Transcript The Concept of Energy

Topic 8: Energy & the Price
We Pay
Dr. George Lapennas
Department of Biology
What is Energy?
Short answer: Energy is the ability to do
Work.
What is Work?
Work is done when a Force acts through a Distance in the
direction of the Force
Work = Force x Distance
Are these guys doing Work?
Is this guy doing Work?
Now has this guy done
Work?
Power = Work / Time
= (Force x Distance)/Time
= Force x (Distance/Time)
= Force x Velocity
Power = Work / Time
1 “horsepower” =
550 foot-pounds/second
Power = Work / Time
1 “horsepower” =
550 foot-pounds/second
4 Fundamental forms of Energy:
1 Potential Energy (PE)
2 Kinetic Energy (KE)
3 Electro-Magnetic Energy (E-M)
4 Mass Energy
1 Potential Energy (PE) = “energy of position”
Energy gained by pulling something away from an
attractive force
or
Energy gained by pushing something toward a
repulsive force
1 Potential Energy (PE) = “energy of position”
Gravitational PE = work done to lift something against attraction of
gravity
Gravitational PE gained = weight x height lifted = mg x h
1 Potential Energy (PE) = “energy of position”
Elastic PE = stretching a spring or a rubber band or compressing a spring
or a gas or bending a springy bow
1 Potential Energy (PE) = “energy of position”
Electrical PE = pulling + away from –
pushing + toward + or – toward –
1 Potential Energy (PE) = “energy of position”
Electrical PE = pulling + away from –
pushing + toward + or – toward –
1 Potential Energy (PE) = “energy of position”
Magnetic PE
Chemical Potential Energy
Work done against Friction does not yield Potential Energy
4 Fundamental forms of Energy:
2 Kinetic Energy = “energy of motion”
3 Electro-Magnetic Energy = light, ultraviolet, x-rays, radio waves,
micro-waves
3 Electro-Magnetic Energy = light, ultraviolet, x-rays, radio waves,
micro-waves
3 Electro-Magnetic Energy = light, ultraviolet, x-rays, radio waves,
micro-waves
3 Electro-Magnetic Energy = light, ultraviolet, x-rays, radio waves,
micro-waves
4 Mass Energy = energy derived from mass
4 Mass Energy = energy derived from mass
4 Mass Energy = energy derived from mass
4 Mass Energy = energy derived from mass
Internal energy
First Law of Thermodynamics
“Conservation of Energy”
Energy can neither be created nor destroyed
The amount of Energy in an “isolated system” is
constant over time
An isolated system is one where neither matter nor energy can cross
between the system and the surroundings.
The whole universe itself is an isolated system, as there are no
surroundings to exchange matter or energy with.
An isolated system is one where neither matter nor energy can cross
between the system and the surroundings.
The whole universe itself is an isolated system, as there are no
surroundings to exchange matter or energy with.
Energy can be transferred (moved) from one place to another
and
Transformed from one form to another
Internal energy
A closed system is one where
energy can cross the boundary,
but matter cannot.
The internal energy of a closed system
changes with heat transfer and work
done
Energy transformation from one form
to another
Energy transformation from one form
to another
Pile driver
Energy transformation from one form
to another
Pile driver
Energy transformation from one form
to another
Pile driver
Energy transformation from one form
to another
Pile driver
Energy transformation from one form
to another
Pile driver
Energy transformation from one form
to another
Energy transformation from one form
to another
Energy transformation from one form
to another
Energy transformation from one form
to another
Energy transformation from one form
to another
Energy transformation from one form
to another
Energy transformation from one form
to another
Second Law of Thermodynamics
The Entropy of the Universe can only increase (or stay the same) over
time.
It cannot ever decrease.
Entropy = disorder = randomness
Second Law of Thermodynamics
The Entropy of the Universe can only increase (or stay the same) over
time.
It cannot ever decrease.
Entropy = disorder = randomness
All “changes” that can actually occur result in an increase in the
Entropy of the Universe
Entropy is “Time’s Arrow” which points in the direction of “spontaneous”
changes = changes that can happen
Entropy is “Times Arrow”
Entropy is “Times Arrow”
Second Law of Thermodynamics - Examples
Temperature- a measure of the
average kinetic energy of the
molecules making up a
substance.
Heat- energy of molecules that is
gained/lost through a temperature
difference.
Second Law of Thermodynamics - Examples
Second Law of Thermodynamics - Examples
PE-KE-Elastic E-KE-PE-KE- Elastic E-KE-PE-Elastic E …
Entropy
Every actual change results in some energy
becoming unavailable for doing work
There are no perfect heat engines
There are no perfect heat engines
The End