jack lifts a 3000
  lb car, what is the jacks mechanical advantage?
• The jack multiplies your effort force by 100
  times.

27
There are 2 types of mechanical advantage.

• IMA Ideal mechanical advantage.
• This is the number of times a machine is designed
  to multiply your effort force.
• It is based on measurements of the machine.
• Ignores friction

• AMA Actual mechanical advantage
• This is the number of times the machine actually
  multiplies your effort force.
• AMA resistance force/effort force.
• Includes the effects of friction

IMA is always greater than AMA.
28
Mechanical Advantage

• Mechanical advantage is the ratio of output force
  divided by input force. If the output force is
  bigger than the input force, a machine has a
  mechanical advantage greater than one.
• If a machine increases an input force of 10
  pounds to an output force of 100 pounds, the
  machine has a mechanical advantage (MA) of 10.
• In machines that increase distance instead of
  force, the MA is the ratio of the output distance
  and input distance.
• MA output/input

29
Drawing Conclusions

• Two divers of equal mass about to dive
• Diver A has gt Potential Energy than B
• Compare divers positions
• Which diver will hit water _at_ highest speed
• What happens to energy when diver enters the
  water?

30
Diver A
Fastest
Diver B
31
6 fundamental forms of energy

• mechanical energy
• Thermal (heat) energy
• electromagnetic energy
• electrical energy
• nuclear energy
• chemical energy

32
What is the source of our energy?

• The source of practically all our energy is the
  Sun.

33
What is Mechanical Energy?

• Energy due to a objects motion (kinetic) or
  position (potential).
• The bowling ball has mechanical energy.
• When the ball strikes the pins, mechanical energy
  is transferred to the pins!

34
Mechanical Energy
Mechanical energy is the movement of machine
parts. Mechanical energy comes from the motion
(kinetic energy) and position (potential energy)
of objects. EXAMPLES Wind-up toys, grandfather
clocks, and pogo sticks Wind power uses
mechanical energy to help create electricity.
Potential energy Kinetic energy Mechanical
energy
35
Examples of Mechanical Energy
36
What is ElectromagneticEnergy?

• Light energy
• Includes energy from gamma rays, xrays,
  ultraviolet rays, visible light, infrared rays,
  microwave and radio bands

37
What is Electrical Energy?

• Energy caused by the movement of electrons
• Easily transported through power lines and
  converted into other forms of energy

38
Electrical Energy
Electrical energy is the movement of electrons.
Examples Lightning and static electricity
occur naturally. Science hasn't found a way to
use natural forms of electrical energy. We use
different energy sources to create electrical
energy by using generators and turbines.
39
(No Transcript)
40
What is Chemical Energy?

• Energy that is available for release from
  chemical reactions.
• The chemical bonds in a matchstick store energy
  that is transformed into thermal energy when the
  match is struck.

41
Examples of Chemical Energy
42
Chemical Energy
Chemical energy is the energy stored in the bonds
of atoms and molecules. This a form of potential
energy until the bonds are broken.
Examples Fossil fuels store chemical energy.
Products that contain chemical energy
include TNT, baking soda, and a match.
Biomass, petroleum, natural gas, propane and coal
are examples of stored chemical energy.
43
What is Thermal Energy?

• Heat energy
• The heat energy of an object determines how
  active its atoms are.
• A hot object is one whose atoms and molecules are
  excited and show rapid movement.
• A cooler object's molecules and atoms will show
  less movement.

44
Thermal Energy
Thermal energy is the internal energy in
substances - the vibration and movement of atoms
and molecules within substance. Thermal energy
is created in the movement of atoms.
EXAMPLES Boiling water, burning wood, and
rubbing your hands together really fast.
Geothermal and passive solar are sources of heat
energy.
45
Nuclear Energy
Nuclear energy is the energy stored in the
nucleus of an atom. Nuclear energy is unusual in
that it can give off energy in
the form of light or
heat, but it is the change in the atom's
makeup that produces the energy.
46
Nuclear Energy
All power plants convert heat into electricity
using steam. At nuclear power plants, the heat
to make the steam is created when atoms split-
fission. Fission takes place when the nucleus
of a heavy atom like plutonium or uranium is
split into two when struck by a neutron. This
releases more neutrons which repeat the process
and releases more nuclear energy (heat). This
heat boils water and creates steam that turns a
turbine. As a turbine spins, the generator turns
and its magnetic field produces electricity that
goes to your house.
47
(No Transcript)
48
QUIZ TIME!

• What type of energy cooks food in a microwave
  oven?
• ELECTROMAGNETIC ENERGY
• What type of energy is the spinning plate inside
  of a microwave oven?
• MECHANICAL ENERGY

49
QUIZ TIME!

• Electrical energy is transported to your house
  through power lines.
• When you plug an electric fan to a power outlet,
  electrical energy is transform into what type of
  energy?
• MECHANICAL ENERGY

50
QUIZ TIME!

• What energy transformation occurs when an
  electric lamp is turned on?
• ELECTRICAL ENERGY
• ?
• ELECTROMAGNETIC ENERGY

51
What types of energy are shown below?

• Mechanical and Thermal Energy
• (Dont forget friction)

52
What type of energy is shown below?

• Chemical Energy

53
What types of energy are shown below?

• Electrical, Mechanical and
• Electromagnetic Energy

54
What type of energy is shown below?

• Chemical Energy (yummy)

55
What type of energy is shown below?

• Thermal Energy

56
What types of energy are shown below?

• Mechanical, Electromagnetic, Electrical, Chemical
  and Thermal Energy

57
The Law of Conservation of Energy

• Energy cannot be created or destroyed it may be
  transformed from one form into another, but the
  total amount of energy never changes.