Post on 12-Jul-2015
transcript
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
3
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.
5
A formula to
find the
kinetic energy
of any body
based on its
velocity.
Calculating Kinetic Energy
6
Potential Energy•An object An object can store can store energy as energy as the result the result of its of its position.position.
7
Forms of potential energy
-position above the Earth’s surface
-stored in something stretchy
-chemical reaction
8
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
9
Elastic Potential
• Elastic PE is the energy stored in elastic materials as the result of their stretching or compressing.
11
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)
13
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
15
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
18
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.
19
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
•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.)
24
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.
25
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.