Transcript Conservation of Energy - Brunswick City Schools

Bellwork
• A large chunk of ice with a mass of 15-kg falls from a
roof 8.0-m above the ground. Find the KE and the speed
when it reaches the ground.
• What is the speed at the halfway point (@ 4 m)?
Conservation of Energy
As long as the system is closed so that objects do
not move in and out, and the system is isolated
from outside forces, then energy can only change
form.
Mechanical Energy
• In a system, it is the sum of KE + PE
depending on the situation.
• Can be all KE or all PE, or a combination of
both
• KE = 1/2 mv2
• GPE = mgh
• GPE is also written as Ug
• A 75-kg skier starts from rest at the top of a 45-m hill,
goes down the hill, then back up a 40-m hill. Both heights
are measured from the valley floor straight up. How fast
was the skier moving at the bottom of the valley? What is
the skier’s speed at the top of the next hill?
Remember the combustion
engine?
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Heat
Friction
Air resistance
Sound
Resisting/changing motion
Powering other mechanical parts
Kinds of Energy
•Mechanical – energy used to physically move things
•Radiant – light, radio, UV, etc.
•Electricity – electrical energy
•Heat/Thermal – energy moving from warmer to
colder things
•Chemical – energy of making and breaking chemical
bonds
•Nuclear – energy within the nucleus of an atom
[fusion/fission]
•Sound – energy of sound waves
Chemical
Potential
Nuclear
Electrical
Kinetic
Radiant
Sound
Heat/Thermal
Construct a scenario in which at least 6 of these energies are
used. Be creative! Label each energy transfer.
Example: Using a photovoltaic cell (radiant to electrical) to
power a fan (electrical to kinetic) that has a looped rope tied to
it spinning an electrical generator (kinetic to electrical) to
power a radio (electrical to sound).
To be collected at the end of class.