Download Conservation of Energy

Conservation of Energy
BIOE201-B
The Law of Conservation of Energy
• Energy cannot be created or destroyed; it may
be transformed from one form into another,
but the total amount of energy never
changes.
What is energy?
• “the ability to do work”
• The combination of energy and matter make
up the universe:
– Matter is substance, and energy is the mover of
substance.
A Simple Example
This boiling tea kettle represents energy in motion. The water in the kettle is turning to
water vapor because heat is being transferred from the stove to the kettle. As the
entire system gets hotter, work is done—from the evaporation of the water to the
whistling of the kettle. (credit: Gina Hamilton)
Six fundamental forms of energy
1.
2.
3.
4.
5.
6.
mechanical energy
thermal (heat) energy
electromagnetic energy
electrical energy
nuclear energy
chemical energy
First Law of Thermodynamics
The first law of thermodynamics states that the change in internal energy of
a system equals the net heat transfer into the system minus the net work
done by the system. In equation form, the first law of thermodynamics is
ΔU=Q−W.
•
•
•
Heat and work are the methods of transferring energy for a system in thermal equilibrium
Q represents the net heat transfer—it is the sum of all heat transfers into and out of the system. Q is positive for
net heat transfer into the system.
W is the total work done on and by the system. W is positive when more work is done by the system than on it.
Making the Link:
The First Law of Thermodynamics and Law of
Conservation of Energy
The first law gives the relationship between heat transfer,
work done, and the change in internal energy of a system.
Heat transfer (Q) and doing work (W)
• The processes are quite different.
• Heat transfer, a less organized process, is driven by
temperature differences.
• Work, a quite organized process, involves a
macroscopic force exerted through a distance.
• Heat and work can produce identical results.
Heat transfer (Q) and doing work (W)
Both can cause a temperature increase.
Heat transfer and work are both energy in
transit—neither is stored as such in a system.
However, both can change the internal energy U of
a system.
Internal energy is a form of energy completely
different from either heat or work.
Energy is nature’s way of keeping score
• We sense energy only when the score changes
• either a transformation from one form of energy
to another
• or a transfer of energy from one point to another
How is all energy divided?
All Energy
Potential
Energy
Gravitation
Potential
Energy
Elastic
Potential
Energy
Internal
Energy
Kinetic
Energy
Chemical
Potential
Energy
Electromagnetic
Potential
Energy
Other Form of Energy (OE)
When does OE play a role? One example occurs when
a person eats.
Food is oxidized with the release of carbon dioxide,
water, and energy.
Some of this chemical energy is converted to kinetic
energy when the person moves.
Some of this chemical energy is converted to
potential energy when the person changes altitude,
and to thermal energy (another form of OE).
Energy of Various Objects and Phenomena
Object/phenomenon
Energy in joules
68
Big Bang
10
Energy released in a supernova
10
Annual world energy use
44
20
4×10
14
1 kg hydrogen (fusion to helium)
6.4×10
1 kg uranium (nuclear fission)
8.0×10
Hiroshima-size fission bomb (10 kiloton)
4.2×10
90,000-ton aircraft carrier at 30 knots
1.1×10
1 barrel crude oil
5.9×10
1 ton TNT
4.2×10
1 gallon of gasoline
1.2×10
Daily home electricity use (developed countries)
13
13
10
9
9
8
7
7×10
7
Daily adult food intake (recommended)
1.2×10
1000-kg car at 90 km/h
3.1×10
1 g fat (9.3 kcal)
3.9×10
ATP hydrolysis reaction
3.2×10
1 g carbohydrate (4.1 kcal)
1.7×10
1 g protein (4.1 kcal)
1.7×10
Tennis ball at 100 km/h
5
4
4
4
4
22
−6
Mosquito (10–2g at 0.5 m/s)
1.3×10
Single electron in a TV tube beam
4.0×10
Energy to break one DNA strand
10
http://cnx.org/contents/c5adb012-fbab-41a7-b5b2-4644984097fc@5#import-auto-id2866785
−15
−19
Potential
• energy of position or
energy in storage
• Water behind a dam
• Hammer over head
• Food on the plate
Kinetic
• energy of motion, form
capable of doing work
• Flowing water
• A falling hammer
• Electrons regenerating ATP
in a biological cell
PE = mgh
• m = mass (kg)
• h = height (m)
• g = accelaration
due to gravity
– (9.8 m/s2)
www.rigastagweekend.com
Gravitational Potential Energy (Ep)?
o Potential energy due to
an object’s position
o P.E. = mass x height x
gravity
What is Potential Energy?
o Energy that is stored
and waiting to be
used later
What is Elastic Potential Energy?
o Potential energy due to compression or
expansion of an elastic object.
What is Chemical Potential Energy?
o Potential energy
stored within the
chemical bonds of an
object
Kinetic Energy (Ek)
o Energy an object has due to
its motion
o K.E. = 1/2(mass x speed2)
KE = 1/2 m v2
•
•
•
•
4 kg bowling ball
at 10 m/s
= 0.5 (4kg) (10m/s)2
= 200 J
•
•
•
•
0.25 kg baseball
at 50 m/s
= 0.5 (.25kg) (50 m/s)2
= 312 J
Energy changes in a mechanical oscillator
Pendulum Motion
Work
The baseball pitcher put kinetic energy into the ball, so he did
work on it. To do the greatest possible amount of work, he
applied the greatest possible force over the greatest possible
distance.
