Transcript Energy and Systems Unit 3 Energy and Systems Chapter 8 Energy Flow and Systems  8.1 Energy Flow  8.2 Power, Efficiency and Thermodynamics  8.3 Systems.

Energy and Systems
Unit 3 Energy and Systems
Chapter 8 Energy Flow and Systems
 8.1
Energy Flow
 8.2
Power, Efficiency and Thermodynamics
 8.3
Systems in Technology and Nature
8.1 Investigation: Energy Flow in a System
Key Question:
How does energy move
through a series of
transformations?
Objectives:
Create an energy flow diagram to document the energy
transformations that occur as the Energy Car moves along
the SmartTrack.
 Discuss the factors which affect the efficiency of a system.
 Suggest and test modifications to improve the efficiency of a
system.

Energy Flow
 Our
universe is matter and
energy organized into
systems.
 There
Earth is a system.
are systems within
systems ranging in scale
from the solar system, to
Earth, to a single animal, to
a single cell in the animal,
right down to the scale of a
single atom.
Energy and change
 The
energy available to a
system determines how much
the system can change.
 By
looking at how much
energy there is in a system,
and how much energy is used
by the system, you can tell a
lot about what kinds of
changes are possible.
How fast will the green ball travel
if the only source of energy is the
falling blue ball?
Different forms of energy
 Mechanical
energy is the energy possessed by
an object due to its motion or its position.
 Radiant energy includes light, microwaves, radio
waves, x-rays, and other forms of electromagnetic
waves.
 The electrical energy we use is derived from
other sources of energy.
 Chemical energy is energy stored in the bonds
that join atoms.
 Nuclear energy is released when heavy atoms in
matter are split up or light atoms are put together.
The workings of the universe can be
viewed as energy flowing from one
place to another and changing back
and forth from one form to another.
Potential energy

Systems or objects with potential energy are able
to exert forces (exchange energy) as they change.

Potential energy is energy due to position.
Kinetic energy

Energy of motion is called kinetic energy.

A moving cart has kinetic energy because it can hit
another object (like clay) and cause change.
Energy in a closed system
 The
conservation of
energy is most useful
when it is applied to a
closed system.
 Because
of the
conservation of energy,
the total amount of matter
and energy in your system
stays the same forever.
Energy flow diagrams
 An
energy flow
diagram is a good
way to show what
happens to the
energy in a system
that is changing.
 Each
place where
energy changes
form is called a
conversion.
Unit 3: Energy and Systems
Chapter 8: Energy Flow and Systems
 8.1
Energy Flow
 8.2
Power, Efficiency and Thermodynamics
 8.3
Systems in Technology and Nature
8.2 Investigation: People Power
Key Question:
What’s your work and power as
you climb a flight of stairs?
Objectives:
Identify the factors that determine the work a person does
and his or her power output.
 Calculate work and power.
 Relate the work done in joules to the Calories used in the
process.

