of energy notes: the law of conservation -...
TRANSCRIPT
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Notes: The Law of Conservation of Energy
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The Law of Conservation of Energy
▪ The Law of Conservation of Energy states that energy cannot be created or destroyed.
▪ It just changes forms▪ The big picture… the total energy in the
universe remains constant.
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KE and PE
▪ In many situations, there is a change between potential and kinetic energy.
▪ The total amount of potential and kinetic energy in a system is called the mechanical energy
▪ Mechanical energy = PE + KE
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Mechanical Energy
▪ Mechanical energy is due to the position and motion of the object.
▪ What happens to the mechanical energy of an apple as it falls from a tree?
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Mechanical Energy
▪ As the apple falls to the ground, its height decreases. Therefore, its Gravitational PE decreases.
▪ The potential energy is not lost… it is converted into kinetic energy as the velocity of the apple increases.
▪ What happens to the mechanical energy?
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Mechanical Energy
▪ The mechanical energy does not change because the loss in potential energy is simply transferred into kinetic energy.
▪ The energy in the system remains constant!!
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Swinging Along
▪ Think about the changes in energy when you are on a swing…
▪ At what point do you have the most potential energy?
▪ At what point do you have the most kinetic energy?
▪ What happens to the mechanical energy?
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▪ But how? If I stop pumping while I’m swinging, I stop!! So, where’s the energy?
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Conservation of Energy
▪ You need to remember friction… (the action of one object or surface rubbing against another)
▪ As you slow down on the swing, the hooks and the chain rub against each other and air pushes against the rider.
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▪ Friction causes some of the mechanical energy of the swing to change to thermal energy and the temperature of the hooks and chain heat up a little.
▪ The energy is still there, just in a different form!!
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Conservation of Energy
▪ Energy is transformed… not destroyed!!
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Energy in Your Body
▪ Even the energy converted in your body follows the law of conservation of energy.
▪ Chemical potential energy is transferred to kinetic energy that allows your body to move!!
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Calories…
▪ A Calorie (C) is a unit to measure energy in foods
▪ 1 Calorie is equal to about 4,184 Joules.
▪ A person uses about:▪ 55 Calories while sleeping for 1 hour▪ 210 Calories while walking for 1 hour▪ 850 Calories while running for 1 hour
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Changing Forms of Energy
▪ Energy is most noticeable as it transforms from one type to another.
▪ What are some examples of transforming electrical energy?▪ A lightbulb▪ A hair dryer
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Changing forms of Energy
▪ An example of transforming chemical energy is a car engine. Chemical potential energy in gasoline is transformed into kinetic energy of the car as it moves!!