ch 4 energy
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Ch 4 Energy. Sec 1 The Nature of Energy. Energy (E) is the ability to do work to cause change Many forms: radiant, electrical, chemical, thermal, nuclear Basic unit of E is the joule (J) named for British scientist Prescott Joule Usually when you think of E, you think of ACTION!! - PowerPoint PPT PresentationTRANSCRIPT
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Ch 4 EnergyCh 4 Energy
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Sec 1 The Nature of Energy
Energy (E) is the ability to do work to cause change
Many forms: radiant, electrical, chemical, thermal, nuclear
Basic unit of E is the joule (J) named for British scientist Prescott Joule
Usually when you think of E, you think of ACTION!!
The E that involves motion is Kinetic E (KE)
Amount depends on the mass and the velocity of the object
Semi truck going 100 km/hr has more KE than a motorcycle also going 100 km/hr
Identical vehicles—the faster has more KE
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KE KE Equation KE = ½ m x v2
m= mass in kg v= velocity in m/s Let’s try one! A soccer ball with a mass
of .5 kg is moving at a velocity of 20.0 m/s. What is the soccer ball’s KE?
1. KE = ½ m x v2
2. m= .5 kg v= 20.0 m/s 3. KE= ½(.5)(20)2
4. KE= 100 J
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Whiteboard Whiteboard Practice!!Practice!!
A jogger has a mass of 75.0 kg and is jogging at a speed of 2.0 m/s. What is the jogger’s KE?
A race car is speeding around a track at 48.0 m/s. The mass of the car and driver is 560.0 kg. What is the car’s KE?
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Potential Energy (PE)
E that does not involve motion is stored energy
Amount depends on the position of the object above Earth-this type is called gravitational potential energy or GPE
Also the condition of the object—relaxed spring has less PE than a tightly coiled spring
This type called elastic potential energy (EPE)
PE can also be stored in foods, fuels and dry cell batteries—chemical potential energy (CPE)
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GPE= mghm= mass (kg) g= 9.8m/s2 h= height (m)
1. Your text book has a mass of 1.5 kg and is sitting on the top of your locker 1.75 m above the floor. What is its GPE?
2. An 65.0 kg cliff diver is ready to jump. The cliff is 15.0 m above the water. What is the diver’s GPE?
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Sec 2 Law of Conservation of E
E cannot be created or destroyedE cannot be created or destroyed E can change form E can change form from one type of E to another (KE one type of E to another (KE
to PE) but it is never destroyedto PE) but it is never destroyed Total amount of E in the universe stays constantTotal amount of E in the universe stays constant
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E conversions
An incandescent lightbulb transforms electrical E into light and thermal E
Green plants convert light E from Sun into chemical E
Engines change the chemical PE in gasoline into KE of moving vehicles
Mechanical energy (ME) is KE + PE
There is no change in ME when PE changes into KE or KE into PE
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Nuclear fission and fusion Fission is when the
nuclei of an atom is broken apart
Nuclear power plants generate electrical E this way
Fusion is when nuclei of hydrogen isotopes come together to make a helium atom—happens in our Sun and other stars