Fundamental Forces of Nature
in nature may be classified into four types. The gravitational
force holds together the universe at large, plus the atmosphere, water,
and us to the planet Earth. The electromagnetic force governs atomic
level phenomena, binding electrons to atoms, and atoms to one another
to form molecules and compounds. The strong nuclear force holds
the nucleus together. The fourth force, the weak nuclear force,
is responsible for certain types of nuclear reactions and has little bearing
on energy sources today.
shows the four forces, the property on which each acts, and examples of
each force. Gravitation and electromagnetism are the two forces with which
we will be primarily concerned, as these are the two forces that operate
at the macroscopic level of environmental systems. These also currently
form the basis of our most prevalent sources for energy technologies.
The strong nuclear force is the strongest of the forces. Nuclear fusion
reactions on the surface of the sun are the result of the nuclear strong
of object near a planet; force that keeps planets in their
orbits around the sun
that keeps an electron in its orbit around the atomic nucleus; (i.e.,
attraction or repulsion between a “charged” plastic comb and
a strand of hair)
that keeps protons and neutrons together in a nucleus
responsible for certain types of nuclear reactions
7: The four fundamental forces (or, interactions) and the properties
on which they act. *Spin and isotopic spin are properties of elementary
particles that we will not define here.
four “sources” of energy and identify the force responsible for the
energy transformation. For example, a hydroelectric plant has a waterfall
for its source, and the force responsible is gravitation.
What fundamental force is responsible for (a) wind, (b) solar, (c)
tidal, and (d) nuclear energy? Explain your reasons.
that we experience belongs to one of these four categories, even when
the connection is hard to see. The force of friction, for example, is
an electromagnetic force. The force of the explosion of a chemical explosive
is also electromagnetic in origin. The energy of an atomic bomb (more
correctly, a nuclear bomb) is released as a result of the action of strong
occur when matter changes position or matter changes state in the presence
of these forces. What we call energy "production" is really
energy transformation -- that is, energy is converted from a potential
form to a form available to us for use.
of force acts on a specific property of an object. The specific property
refers to the aspect of an object that is necessary for that object to
be influenced by the force -- or "to feel" the force. For example,
gravitation acts on the mass of an object. Strictly speaking, as an object
fall towards the Earth, the Earth is falling towards the object. Because
of the mass difference, the total effect of the Earth on the object is
much more than that of the object on the Earth. However, the gravitational
force on each kg of Earth is the same as on each kg in the object.
In the case
of the electromagnetic force, the object must have an electric charge.
But if that object has no net electric charge, then an outside source
of electromagnetic force cannot exert a force on that object. The space
in which a force is felt is called the "field" of the force.
Thus all objects on Earth are in Earth's gravitational field, the planets
and moons are in the sun's gravitational field, as well as in their mutual
and Kinetic Energy
Whenever we say that we are producing energy, what we really mean is that
we are transforming energy from one form to another that is more usable.
For example, water at the top of a waterfall has more gravitational potential
energy than when is at the bottom of the waterfall, because the water
at the top is further from the center of the Earth than at the bottom.
So, if the water is allowed to fall from the top to the bottom, (that
is, the Earth's gravitational force does work on the water moving it),
then the energy stored as potential energy at the top becomes transformed
into the kinetic energy of this water and we can use it to do work. This
is the principle behind the production of hydroelectric power.
each of the following cases, trace the chain of energy
transformations from the sun to the energy in its final form:
pot of water is boiled on an electric stove.
100 nt automobile accelerates from rest on a level road, climbs
a hill at constant speed, and comes to stop at a traffic light.
windmill pumps water out of a flooded field.
energy, therefore, is the energy associated with different positions in
the force field. The water at the top of a waterfall has higher gravitational
potential energy than at the bottom because of the different positions
in the gravitational field. Consider two points (A and B) in the Earth's
gravitational field (g) where B is h meters higher than
A. Then a mass (m) has a potential energy mgh higher than
its potential energy at A. At a point 2h above A, the mass has
a potential energy of 2mgh. So height is a measure of the potential
analogy with water and gravitational potential energy gives us a way to
represent energy levels showing the potential energy state of a system
in terms of horizontal lines. Thus we could say that the 100 m point above
the lowest level in a waterfall has 980 Joules gravitational potential
energy per kg of water above the lowest point.
* g * h = E (Energy)
kg * 9.8 m/sec2 * 56 m = 549 J
12: Energy Levels Diagram (gravitational).
also demonstrate that potential energy is a representation of the position
of a system in a field of force. The 1 kg of water in our example has
higher potential energy when it is further away from the center of force
(center of the Earth). At point A, the water is more "bound"
(to the Earth) than at point C. We will use this idea later to draw the
analogous levels to represent chemical potential energy.