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Ch 4 Energy

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!!

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Ch 4 Energy

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  1. Ch 4 Energy

  2. 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

  3. 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

  4. Whiteboard 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?

  5. 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)

  6. 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?

  7. Sec 2 Law of Conservation of E • E cannot be created or destroyed • E can change form from one type of E to another (KE to PE) but it is never destroyed • Total amount of E in the universe stays constant

  8. 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

  9. 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

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