Transcript Conservation of Energy Notes

Conservation of Energy
Conservation of Energy
• We stated earlier that when one
object does work on another it
changes the motion (kinetic
energy) of the second object.
• This relationship between work
and kinetic energy is known as
the Work-Kinetic Energy
Theorem and can be expressed
as:
•
W net = ΔE
TME = Mechanical Energy (in the form
of potential energy)
Conservation of Energy
• In order to solve problems you
will be given appropriate
information to solve for either
work or both initial and final
kinetic energy. You can then
use the theorem to solve for
other quantities.
Conservation of Energy
• In the absence of friction or external
work, mechanical energy is
conserved, although it may be
converted from one type to another.
• KEi (initial kinetic energy)+GPEi
(intial gravitational potential
energy)+EPEi (initial elastic potential
energy)= KEf + GPEf + EPEf
• Let’s look at an animation that
shows this idea:
•
http://www.physicsclassroom.com/mmedia/energy/ce.html
Conservation of Energy
• This law, unlike the motion
equations already studied, can
be used to solve problems when
the acceleration is not
constant.
• Let’s do a practice problem (5D)
on pg. 181
Conservation of Energy
• When friction is involved, some of
our mechanical energy can be
converted into invisible forms of
non-mechanical energy. Mechanical
energy is no longer conserved, but
TOTAL ENERGY IS ALWAYS
CONSERVED
• Let’s do a practice problem on pg.
185
Power
• When work is put into an object,
energy is transferred from one
system to another.
• The rate that this happens is
described as Power
• P = W / time
• The units for power are
Joules/second, which are known
as Watts (W)
(don’t get confused between W=watts and W=work—one
is a unit and the other a symbol)
Power
• Another way to define power is force
multiplied by velocity
• P = (F)(v)
• The units work out the same:
• (Newton) x (meters/seconds) is the
same as (Newton x meter) / (s)
• We’ll do a practice problem on page
188.