Transcript 5.2 – Conservation of Energy

5.2 – CONSERVATION
OF ENERGY
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
MECHANICAL ENERGY
• Energy due to the position and
motion of an object or objects in
a system
• mechanical energy = potential
energy + kinetic energy
MECHANICAL ENERGY
• the total amount of potential and
kinetic energy in a system
• Sum of KE + PE
• Bikes, Roller coasters, Swings, Rubber
Bands all involve Kinetic & Potential
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
=4C
IN-CLASS
ASSIGNMENT/HOMEWORK
• Continue working on Lecture Tutorial
1.
5.2 REINFORCEMENT
ANSWERS
– 29 PTS
2 pts Electrical
 Thermal
2.
2 pts Radiant/Light  Thermal
3.
3 pts CPE  Kinetic (thermal) AND Deputy = GPE sitting on
Horse
4.
5 pts Waiter = CPE  Kinetic AND Chandelier = GPE Electrical
 Light
5.
3 pts CPE  Kinetic  Sound  Kinetic  Electrical (CPE)
6.
5.2 REINFORCEMENT
ANSWERS
PTS
3 pts CPE 
thermal  Kinetic &–
PE 29
(mechanical)
7.
2 pts GPE  Kinetic  PE
8.
3 pts CPE  Mechanical (KE & PE)  Kinetic  GPE
9.
3 pts CPE  Kinetic  thermal (friction)
10. 3 pts CPE  thermal (friction)  Mechanical (KE & PE)