15.2 energy conversion and conservation 15.2 key concepts can energy be converted from one form to...
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15.2 Energy Conversion and Conservation
15.2 Key Concepts
• Can energy be converted
from one form to another?
• What is the law of
conservation of energy?
• What energy conversion
takes place as an object
falls toward Earth?
15.2 Energy Conversion and Conservation
The movement of a meteor represents what type of energy?
Some of this kinetic energy is converted into heat and light, or _______________ and ___________________ energy
thermalradiant
kinetic
15.2 Energy Conversion and Conservation
Upon impact, much of the meteor's remaining kinetic energy went into _________________ the rear of this car in Peekskill, New York.
Energy can be converted from one form to another!
crushing
15.2 Energy Conversion and Conservation
The process of changing energy from one form to another is energy ________________.
Energy Conversion
The striking of a match is a good example.
• Muscles use _______________ energy to move the match.
• Friction between the match and the matchbox converts kinetic energy into _____________ energy.
conversion
chemical
thermal
15.2 Energy Conversion and Conservation
The thermal energy triggers a chemical reaction on the match tip, releasing some of the match’s ________ chemical energy
This stored chemical energy is converted into ______________ and __________________ energy in the flame
Energy Conversion
stored
thermalradiant
15.2 Energy Conversion and Conservation
Conservation of Energy
The law of conservation of energy states that energy ______________ be created or destroyed.
It can only change ____________
cannot
form
15.2 Energy Conversion and Conservation
For example, the work down by friction changes ______________ energy into ______________ energy
Rub your hands against each other for a few seconds…what do you feel?
Recall that friction within machinery ____________ efficiency
Conservation of Energy
kinetic thermal
Heat!
reduces
15.2 Energy Conversion and Conservation
Even these skaters are subject to friction…they are slowed down by friction with the _________ and the _______________ of the ice.
Conservation of Energy
air surface
15.2 Energy Conversion and Conservation
Energy Conversions
As an object falls, its _____________ _____________ energy is converted to the ____________ energy of motion. .
Gravitational potential energy
Kinetic energy
gravitational potential
kinetic
15.2 Energy Conversion and Conservation
One of the most common energy conversions is between potential energy and kinetic energy.
• Example: A coiled spring has
____________ potential energy
when it is compressed
• When the spring expands, it is converted into ______________ energy
Energy Conversions
elastic
kinetic
15.2 Energy Conversion and Conservation
Some gulls use energy conversion to obtain _______while dropping oysters onto rocks.
The kinetic energy causes the shell to __________ on collision with the rock.
Energy Conversions
food
crack
15.2 Energy Conversion and Conservation
A pendulum consists of a weight _____________ back and forth from a rope or a string
Pendulum clocks use pendulums to maintain ______________ time.
The time it takes for a pendulum to swing back and forth once is precisely related to its _________.
Energy Conversions
swinging
accurate
length
15.2 Energy Conversion and Conservation
Where does the pendulum have the greatest potential energy?
Where does the pendulum have the greatest kinetic energy?
Energy Conversions
Highest point of swing
Bottom of swing
15.2 Energy Conversion and Conservation
Energy Conversion and the Pole VaultIn the pole vault, an athlete uses a flexible pole to propel himself over a high bar.
As the pole bends, some
of the kinetic energy
is converted into
____________
____________ energy
Energy Conversions
elastic
potential
15.2 Energy Conversion and Conservation
The pole springs back into shape, propelling the pole-vaulter _______________.
• As the pole-vaulter rises, his kinetic energy ______________ while he _________ gravitational potential energy.
• What type of energy
does the pole-vaulter
have at his highest point?
Energy Conversions
upward
decreasesgains
Gravitational p. e.
15.2 Energy Conversion and Conservation
As he falls, what type of energy does he have?
Energy Conversions
Kinetic energy
15.2 Energy Conversion and Conservation
Energy Conversion Calculations
Recall that mechanical energy is the __________ kinetic and potential energy of an object
Mechanical energy = KE + PE
When friction is small enough to be ___________, and ______ mechanical energy is added to a system, then the system’s mechanical energy does ______ change.
Energy Conversions
total
ignoredno
NOT
15.2 Energy Conversion and Conservation
The law of conservation of energy applies to any mechanical process.
If friction can be neglected, the total mechanical energy remains _______________.
Energy Conversions
constant
15.2 Energy Conversion and Conservation
Conservation of Mechanical EnergyAt a construction site, a 1.50-kg brick is dropped from rest and hits the ground at a speed of 26.0 m/s. Assuming air resistance can be ignored, calculate the gravitational potential energy of the brick before it was dropped.
Mass =
Speed =
Is the brick initially moving?
Energy Conversions
=
1.50 kg
26.0 m/s
noPE = 1/2 (1.50 kg) (26.0 m/s)2
= 507 J
15.2 Energy Conversion and Conservation
A pendulum with a 1.0-kg weight is set in motion from a position 0.04 m above the lowest point on the path of the weight. What is the kinetic energy of the pendulum at the lowest point? (Hint: Assume there is no friction.)
Mass =
Height =
Energy Conversions
(PE)beginning = mgh = (KE)
1.0 kg
0.04 m
(1.0 kg)(9.8 m/s2)(0.04m) = KE
0.4 J = KE
15.2 Energy Conversion and Conservation
Energy and Mass
Einstein’s equation,
E = mc2, says that energy and mass are ________________ and can be ____________ into each other.
equivalentconverted
15.2 Energy Conversion and Conservation
Albert Einstein developed his special theory of __________________ in 1905. This theory included the now-famous equation E = mc2.
• E is _______________• m is _____________ • c is the ________________________ = 3.0 × 108 m/s
A __________ amount of matter can produce
an _____________ amount of energy.
Energy and Mass
relativity
energy
mass
speed of light
small
enormous
15.2 Energy Conversion and Conservation
Assessment Questions
1. What energy conversion occurs as a result of friction? (think of rubbing your hands)a. chemical energy to thermal energy
b. kinetic energy to potential energy
c. kinetic energy to thermal energy
d. potential energy to thermal energy
15.2 Energy Conversion and Conservation
Assessment Questions
2. At what point in a pendulum’s swing does it have maximum kinetic energy?a. the highest point of the swingb. the lowest point of the swingc. halfway between the lowest and highest pointd. same at all positions of the swing