Download 5.2 – Conservation of Energy

5.2 – Conservation of Energy
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Objectives
Describe how energy can be
transformed from one form to another.
 Explain how the mechanical energy of
system is the sum of the potential and
the kinetic energies.
 Discuss the law of conservation of
energy.

Changing Forms of Energy

Light bulb  Light & Heat

Electrical  Radiant & Thermal
Changing Forms of Energy

Fuel  Moving Car

Chemical Potential  Thermal


Electric spark ignites fuel
Thermal Kinetic

Gases expand and move parts of
engine
Less Obvious Changes

Green plants convert sunlight into energy
stored in chemical bonds

Eating corn (chemical potential energy)
becomes other forms of energy in your
body
Kinetic & Potential Energy
Mechanical energy is the total
amount of potential and kinetic energy
in a system

Bikes, Roller coasters, Swings, Rubber
Bands all involve Kinetic & Potential
Energy
Mechanical Energy
Energy due to the position and motion
of an object or objects in a system
mechanical energy = potential energy + kinetic energy
Falling Objects
Object has gravitational potential energy
due to Earth pulling it down
 Object becomes loose and accelerates
downward due to gravity

Loses gravitational potential energy
 Transformed into kinetic energy as speed
increases

Projectile

Kinetic & Gravitational Potential Energy are
converted between each other as ball rises and
falls




Kinetic Energy gets ball moving
Kinetic Energy converted into GPE as ball rises
GPE greatest at peak of path
GPE converted back to Kinetic Energy as it moves
downward and increases speed
Swing
• Push gets you moving
• KINETIC ENERGY
• Swing rises & loses speed
• Kinetic changes into GRAVITATIONAL POTENTIAL
ENERGY
• Greatest at top of path
• Swing accelerates downward
• GPE changes into KINETIC ENERGY
Law of Conservation of Energy
Energy cannot be created or destroyed
 Energy simply changes from one form to
another, but total amount of energy
never changes

Why don’t we always see conservation?

Friction & Air Resistance cause
mechanical energy to be converted into
thermal energy

That’s why chains get hot on a swing
Energy not created
or destroyed, but
changed into a
new form

Nuclear Fusion
Sun’s energy  Light & Heat on Earth
 Small amount of mass is transformed
into tremendous amount of energy
 Combining of 2 or
more small nuclei into
one larger nucleus

In the reaction shown here,
the nuclei of the hydrogen
isotopes deuterium and
tritium undergo fusion.
Nuclear Fission
Splitting of one large nucleus into 2 or
more smaller nuclei
 Power Plants create electrical energy
using fission

Human Body

Chemical Potential Energy maintains
body temperature


Excess given off as heat to environment
CPE fuels processes such as heart beat
and food digestion

Energy is converted into heat and
movement
Human Body

Obeys Law of Conservation
of Energy

To maintain a healthy weight
you must have a balance
between energy consumed
and energy used

Excess energy can be stored
as fat
Food Energy
Chemical Potential Energy
 1 food Calorie (C) = 4,184 Joules

1 gram fat = 9 Calories
 1 gram of carbohydrates & proteins = 4 C

In-Class Assignment/Homework

5.2 WKT