Patricia Higby
Energy Education and Outreach Coordinator
University of Northern Iowa
[email protected]
(319) 273-6012
Why we need to change the way we teach the Conservation of Energy Law
Keywords: Conservation of Energy, Matter, Einstein
Abstract
How do you teach the Law of Conservation of Energy? Is it “Energy cannot be created or
destroyed, just transformed from one form to another”? Are those forms kinetic and potential
energy, including the classic nine of chemical, nuclear, stored mechanical, gravitational, radiant,
thermal, motion, sound, and electrical energy? Do you also teach, as stated in the US Department
of Energy’s Energy Literacy booklet, that “The total amount of energy in the universe is finite
and constant”? Unless you are also emphasizing that matter is a form of energy, then you are
teaching concepts from the 19th century.
To prepare our students to deal with the problems and opportunities of the 21st century, we need
to stop teaching the Conservation of Energy and the Conservation of Matter as separate laws. We
need to accept that the Law of Conservation of Matter became a subset of the Conservation of
Energy in 1905 when Einstein laid the foundation for his famous equation E=mc2. Matter can be
transformed into energy. It happens on the sun, where approximately 5 million tons of hydrogen
are converted to pure energy each second! ( http://solar-center.stanford.edu/FAQ/Qshrink.html )
It happens in atomic bombs and nuclear power plants as well. You can also turn energy into
matter, although that is much harder to accomplish! So do our K-12 educators teach that matter
is another form of energy? Unfortunately the answer is no.
The Next Generation Science Standards outline as Disciplinary Core Ideas the sequence in which
science concepts are taught. Following are the ones relevant to the conservation of matter and
energy. The first number within parenthesis indicates the grade at which the concept is taught.
PS1.A: Structure and Properties of Matter. The amount (weight) of matter is conserved when it
changes form, even in transitions in which it seems to vanish. (5-PS1-2)
PS1.B: Chemical Reactions. No matter what reaction or change in properties occurs, the total
weight of the substances does not change. (Boundary: Mass and weight are not distinguished at
this grade level.) (5-PS1-2)
PS3.B: Conservation of Energy and Energy Transfer. Energy cannot be created or destroyed, but
it can be transported from one place to another and transferred between systems. (HS-PS31),(HS-PS3-4)
PS1.C: Nuclear Processes. Nuclear processes, including fusion, fission, and radioactive decays of
unstable nuclei, involve release or absorption of energy. The total number of neutrons plus
protons does not change in any nuclear process. (HS-PS1-8)
From grades K-8 we are teaching our students concepts based on the work of James Joule in the
1840’s. We don’t bring them into the 20th century by revealing Einstein’s theory of relativity
until their high school physics class. But how many of America’s students take high school
physics? How can we expect our nation to understand and accept the potential of nuclear energy
if they lack even the basic understanding that matter is a form of energy?
I propose we make a small simple change that can remedy this problem. We combine the
separate laws into one single law: “Energy and matter can be neither created nor destroyed, but
they can be transformed, one to the other”. We can illustrate this with some simple math that
only requires students to be able to add and subtract decimals. Using the sun as an example,
students can find the sum of the masses of Deuterium and Tritium before fusion, and the sum of
the masses of Helium and a neutron after fusion. What happens to the missing mass? It turns into
the energy that warms your face and makes life possible on Earth.
Yes, this is nuclear physics, but it isn’t that complicated. Let’s change the way we teach about
energy, so our students are ready for the 21st century!