Transcript Chapter 4: Energy

CHAPTER 4: ENERGY
SECTION 2: CONSERVATION OF ENERGY
WARM UP
• A 0.029 kg marble rolls down a ramp. At a height of
0.5 m, its velocity is 3 m/s.
• Find the GPE for the marble.
• Find KE for the marble.
TRANSFORMING ENERGY
• Energy can change
types – it can be
transformed
CAN YOU FIND THE ENERGY
TRANSFORMATION?
Electrical energy is converted to….
Electromagnetic energy (visible light energy) which is
converted to….
Mechanical energy (sound energy) which is converted
to….
Thermal energy (feel the back of TV or screen
sometime)
Chemical energy (from gasoline) is converted to…
Mechanical energy (engine starts working and moves
the car) which is converted to…
Sound energy, which is converted to….
Heat energy (don’t touch the engine!)
MECHANICAL ENERGY
• Mechanical Energy is the total amount of Kinetic
Energy and Potential Energy in a system
• A system is a group of objects that work together
MECHANICAL ENERGY
ME = KE + PE
ME = ½ mv2 + mgh
MECHANICAL ENERGY
• For a falling object:
• GPE decreases because height decreases
• KE increases because gravity increases v
MECHANICAL ENERGY
• What is the mechanical energy of a 75 kg man on a
diving board 10 m above the ground?
• The man jumps. After he has fallen 5 m, he is
traveling about 9.9 m/s. Find the mechanical
energy of the man.
LAW OF CONSERVATION OF ENERGY
• Law of
Conservation of
Energy:
• Energy is never
created or
destroyed,
only transferred or
transformed
* The total amount of energy in a closed
system never changes
CONSERVATION OF ENERGY
• Why do we lose mechanical energy?
• Friction changes kinetic energy to heat energy,
which is lost to the surroundings
LOSING KINETIC ENERGY TO FRICTION