Conservation of Energy : Conservation of Energy “Location” of energy
The “paper trail” of energy transactions
Conservation of energy equation
Name a thing in real life that is made of pure energy. : Name a thing in real life that is made of pure energy.
Common Answers : Common Answers Lightning, Electricity, Sparks
Moving electrons, changing energy levels, giving off light.
Rainbows
Light shining through water mist.
Magnetic fields
Not a thing. Not made of anything. Nothing can be made of magnetic fields.
Fire
Vaporized hydrocarbons giving off light
Force Fields
Not real
Lasers
Light
Light
Particles called photons that carry the energy.
Nothing can be made of light. Light comes from the movement of charged matter.
Point: Energy doesn’t exist by itself. There has to be something there to have the energy.
Places of Energy : Places of Energy Type of Energy Object that can have that energy Verb (Plural) (Plural) (Singular)
Traces of Energy : Traces of Energy Goal: If “energy cannot be created or destroyed, only transferred,” we should be able to identify each of those transfers.
For each “transaction” give the original form of the energy, the new form of the energy, and how that energy was transferred.
For each form of energy, say what is storing the energy.
Gas Fireplace : Gas Fireplace What forms of energy are present?
Thermal Energy
Light Energy
Gas Fireplace : Gas Fireplace Trace the flow of energy back to its source.
Chemical potential energy in the natural gas converted into thermal energy and light by chemical reaction (burning).
initial form, final form, how it was transferred
Natural gas “fossil fuel” made from dead plants over millions of years. CPE in gas comes from heat and pressure underground and from CPE in the original plants.
If the energy flow branches, go one level deep on each branch, then follow the main branch to the end. Don’t have to follow all branches to the end.
Gas Fireplace : Gas Fireplace CPE in original plant material.
Pressure (weight of all the dirt on top of the plant material).
Done
Heat from the earth’s interior.
Done.
CPE in original plant material comes from photosynthesis with sunlight.
Gas Fireplace : Gas Fireplace In the sun
Light gets its energy from heat via “blackbody radiation”. (more on this later)
Nuclear reactions convert mass into thermal energy.
Mass is energy (at least, when your talking about nuclear reactions). It got its energy when it was created.
E = mc2
less obvious energy relations : less obvious energy relations Light is a form of energy carried by photons
Thermal energy is carried by particles of matter.
Blackbody radiation is the name for how thermal energy is transferred into light energy.
Nuclear reactions are how mass is converted into thermal energy.
Climber : Climber A mountain climber enjoys the view at the peak of Sharptop mountain.
What forms of energy has she gained while climbing? (note: “forms” is plural).
Trace the energy back to its source. (note: That morning she ate a big bowl of oatmeal.)
Mario and the Conservation of Energy Equation : Mario and the Conservation of Energy Equation Mario is sitting on a bomb when it goes off. The bomb has 1,0000 joules of CPE. 15% of that makes Mario fly and the rest of the energy makes other debris fly. Mario has a mass of 86 kg. How high does he go? Your job is to take notes about the steps I use to solve this problem.
By the numbers : By the numbers 1) Which forms of energy are changing?
GPE
KE
EPE
CPE
Wasted or Thermal 2) In your equation, include only the ones that are changing.
By the numbers : By the numbers 3) Then cross out any zeros 0 0 0 0 0
Dumb Idea. : Dumb Idea. During a football halftime show, an archer shoots an arrow straight up. His bow has a spring constant of 250 N/m and a draw of 80 cm. The arrow has a mass of 50 grams. At a height of 95 meters, the arrow strikes one of the blimps circling the stadium. How fast was it going when it hit?
Lost Penny : Lost Penny A penny (.002 kg) is dropped from the empire state building and falls 445 m to the sidewalk. It impacts with a speed of 60 mi/hr.
What percent of the energy was lost to air friction?
Go-Juice : Go-Juice Fuel can be rated by how much chemical potential energy per gallon it contains. For instance, burning one gallon of gasoline releases 1.3x10^8 Joules of energy.
Cars manage to convert 20% to 40% of that energy into motion.
The mpg of a car is an average. A car going a constant speed on a level road can get 120 mpg while the same car accelerating up a hill will get 2 mpg.
Hovercraft Design : Hovercraft Design A leaf-blower with a 0.5 horsepower engine is used to propel a home-made hovercraft. It doesn’t work very well. It takes 10 seconds to get the 80kg vehicle/rider up to 0.75 m/s. What percentage of the leaf-blower’s power went to propulsion and what percent when to churning up the air? 1 Hp = 745.7 J/sec
Fin : Fin
I shoot an arrow into the air… : I shoot an arrow into the air… An archer draws his bow and arrow back 65 cm, exerting an average force of 75 N. He holds it for a little while as he aims. He then fires the arrow horizontally at bail of hay, where it comes to rest half embedded in the hay.
How much work did the archer do on the bow while drawing it?
How much work did the archer do on the bow while aiming?
Did the archer do any work of any kind while aiming the bow? If so, on what?
Trace the flow of energy forward, from the moment the archer lets go, to the arrows final resting place.
Trace the flow of energy backward from the moment of release.
Tough One. : Tough One. You use a slingshot to launch a paintball at an opponent.
The slingshot has a spring constant of 200 N/m and you pull it back 65 cm.
It takes 0.4 seconds for the .05 kg ball to get there.
The ball looses 50 J to air resistance.
How fast is it going when it strikes the opponent?
List any assumptions you use along the way!
Where does that energy go after the impact?
Chugga-chugga : Chugga-chugga A specific car wastes 70% of the energy in its gasoline (assume this energy is turned into heat. “Q”). An engineer wants a car with a mass of 360kg to be able to reach 45 mi/hr (20 m/sec) going up a 3% incline in 7 seconds starting from rest. The engineer also knows this equation: d = v1t + ½at2. How much horsepower must the engine deliver? (Find the total Hp and the amount of Hp put into useful work.).
Conversion for Horsepower is 1 Hp = 745.7 J/sec
3% incline means rise of 3 ft for every 100 ft of run. 1.3x10^8 J/gal = 123,000 BTU/gal