Power, Efficiency, and Thermodynamics
 In
order to raise a 1,000kilogram car 1 meter, you
need 9,800 joules of energy
 Doing
the lift in 10 seconds
requires a power output of
980 watts.
 This
is more than a human
can do.
Power
 Power
is the rate of converting energy, or doing
work.
 How
fast you do work makes a difference
Power in flowing energy
 Power
is used to describe these three similar
situations. In each, you calculate the power by
dividing the energy or work by the time it takes for
the energy to change or the work to be done.
1. Work is done by a force. Power is the rate at which
the work is done.
2. Energy flows from one place to another; power is
the rate of energy flow.
3. Energy is converted from one form to another.
Power is the rate at which energy is converted.
An example
 The
Colorado River
flows at 700 m3/s.
 Hoover
Dam converts
the potential energy of
the Colorado River into
electricity
Calculating power in a system
A 2-kg owl gains 30 m of height in 10 s.
How much power does the owl use?
1.
Looking for: … power.
2.
Given: … owl’s mass (2 kg), height (30 m) and time (10 s).
3.
Relationships: Power = energy ÷ time and Ep = mgh
4.
Solution: Ep = (2 kg)(9.8 N/kg)(30 m) =588 joules
Power = 588 J ÷ 10 s = 58.8 watts
Efficiency
 The
efficiency of a process
describes how well energy
or power is converted from
one form into another.
 Efficiency
is the ratio of
useful output energy or
power divided by input
energy or power.
 If
you could add up the
efficiencies for every single
process in a system, that
total would be 100 %.
Calculating efficiency of a process
A 12 g paper airplane is launched at a speed of 6.5
m/s with a rubber band. The rubber band is
stretched with a force of 10 N for a distance of 15
cm. Calculate the efficiency of the process of
launching the plane.
1.
2.
3.
4.
Looking for: … efficiency.
Given: … plane’s mass (12 kg), and speed (6.5 m/s) and
the rubber band’s force (10N) and distance (.15 m)
Relationships: Efficiency = Eo ÷ Ei Input energy is work =
F × d; and Output energy: Eo = (½) mv2
Solution: e = [(0.5)(0.012 kg)(6.5 m/s)2] ÷ [(10 N)(0.15 m)]
= 0.17 or 17%
Energy in the U.S.
 In
the United States, about
89% of the energy sources
used to generate electricity
power are fossil fuels—coal,
gas, oil—or nuclear energy.
Thermodynamics
 Thermodynamics
is the physics and study of heat.
 The
law of conservation of energy is also called the
first law of thermodynamics.
 It
states that energy cannot be created or destroyed,
only converted from one form into another.
 The
second law of thermodynamics states that
when work is done by heat flowing, the output work
is always less than the amount of heat that flows.
Efficiency of an engine
 Entropy
is a measure of
the energy in a system
that is “lost” as waste
heat and that cannot be
used to do work.
 Entropy
helps explain
why processes that are
not 100 percent efficient
are irreversible and why
time only moves forward.
For example, 64% of the
energy in gasoline flows out
the car’s tailpipe, radiator, and
other parts as waste heat!
Efficiency in biological systems
 In terms of output work, the
energy efficiency of living
things is typically very low.
 Almost all of the energy in
the food you eat becomes
heat and waste products;
very little becomes physical
work.
Estimating efficiency of a human
 To
estimate the efficiency of a
person doing physical work,
consider climbing a mountain
1,000 meters high.
 A human
body doing
strenuous exercise uses about
660 kilocalories per hour.
The overall energy
efficiency for a person is
less than 8%.
 If
it takes three hours to climb
the mountain, the body uses
1,980 Kcal (8,300,000 J).
Unit 3: Energy and Systems
Chapter 8: Energy Flow and Systems
 8.1
Energy Flow
 8.2
Power, Efficiency and Thermodynamics
 8.3
Systems in Technology and Nature
8.3 Investigation: Transportation Efficiency
Key Question:
Which transportation method
is the most efficient?
Objectives:
Discuss the factors that influence the efficiency of
transportation methods.
 Use the Internet to research the fuel consumption of different
types of vehicles.
 Compare the energy requirements for different methods of
vehicle and human-powered transportation.

Energy flow
 The
energy flow diagram
for a rechargeable
electric drill shows losses
to heat or friction at each
step.
Power in human technology
 You
probably use machines with a wide range of
power every day.
 Machines
are designed to use the appropriate
amount of power to create enough force to do
work they are designed to do.
Estimating power requirements

You can calculate the power
required if you know the force you
need and the rate at which things
have to move.

Suppose your job is to choose a
motor for an elevator.

The elevator must lift 10 people,
each with a mass of 70 kg.
Estimating power requirements
 The
 The
smallest motor that would do the job is 19.6 hp.
actual motor required would be about three
times larger (60 hp) because our calculation did not
include any friction and assumed an efficiency of
100 %.
Energy flow in
natural
systems
 Steady
state means there is a
balance between energy in and
energy out so that the total
energy remains the same.
 On
Earth, radiant energy from
the Sun is energy input.
 The
average energy of the
Earth stays about the same
because energy input is
balanced by its energy output,
energy that is radiated back
into space.
Energy flow in natural systems
 The
energy flows in
technology tend to start
and stop.
 Many
of the energy flows
in nature occur in cycles.
 Water
is a good example.
Power in natural systems
 The
power received from the
Sun drives the weather on
Earth.
 A 10
m/s wind gust represents
only 4% of the available solar
power on a 1 km2 area.
Energy flow in natural systems
 A food
chain is a series of processes through
which energy and nutrients are transferred
between living things.
 A food
 A food
chain is like one strand in a food web.
web connects all the producers and
consumers of energy in an ecosystem.
Energy flow in natural systems
 The
energy pyramid
is a good way to show
how energy moves
through an ecosystem.
 Energy
flows from
producers to
consumers.
Energy from Ocean Tides

The energy and power in tides is enormous.

The power that moves the oceans and creates tides comes from
the total potential and kinetic energy of the Earth-Moon system.

Many experimental projects have been built to harness the
power of tides.

Like hydroelectric power, energy from tides creates no
pollution, nor does it use up fossil fuels such as petroleum or
coal.