15.2 Energy Conversion and Conservation
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Transcript of 15.2 Energy Conversion and Conservation
15.2 Energy Conversion and Conservation
Page 453-459
Energy ConversionEnergy can be CONVERTED from one form to anotherThe process of changing energy from one form to anotherEx: When a spring unwinds goes from Elastic Potential Energy TO Kinetic EnergyLight bulb: Electric (the battery creates electricity) TO Thermal and Electromagnetic (heat of the bulb and the light it shines)
Energy conversion examples
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Chemical energy (in battery)
Electrical energy (through the wires)
Electrical energy (from the wall socket to the electric stove)
Electromagnetic and thermal energy (from the light bulb)
Thermal energy (the hot stove coil)
Law of Conservation of EnergyThe law of conservation of energy states that Energy cannot be created or destroyedIn a closed system (where nothing can enter or leave) the amount of energy present at the beginning of a process is the same as the amount of energy at the endTherefore, the pendulum in the picture would always reach the exact same height on either side and would never come to rest
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Law of Conservation of Energy (cont.)
In the real world, energy can be lost to frictional forces (kinetic to thermal energy which is then lost) If you account for thermal energy lost to friction energy will be conserved overallFriction can slow thingsSo the pendulum would eventually stop moving QuickTime™ and a
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Friction effects machineryFriction within machinery reduces efficiencyFriction is a major cause of energy consumption in cars and factories because all the moving parts are subject to frictionYou can reduce friction but you cant avoid it.
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Engine block over heating can be caused by excess friction. If a lot of energy is lost as heat more fuel is needed to do less work.
Energy Conversion
The GPE of an object is converted to KE of motion as it falls.Ex: Clock Pendulum
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Energy Conversion: gull vs oysterSea gulls use PE to obtain foodAs the gull brings the oyster up into the air PE increasesAt its highest point the gull releases the oyster at max PEAs it falls PE is converted to KE as the oyster increases is velocity toward the rocksAs it hits the rocks the oyster is at max KE and it shatters into the gulls lunch
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Energy Conversion: pole vault
Pole-vaulter sprints = kinetic energy
Pole bends = elastic potential energy
Pole springs back into shape = kinetic energy
Pole-vaulter rises quickly into the air = kinetic to gravitational potential energy
Reaches highest point and begins to fall, max PE to KE
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http://www.popsci.com/how-it-works/article/2008-07/how-it-works-pole-vault
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Energy Conversion CalculationsMechanical energy = KE + PE
When friction is small enough to be ignored mechanical energy at the beginning equals the mechanical energy at the end which means mechanical energy remains constant
Conservation of Mechanical Energy (KE + PE)begin = (KE + PE)end
Conservation of mechanical energy problemAt a construction site, a 1.5 kg brick is dropped from rest and hits the ground at a speed of 26 m/s. assuming air resistance can be ignored, calculate the GPE of the brick BEFORE it was dropped.Given info:
Mass = 1.5 kgVelocity = 26 m/s
But we know thatKEb + PEb = KEend + PEend
So if….. KEb= 0 and PEend = 0
Then… 0 + Peb = KEend + 0
And finally…. PEb = KEend
So we solve for KEend to find PEb
KEend = 1/2 mv2
KEend = 1/2 (1.5 kg) (26m/s)2
KEend = 1/2 (1.5 kg) 676 m2/s2
KEend = 507 kgm/s2m
KEend = 507 N m
KEend = 507 J
So now we know KEend therefore we also know PEb
PEb = KEend = 507 J, so PEb = 507 J
Cannot find PE with only this info
Step 3
Step 2
Step 1
Final answer
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Energy and Mass
Einstein’s equation, E = mc2, says that energy and mass are equivalent and can be converted into each other
Meaning energy is released as matter is destroyed, and matter can be created from energy
Therefore, the law of conservation of energy has been modified to say that mass and energy together are always conserved.
E = mc2
m = mass and C = speed of light
The End
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