Work is done when a force is exerted over a distance
Work
• is equal to the force that is exerted times the
distance over which it is exerted.
• W=Fxd
• The unit of work combines the unit of force
(N) with the unit of distance (m)
• Newton-meter (N-m) aka Joule.
You carry a 20 kg suitcase upstairs, a distance of
4m. How much work did you do?
•
•
•
•
•
•
W=Fxd
F = ma
= (20 kg) (10m/s2) = 200 N
W=Fxd
= (200 N) (4m)
= 800 J
Power
• measures the rate of work done.
• or the rate at which energy is expended.
• Power is the amount of work done, divided by
the time it takes to do it.
• Power (watts) = work (joules) / time (sec)
• P = W/t
Power
• Since work performed equals energy
expended,
• Power (watts) = energy (joules) / time (sec)
• The watt is defined as the expenditure of
1 joule of energy in 1 second.
(75 watt light bulb consumes 75 J/sec)
Important formulas and units
Quantity
Force
Work
Energy
Power
Definition
mass x accel.
force x distance
power x time
work / time
Units
newtons
joules
joules
watts
Ex. Problem on Power:
• Your CD system, uses 250 watts of electrical
power.
• You play it for 3 hrs. How much energy used?
About how much would it cost? If one kWh is
$.08.
• Energy (J) = power (watts) x time (sec) =
(250w) (3hr) = 750 Whr = .75 kWh
• The cost = 8 cents/ kWh x .75 kWh
• = 6 cents
Power = work / time
• Two physics students, Will N. Andable and
Ben Pumpiniron, are in the weightlifting room.
Will lifts the 100-pound barbell over his head
10 times in one minute; Ben lifts the 100pound barbell over his head 10 times in 10
seconds. Which student does the most work?
Which student delivers the most power?
Drawing Conclusions
•
•
•
•
•
Two divers of equal mass about to dive
Diver A has > Potential Energy than B
Compare divers positions
Which diver will hit water @ highest speed
What happens to energy when diver enters
the water?
What is the source of our energy?
• The source of
practically all our
energy is the Sun.
What is Mechanical Energy?
o Energy due to a object’s
motion (kinetic) or
position (potential).
• The bowling ball has
mechanical energy.
• When the ball strikes the
pins, mechanical energy
is transferred to the
pins!
Examples of Mechanical Energy
What is Electromagnetic
Energy?
o Light energy
o Includes energy from
gamma rays, xrays,
ultraviolet rays, visible
light, infrared rays,
microwave and radio
bands
What is Electrical Energy?
o Energy caused by
the movement of
electrons
o Easily transported
through power lines
and converted into
other forms of energy
What is Chemical Energy?
o Energy that is available for
release from chemical
reactions.
The chemical bonds in a
matchstick store energy that
is transformed into thermal
energy when the match is
struck.
Examples of Chemical Energy
What is Thermal Energy?
o Heat energy
o The heat energy of an object
determines how active its atoms are.
A hot object is one whose atoms and
molecules are excited and show
rapid movement.
A cooler object's molecules and atoms
will show less movement.
What type of energy cooks
food in a microwave
oven?
ELECTROMAGNETIC
ENERGY
What type of energy is the
spinning plate inside of a
microwave oven?
MECHANICAL ENERGY
Electrical energy is transported
to your house through power
lines.
When you plug an electric fan to
a power outlet, electrical
energy is transform into what
type of energy?
MECHANICAL ENERGY
What energy transformation
occurs when an electric lamp is
turned on?
ELECTRICAL ENERGY

ELECTROMAGNETIC ENERGY
The golfer in the photo is taking a swing. The
golf club starts at Point A and ends at Point E.
• Inferring At which point(s) does the golf club have the greatest potential energy? At
which point(s) does it have the greatest kinetic energy?
• Interpreting Diagrams Describe the energy transformations from Point A to Point E.
• Drawing Conclusions The kinetic energy of the club at Point C is more than the
potential energy of the club at Point B. Does this mean that the law of conservation
of energy is violated? Why or why not?
http://mycampus.nationalhighschool.com/doc/sc/Physical%20Science/iText/products/0-13-190327-6/ch13/ch13_ra_0.html
What types of energy are shown below?
Mechanical and Thermal Energy
(Don’t forget friction)
What type of energy is shown below?
Chemical Energy
What types of energy are shown below?
Electrical, Mechanical and
Electromagnetic Energy
What type of energy is shown below?
Chemical Energy (yummy)
What type of energy is shown below?
Thermal Energy
What types of energy are shown below?
Mechanical, Electromagnetic, Electrical, Chemical and
Thermal Energy
The Law of Conservation of Energy
• Energy cannot be created or destroyed; it may
be transformed from one form into another,
but the total amount of energy never
changes.
Bioenergetics
Ultimately, most life
forms get their energy
from the sun. Plants
use photosynthesis to
capture sunlight, and
herbivores eat the
plants
to
obtain
energy. Carnivores eat
the herbivores, and
eventual
decomposition
of
plant and animal
material contributes
to the nutrient pool.
http://cnx.org/contents/acdec277-bfc3-4144-8daa-c8d4264b5bd2@1
Bioenergetics is the concept of energy flow through living
systems, such as cells.
Cellular processes such as the building and breaking down of
complex molecules occur through stepwise chemical
reactions.
Some of these chemical reactions are spontaneous and
release energy, whereas others require energy to proceed.
http://cnx.org/contents/acdec277-bfc3-4144-8daa-c8d4264b5bd2@1