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Conservation of Energy

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Law of Conservation

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Properties of Energy• Energy is always “conserved”; it cannot be created or destroyed. • It can be transferred between objects or systems, from one form to another. • Changing energy back and forth from one form or state to another is how

we control it for our use.• Kinetic energy (KE) can be transformed into potential energy (PE) or from PE

to KE and still conserve the total energy of the system.

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Law of Conservation

• The law of conservation of energy states that energy is neither created nor destroyed in an ordinary chemical or physical process. • This is also known as the 1st Law of Thermodynamics.

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Potential and Kinetic Energy

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Energy

• In physics, energy is the ability to do work. • Work means a transfer of energy from one system to another that causes a

change in temperature, speed, position, pressure, or form of matter and that is a direct result of energy applied within a system (a set of things or parts that are related). • Therefore, energy is the capacity to use force to move an object over a

distance or to cause change in matter. • Energy is a quantity that can be measured.

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Energy

• The joule is the unit used to measure energy and is represented by J. • Joule units measure energy just like meters measure distance, degrees

measure temperature, or seconds measure time. • Joule units can be understood as how much energy is needed for change

within a system. • Energy that is stored, or able to do work but not currently doing work, is

called potential energy. • Energy in motion is kinetic energy.

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Energy

• All types of energy can be categorized as one of these two basic types of energy: kinetic energy and potential energy. • Potential energy and kinetic energy make up the total energy of a system.

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Chemical Potential Energy

• Sometimes potential energy is described as chemical potential energy because the energy is stored within the matter itself. • The chemicals that make up food and fuel all contain potential energy. • When you eat food, your body converts the energy in the foods from

potential energy into kinetic energy, which you can use to move and function. • When fuel is burned in a car engine, the fuel’s potential energy is converted

to kinetic energy that moves the car.

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Elastic Potential Energy

• Sometimes potential energy is described as elastic potential energy because it is stored in a stretched or compressed object such as a stretched slingshot or a compressed spring.

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Gravitational Potential Energy

• Objects have the potential to change their position due to the force of gravity pulling them down from a certain height. • A child at the top of a slide’s ladder has gravitational potential energy due

to the force of gravity pulling their body towards Earth’s surface. • This type of potential energy depends on the height above the surface and

the mass of the object. • The higher an object is and the more mass it has, the more potential energy

the object will have.

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Nuclear Potential Energy

• The energy stored in the nucleus of an atom is enormous. • Nuclear power plants used a controlled release of this energy in the

production of electrical energy. • Very small amounts are released in nuclear medicine applications such as

cancer treatment or special diagnostic procedures.

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Kinetic Energy

• Kinetic energy is the energy of motion. • Only matter in motion has kinetic energy. • Kinetic energy depends on an object’s mass and velocity. • The faster something is moving and/or the more massive it is, the more

kinetic energy it has.• Kinetic energy is motion of waves, electrons, atoms, molecules, substances,

and objects. • The motion can be large, such as in celestial bodies, moving organisms,

objects, machines, wind, waves, and sound; or small, such as in heated particles or the flow of charges.

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Radiant Energy

• The electromagnetic energy that moves as waves. • Radiant energy includes visible light, X-rays, gamma rays, and radio waves. • Sunshine is radiant energy, which is converted to the fuel and warmth that

make life on Earth possible.

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Thermal Energy

• Thermal energy is the vibration and movement of the atoms and molecules within substances. • As an object is heated up, its atoms and molecules move and collide faster. • Ovens, toasters, dryers, and heat lamps are examples of inventions that

convert electrical energy to thermal energy.

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Motion Energy

• Motion energy is the mechanical energy in the movement of objects. • It takes energy to get an object moving, and objects lose energy when they

slow down. • Wind and waves are an example of motion energy. • Energy is also defined as the work done by a force acting over a distance

and is measured in Newton-meters, called joules (J).

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Sound energy

• Sound energy is the movement of energy through substances in longitudinal waves. • Sound is produced when a force causes an object or substance to vibrate

and the energy is transferred through the substance in a wave.

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Electrical energy

• Electrical energy is delivered by the flow of tiny charged particles, typically moving through a wire. • Lightning is an example of electrical energy in nature so powerful that it is

not connected to a wire.

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Transforming Energy

• Energy has several properties. • For one, energy is always “conserved”; it cannot be created or destroyed. • It can, however, be transferred between objects or systems, from one form

to another. • Changing energy back and forth from one form or state to another is how

we control it for our use.

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Roller Coaster

• A roller coaster system is an example of transforming energy. • At the top of the hill, the roller coaster car has maximum PE (because the

car is at its highest point above the ground) and minimum KE (because the car is not moving). • As the car begins its journey down the slope, KE increases (because the car

is moving faster and faster) and PE decreases. • At the bottom of the slope, the car has minimum PE (gravity cannot pull

down any more) and maximum KE.

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Roller Coaster

• The car continues its journey upward, where it gains PE and loses KE. • At the top of the next crest, the cycle of transforming PE to KE begins again.

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Pendulum System

• A pendulum system consists of a mass hanging from a long cord attached to a pivot point, such as a clock pendulum arm, swinging wrecking ball, or child on a playground swing.• Imagine a pendulum mass is held upward to one side with a gravitational

potential energy (GPE or PE) of 100 joules. • At that beginning elevated position, the pendulum system has the greatest

potential energy, while kinetic energy (KE) is 0 joules (the mass is not moving).• When the mass is released and begins to move faster, it gains KE and loses

PE.

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Pendulum System

• At the bottom of the swing, KE is maximum at 100 joules and PE is 0 joules (gravity cannot pull down any farther, so there is no more gravitational potential energy).• The pendulum continues to swing, and so does the cycle of energy

transformation, until air resistance and friction on the pivot point slow the system down to a stop.

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