Lesson: Energy Flow
Field Museum Extensions
a. Related Exhibitions.
1. Native North Americans: Native Peoples of the Northern Woodlands. In
this exhibit and others described below, students will brainstorm to find
situations in which potential energy is transformed into kinetic energy.
Also, students will make a list of all measurable characteristics that could
be used in an equation to calculate the potential and/or kinetic energy.
They should focus on tools, weapons, or part of an exhibit where a change
is shown or described.
For example, when an arrow is drawn back by a bow, the tension in the
bowstring imparts a potential energy to the bow and arrow. This potential
energy is transformed into kinetic energy when the bowstring is released.
Measurable characteristics that could be used to calculate the potential
energy of the bow and arrow include the length of the bow, the tension in
the string, and the mass of the arrow. The kinetic energy would be
calculated using the mass of the arrow and its speed.
Tools used to grind grain are on display. The potential energy of the tool
being used is greatest when the grinding stone is held highest above the
dish. The transformation from potential energy to kinetic energy is
complete when the grinding stone is just touching the grain. In this
system, students should state that the energy transfer is not as simple as
the energy transfer of a free-falling object. The grinding stone is not
dropped but is moved in a controlled fashion over the grain. Therefore,
the height of the stone and its mass cannot be used in a simple equation
such as PE = mgh. Although mass, m, and height, h, would be variables
to consider to calculate the potential energy, PE, a complex equation that
includes the tension change in the operator’s arm would replace the
gravitational acceleration constant, g.
Some students may list a cooking fire shown in one of the exhibit’s
dioramas as a situation where there is an energy transformation. Potential
energy is the ability to change or cause change because of position or
composition. So, the composition of the wood is a form of chemical
potential energy that will be transferred to the kinetic energy of the gas
molecules in the fire as well as the food and water particles in the cooking
pot. (Temperature is related to the average kinetic energy of particles of
matter, so whenever there is an increase in temperature, there is an
increase in molecular kinetic energy.) An equation to calculate the kinetic
energy increase would incorporate the temperature change, the mass of the
material, and some factor related to the identity of the material.
2. Rocks and Minerals Exhibit—Weathering and Erosion. In this display,
students can identify many changes in which there is a potential energy to
kinetic energy transformation.
For example, frost action that breaks down rock is an energy change. As
water freezes in a confined space it starts to expand. As a result, huge
stresses build in the rock and ice. This creates a high potential energy
system. The energy change occurs when the stress is released as the rock
breaks. The forces that build up and the distance the rock pieces are
separated can be used to calculate an energy change called work (W =
Force x distance). The work is both a potential energy decrease and a
kinetic energy increase. Students may need to be reminded that if a
kinetic energy increase cannot be easily calculated and therefore remains
unknown, but a potential energy decrease can be readily calculated using
measurable quantities, then the law of conservation of energy can be
applied to determine the unknown. In the case above, neither the potential
energy nor kinetic energy was calculated, but the energy transfer (called
work) could be calculated. Often times, this is the case with energy
conversions. For example, in the case of a temperature change, it is the
energy transfer called heat that is calculated.
Also in this exhibit are other examples of weathering. Students might
identify these as forms of kinetic energy to potential energy transfers. The
motion of wind or water breaks and separates particles. The “breaking”
on the molecular level is a potential energy increase as bonded atoms,
ions, and molecules are pulled apart. Until the bonds break, the potential
energy increase is similar to the increase when a rubber band is stretched.
Eventually, the bonds break and particles move, just like a rubber band
snapping and moving.
3. Rocks and Minerals Exhibit—The Moving Earth. This exhibit shows
tectonic plate movement during earth’s history. Over time, the continents
have risen above and below sea level and have moved closer and farther
away from each other. Students will study the movie and the model of the
earth and its interior to try to identify energy changes.
