1. 5.2 – Conservation of Energy

2. 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.

3. Changing Forms of Energy
Light bulb  Light & Heat
Electrical  Radiant & Thermal

4. Changing Forms of Energy
Fuel  Moving Car
Chemical Potential  Thermal
Electric spark ignites fuel
Thermal Kinetic
Gases expand and move parts of engine

5. 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

6. mechanical energy = potential energy + kinetic energy
Energy due to the position and motion of an object or objects in a system
mechanical energy = potential energy + kinetic energy

7. 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

8. 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

9. 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

10. Swing Push gets you moving Swing rises & loses speed
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

11. 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

12. 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

13. 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.

14. Nuclear Fission
Splitting of one large nucleus into 2 or more smaller nuclei
Power Plants create electrical energy using fission

16. 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

17. 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

18. Chemical Potential Energy 1 food Calorie (C) = 4,184 Joules
Food Energy
Chemical Potential Energy
1 food Calorie (C) = 4,184 Joules
1 gram fat = 9 Calories
1 gram of carbohydrates & proteins = 4 C

19. In-Class Assignment/Homework
Continue working on Lecture Tutorial

20. 5.2 reinforcement Answers – 29 pts
2 pts Electrical  Thermal
2 pts Radiant/Light  Thermal
3 pts CPE  Kinetic (thermal) AND Deputy = GPE sitting on Horse
5 pts Waiter = CPE  Kinetic AND Chandelier = GPE Electrical  Light
3 pts CPE  Kinetic  Sound  Kinetic  Electrical (CPE)

21. 5.2 reinforcement Answers – 29 pts
3 pts CPE  thermal  Kinetic & PE (mechanical)
2 pts GPE  Kinetic  PE
3 pts CPE  Mechanical (KE & PE)  Kinetic  GPE
3 pts CPE  Kinetic  thermal (friction)
3 pts CPE  thermal (friction)  Mechanical (KE & PE)