Transcript Conservation of Energy

I.P.C. 6 A
Describe the law of conservation
of energy. (This law includes
calculation of G.P.E.)
Conservation of Energy
Energy in a system may take on
various forms (e.g. kinetic,
potential, heat, light). The law of
conservation of energy states
that energy may neither be
created nor destroyed. Therefore
the sum of all the energies in the
system is a constant.
Example: A roller coaster on top
of a hill has potential energy.
When the roller coaster rolls
downward the PE is converted
into Kinetic Energy.
• The sun or solar energy
is the source of energy
for all living organisms.
• In photosynthesis,
plants convert solar
energy into stored
glucose (sugar) energy.
• This energy is
transferred to animals
through the food chain
APPLYING THE CONSERVATION
OF ENERGY
Mechanical
Energy
Heat
Energy
Electrical
Energy
(Energy can be converted from one form of energy to another,
but energy never just appears or disappears.)
Which of the following is an example of
solar energy being converted into
chemical energy?
TAKS 2004
A. Plants producing sugar during the day
B. Water evaporating and condensing in the
water cycle
C. The sun unevenly heating Earth’s surface
D. Lava erupting from volcanoes for many
days
Answer: A, because plants use sunlight to
make sugar which is a stored chemical
energy for them to use.
Why is the sum of the products’ energy in
this reaction less than the sum of the
reactant’s energy?
TAKS 2004
A. Energy is given off as heat
B. The products absorb available energy
Answer:
A, because
not lost or gained
C. Energy
is trappedenergy
in the is
reactants
but
converted
to other
forms.
Heat
D. can
Thebe
reactants’
energy
is less
than
the or
Thermal
Energy
common conversion.
melting
pointisofone
glucose
An inventor claims to have created an
internal combustion that converts 100kJ of
chemical energy from diesal fuel into
140kJ of mechanical energy. This claim
violates the law of conservation of:
TAKS 2004
A. momentum
B. inertia
Answer: C, because by changing 100kJ of
C.
energy
energy
into 140kJ you have created energy
D.
mass
which
violates the law of conservation of
energy.
Fuel cells powered by plankton from the
seabed can be used to operate instruments
that monitor ocean currents and water
temperature. These fuel cells get their
energy by converting –
A. chemical energy to electrical energy
B. electrical energy to mechanical energy
Answer:
A, because
plankton
(plants) convert
C.
hydroelectric
energy
to geothermal
energy
sunlight to glucose (chemical energy) which is
D. mechanical energy to chemical energy
converted to electrical energy to power fuel
cells.
YOUR TURN
GET OUT
SCRAP PAPER
AND YOUR
FORMULA
CHART
Formula Chart
Formulas
Today we will work
with the kinetic
energy and
gravitational
potential energy
formulas. Find them
on your Formula
Chart.
Constants,
Symbols and
Units
K.E. and
G.P.E.
KINETIC ENERGY
Kinetic energy is the energy of motion. An
object which has motion - whether it be
vertical or horizontal motion - has kinetic
energy. There are many forms of kinetic
energy - vibrational (the energy due to
vibrational motion), rotational (the energy
due to rotational motion), and translational
(the energy due to motion from one location
to another).
What is the kinetic energy of a 625-kg
roller coaster car that is moving with a
speed of 18.3 m/s.
K.E. = (625) x (18.3)2 = 104653.12 J
2
Answer: D 1.05 x 105 Joules
POTENTIAL ENERGY
Potential energy is energy that is
stored in an object. (A stretched
rubber band has potential energy.
When you release the stretch the
potential energy is converted to kinetic
energy and the rubber band flies
through the air. (Kinetic energy is
energy of motion) Notice the potential
energy was changed to kinetic energy
but no energy was lost or gained.
Gravitational potential energy is the
energy stored in an object as the result
of its vertical position or height.
(Example a boulder on top of a
mountain)
GRAVITY
Formula Chart
Formulas
In GPE problems we
need to know what
force gravity exerts.
Where do we get the
information?
Gravity =
9.8 m/s2
Constants, Symbols
and Units
What is the potential energy of the rock?
TAKS 2003
A.
B.
C.
D.
59,900 J
64,600 J
93,100 J
121,500 J
What is the potential energy of the rock?
A.
B.
C.
D.
59,900 J
64,600 J
93,100 J
121,500 J
P.E. = (95)(9.8)(100)
TAKS 2003
What is the approximate difference in
gravitational potential energy of the two
shaded boxes?
TAKS 2005-06
A.
B.
C.
D.
19 J
39 J
59 J
79 J
What is the approximate difference in
gravitational potential energy of the two
shaded boxes?
TAKS 2005-06
A.
B.
C.
D.
19 J
39 J
59 J
79 J
P.E. = (2)(9.8)(3.0) =58.8
58.8 – 19.6 = 39.2 J
P.E. = (2)(9.8)(1.0) =19.6
FOLDABLE TIME
Make a Foldable for Gravitational
Potential Energy and Kinetic
Energy