For example, students might identify the hot magma below the earth’s
crust as a high potential energy system. The magma, because of its
temperature, is buoyant. Until the magma starts to move, all of its ability
to change is potential. The potential energy would be calculated using the
mass and volume of the magma (a function of its temperature), as well as
the density of the surroundings (also a function of temperature). As the
magma rises, its kinetic energy is a function of its mass and speed. When
the magma spreads out along the underside of the crustal plate, frictional
forces cause the plate to move. Students might notice that the energy
transfer from potential energy to kinetic energy is not complete. Some
energy change is involved in changing temperatures. Also, the concept of
entropy and the scientific law that no energy transfer is 100% efficient
could be a part of the description of this exhibit.
The three exhibits above are only a starting point for discussion of energy
transfers. All changes involve energy transfers and every exhibit in the
museum involves some types of change. Teachers should pick the
exhibits that most interest them and their classes to discuss energy
changes. Much of the same science described above would apply in those
situations.
b. Harris Educational Loan Center.
1. Renewable and Nonrenewable Energy Experience Box. Energy resources
are simply high potential energy systems that can be harnessed to move
machines, create electricity, or warm materials. In each of the situations,
there is a potential energy to kinetic energy transformation. This
Experience Box shows examples of energy resources that students can
investigate for the type of energy transfer occurring.
For example, for fossil fuels, the potential energy of coal, petroleum, or
natural gas is transformed into the motion energy of air or water molecules
(the temperature of the air or water increases). The energy transfer is
called heat because it accompanies a temperature change. Usually, the
high temperature material is confined to a small volume, which results in a
pressure increase. The high-pressure gas is a high potential energy
system. The potential energy of the gas is transferred to the kinetic energy
of a turbine or a piston. When electricity is generated, the kinetic energy
of the turbine moves magnets past copper wire. In and around the wire, the
changes in the magnetic field create a high potential energy system. This
potential energy is then changed into the kinetic energy of moving
electrons in the wire. The moving electrons are electricity and this kinetic
energy may be harnessed to do a variety of tasks.
Students should investigate the differences between these energy changes
and those that occur during use of a renewable energy. For example,
instead of confining a hot gas inside of a boiler to turn the turbine, the high
pressure, and therefore, high potential energy, of wind can be used to turn
the blades of a turbine. Or instead of creating a hot gas by burning a fuel,
the infrared light from the sun can be magnified in a solar heater.
2. The Moving Earth Video and Interior of the Earth Exhibit Case. The
video is about plate movement over geologic time. This is the same video
that students will see in the Rocks and Minerals exhibit. Energy changes
can be analyzed by watching the video and by investigating the Interior of
the Earth Exhibit Case.
3. Eskimo Hunting and Fishing Experience Box. This Experience Box
includes tools such as spears and fishing gear used by Arctic Peoples.
Students can analyze these for energy changes. Students should be
reminded that every change (such as a spear being thrown) results from
some energy transfer. So each of these tools, because they operate on
some change, also incorporate a potential energy to kinetic energy change.
For example, the fishing gear is a high potential energy system when the
fishing rod is bent and the fishing line is taught. The potential energy is
transferred into the kinetic energy of the hook (and fish).
c. Field Museum Science/Website Resources.
1. Nature Unleashed Webpage
http://www.fieldmuseum.org/natureunleashed/
Natural disasters are dramatic examples of energy transfer. Students
should investigate the origins and effects of volcanoes, earthquakes,
tornadoes, and hurricanes to identify potential energy to kinetic energy
transformations.
For example, a tornado begins when two air masses with different
densities come into contact. The more buoyant air mass in the denser air
mass is a high potential energy system. As the buoyant air begins to rise,
potential energy is changed to kinetic energy. And as the rising air mass
leaves the ground, a low-pressure area is created. This is another high
potential energy system. Surrounding air is pushed into the low-pressure
area, so potential energy is again changed to kinetic energy. Then, the
process repeats. In the end, winds rushing toward the point of rising air,
combined with strong winds in the upper atmosphere spinning the rising
air mass, results in the tornado.