THE ABILITY TO CAUSE CHANGE

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mechanical energy

Types of Types of

EnergyEnergy

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types of energy

oThermal energy - due to

temperature (recall that this comes  from the motion of molecules, so it

is really kinetic energy)

oHeat energy -transfer of thermal

energy

oChemical Potential Energy - stored

in chemical bonds

oNuclear energy - stored in the

nuclei of an atom

oElectrical energy - EM interactions

oRadiant energy -carried by EM waves

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Energy• Energy is the capacity (ability) to do work. 

• Kinetic Energy: Associated with an object in motion

• Potential Energy: Present in an object that has the potential to move because of its position

4CLIP

Kinetic Energy• MotionMotion• KE of an object depends KE of an object depends

upon two variables: upon two variables:

1.1.the mass (m) of the the mass (m) of the objectobject

2.2.the speed (v) of the the speed (v) of the object.object.

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A formula to

find the

kinetic energy

of any body

based on its

velocity.

Calculating Kinetic Energy

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Potential Energy•An object An object can store can store energy as energy as the result the result of its of its position.position.

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Forms of potential energy

-position above the Earth’s surface

-stored in something stretchy

-chemical reaction

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Gravitational Potential Energy• GPE is the energy stored in

an object as the result of its vertical position (i.e., height).

• Amt. of GPE is dependent on two variables:1.the mass2.the height

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Calculating Gravitational

Potential Energy

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Elastic Potential

• Elastic PE is the energy stored in elastic materials as the result of their stretching or compressing.

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Conservation of

Energy

Conservation of Energy

Energy cannot be created or Energy cannot be created or

destroyed…only changed destroyed…only changed

from one form to another.from one form to another.

The total energy of an isolated

system remains constant

(isolated systems have no

external forces and no mass

changes)

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14 ENERGY BEFORE =

ENERGY AFTER

Energy can be changed from one form to

another, but it does not disappear.

Mechanical Energy• The motion of some objects contain a combination of only kinetic and potential energies.

• ME is the sum of the KE and forms PE associated with a system

• Therefore, ME= KE + PE

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TOTAL ENERGY OF THE SYSTEM REMAINS THE SAME

Conservation of Energy

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Conservation of EnergyConservation of Energy

TOTAL ENERGY OF THE SYSTEM REMAINS THE SAME

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Conservation of Mechanical Energy :

Therefore,

ME i = ME f

KE i + PE i = KE f + PE f

½ mv i2 + mgh i = ½ mv f

2 + mgh f

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Conservation of Mechanical EnergyConservation of Mechanical Energy ::

• Conservation of ME only hold true when the only energies of the system are KE and PE.

• Therefore, in the presence of friction energy is transformed to other types of energies.

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Energy Conversion

When one type of energy is changed or transformed into another type of energy

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Can you think of More?

Create a graphic organizer to illustrate energy

conversions. draw a picture to represent four

different energy conversion you may encounter in

everyday life. Be sure to explain what type of

energy it starts with and what type of energy it

ends with.

Examples21

Battery

Lighting a MatchStea

m Engine

Energy Conversion

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What about a falling object?

What happens when it hits the ground?

Where did the energy all go?

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•As it is falling and when the object hits the ground the energy is converted into other types of energy such as:

Energy Conversions of a dropped object

•If the object bounces, some energy is converted momentarily into elastic potential energy.

•sound energy (waves), Light Energy (sparks), thermal energy due to friction (heat) in the ground and air, vibrations in the earth (energy waves.)

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If Robin Hood had been Written by an Engineer....

    And Robin didst slowly and with great determination put potential energy equal to the work of his muscles into an elastic storage device.                                                                               

And therewith Robin the Bold and Valiant didst convert this stored energy most quickly, efficiently, and accurately into the velocity of a sturdy and pointed dart (oft called arrow) such that almost all of its former potential energy didst become kinetic. Then this speedy dart didst split an arrow (oft called dart) already buried in most distant 

target, having been previously hurled there at an equally great speed by a similar conversion of stored energy. 

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EOCT QuestionsEOCT Questions

Which statement about energy is true?A Energy can be increased in a closed system.B Energy cannot be conserved.C Energy can be decreased in a closed system.D Energy cannot be created nor destroyed.