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andand Work Work
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What is energy?What is energy?•Ability to make something happen
•Or work to happen
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Potential and Potential and Kinetic EnergyKinetic Energy
• Potential energy is energy that is stored in an object.
• Kinetic energy is energy of motion.
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Potential energyPotential energy• Potential energy (P.E.) is the ability
of an object to do work because of its position. work done by the object = P.E. lost
• work done on the object = P.E. gained.
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Potential energyPotential energy• Potential energy is a type of energy
that is "hidden" in some way. It is a type of energy that can be converted to other forms and often is related to some attractive or pushing forces.
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TypesTypes• Elastic Potential Energy
– Anything that can act like a spring or a rubber band can have elastic potential energy.
– Let's take the rubber band or a spring– Wind up toys store energy this way
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Gravitational Potential Gravitational Potential EnergyEnergy
• There is a constant attractive force between the Earth and everything surrounding it, due to gravity.
• To lift something off the ground it takes energy, so just by lifting an object, that object now has higher gravitational potential energy.
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• Gravitational potential energy is typically converted into kinetic energy (an object falling) before it is converted into any other type of energy.
• Hydroelectric power is generated this way. As the water falls, it turns a turbine, which pushes electrons around, creating an
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Changing GPEChanging GPE• What does it depend on?
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Chemical Potential EnergyChemical Potential Energy
• A chemical bond can be thought of as an attractive force between atoms.
• Because of this, atoms and molecules can have chemical potential energy.
• Anytime two atoms form a strong covalent or ionic bond or two molecules form a chemical energy is converted into other forms of energy, usually in the form of heat and light.
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• Strong bonds have low chemical energy and weak bonds have high chemical energy.
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Kinetic energy is the energy Kinetic energy is the energy of motion.of motion.
• Any object that is moving has kinetic energy. • Ball Moving Horizontally• Kinetic Energy Equation
• m = mass (in kg), v = velocity (in m/s), and KE = kinetic energy (in J = joules).
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• Remember, the units for energy are Joules - Kilogram . meters / sec2
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• Practice Problems: • 1. A 12 pound bowling ball is held 20
feet above the floor. Calculate its GPE.
• 2. A 2kg object is traveling at 4m/s. Calculate its KE.
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• Law of Conservation of Matter and Energy: the total matter and energy in the universe is always conserved.
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Can energy be changed Can energy be changed into matter?into matter?
• Think of matter and energy as two forms of the same thing that can be converted from one to another.
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E=mcE=mc22
• While it is possible to change matter into energy and energy into matter, the sum of the two is always constant.
• Einstein's equation shows this relationship. • E = Energy (Joules) • m = mass (kg) • c = speed of light (300,000 km/s)
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• The two most common energy conversions are:
• Potential energy changing into kinetic energy.
• Kinetic energy changing into potential energy
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• Mechanical energy= potential energy + kinetic energy
• Mechanical is energy due to the motion of an object
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Mechanical energyMechanical energy
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Forms of energyForms of energy• Mechanical• Chemical• Heat• Electromagnetic• nuclear
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Mechanical energyMechanical energy• There are two main types of mechanical
energy. • Motion energy: This is the energy
something has because it is moving • Stored mechanical energy: This is energy
something has stored in it because of its height above the ground or because it is stretched or bent or squeezed
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Electrical energyElectrical energy• The energy that flows through wires
and powers the lights and appliances in your home.
• The energy is in the form of moving electrons
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Electromagnetic energyElectromagnetic energy• Visible light or radiant energy• X rays• Radio waves• Microwaves• This form of energy can travel
through a vacuum
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• Concept Understanding: • • 1. Assume that all the matter in your body could be
converted into energy, how many Joules of energy would that be?
• Hint: 1 pound = 0.5 kg • Show all your work used to solve this problem.• 2. Give one example of each of the following energy
conversions: • Chemical energy changing into heat energy. • Heat energy changing into mechanical energy. • Nuclear energy changing into heat energy. • Mechanical energy changing into electromagnetic energy.
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Conservation Conservation • Matter can be changed into energy• Energy can be changed into matter• Neither can be created or destroyed
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WorkWork• Develop a definition from the activity
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WorkWork• W=force x distance• W=fxd• The unit is the newton/meter also
called joule• Work is force exerted through a
distance• Complete activity pg 303
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Measure workMeasure work• To measure work you must measure
the force in the direction of motion• Complete problems #3, 7, and 8 on
page 303
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PowerPower• Power=work/time• It is a rate• The unit is the watt---W or 1 j/s
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Analysis and conclusionAnalysis and conclusion• 1 When the mass is released from
the same height with the interrupter, is the ending height the same as its starting height? Use your data to support
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• 2 Analyze the energy transfers. At what point along a single swing does the mass have the greatest kinetic energy? The greatest potential energy
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• 3 Do the results support your hypothesis?
• 4 Compare the starting heights to the ending heights of the mass. Is there a pattern? Can you account for the observed behavior?
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• 5 Do your results support the law of conservation of energy? Why or why not?
• 6 What would happen if the mass of the bob was increased?