Download Chapter 4 Section 2 Notes AIM: Describe how energy can be

Chapter 4 Section 2 Notes
AIM: Describe how energy can be transformed from one form to another
DO NOW:
1. Many devices can convert energy from one form to other forms. What devices convert
electrical energy to thermal energy?
ANSWER 1. a. alarm clock – sound
b. hair styler – heat or kinetic
c. toaster – heat
d. music – sound
e. video game – light
NOTES:
1. Fuel stores energy in the form of chemical potential energy.
2. The result of the transfer is chemical energy to thermal energy.
3. There are energy transfers that are less obvious because they do not result in visible
motion, sound, heat, or light.
* Examples:
- green plants convert light energy from the Sun into energy stored in chemical
bonds in the plants = photosynthesis
- chemical potential energy in food is transformed into other forms of energy by
your body = cellular respiration
AIM: Explain how the mechanical energy of a system is the sum of the kinetic energy and the
potential energy
DO NOW:
1. What is mechanical energy?
ANSWER a. The total amount of potential and kinetic energy in a system
b. Formula: ME = PE + KE
NOTES: (Look at text p. 108 – 111)
1. The total mechanical energy of any system never changes – it remains constant.
2. What happens to the mechanical energy of the apple as it falls from the tree?\
* Potential energy decreases while the kinetic energy increases. The total mechanical
energy remains constant.
3. Kinetic energy and GPE are converted into each other as a projectile rises and falls in its
curved motion/pathway (* See text p. 109).
* Swing discussion on p. 110-111
When you ride on a swing part of the fun is the feeling of almost falling as you drop from the
highest point to the lowest point of the swing’s path. The ride starts with a push that gets you
moving, giving you kinetic energy. As the swing rises, you lose speed but gain height.
In energy terms, kinetic energy changes to gravitational potential energy. At the top of your
path, potential energy is at its greatest. Then, as the swing accelerates downward, potential
energy changes to kinetic energy.
AIM: Discuss the Law of Conservation of Energy
NOTES:
1. The total amount of energy in a system never changes. The Law of Conservation of
Energy states that energy cannot be created or destroyed.
2. Sometimes it is difficult to see the Law of Conservation of Energy at work.
3. Friction and air resistance cause some of the mechanical energy of systems to change
forms.
4. Mass & Energy:
- Mass is converted into energy! The total amount of energy is still conserved if the
energy content of the masses involved are included.
o During fusion (joining together – takes place in the Sun and other stars), a
special type of energy conversion where a small amount of mass is transformed
into a tremendous amount of energy.
o Nuclear fission (breaking nuclei apart), converts a small amount of mass into
enormous quantities of energy.
* This process is used by nuclear power plants to generate electrical energy.
Ex: The Atomic Bomb in WWII!
5. The Human Body:
- Your body stores energy in the form of fat and other chemical compounds. This
energy is used to fuel the life processes to keep you alive.
o Maintaining a nearly constant internal temperature (homeostasis or dynamic
equilibrium)
o Your body gives off heat to its surroundings as well
 1 Calorie = 4,184 J of energy