ENERGY

I. Energy

Energy is the ability to do work. The fundamental forms of energy are rest energy, potential energy, and kinetic energy.

The Rest Energy is , where is the rest mass (the mass of an object at rest). The rest energy of an object of rest mass is the energy obtained when its rest mass is entirely converted into energy according to the above formula.

The Potential Energy (or configuration energy) of a system held in a particular position (or configuration) is the work that will be done if the system is released. (Oh, note well that in physics, work is energy.)

Work and heat are other forms of energy, but they are not fundamental forms. Similarly, electrical, chemical, wind, gravitational, biological, solar, etc. energies.

An Example of Potential Energy: Gravitational Potential Energy

Examples of Potential Energy: Elastic Potential Energy

The Potential Energy in figures a, b, and c are:

The Kinetic Energy is the energy an object has by virtue of its motion. The kinetic energy of an object of mass m moving at a velocity v is , for pure transitional motion.

For transitional and rotational motions combined.

II. Total Mechanical Energy

The Total Mechanical Energy of an object is the sum of its kinetic and potential energies, .

III. Work: Work is energy. It is of the nature of a force times a distance!

l The work done by a constant force parallel to the displacement is .

l For F constant but not parallel to displacement.

l In general, the work element is . One gets W by integration! This always applies-- whether the force is constant or not. (To be continued in college!)

Conservative and non-conservative Forces

A conservative force is a force whose work

does not depend on the path it follows; it

only depends on the departure and arrival

points.

A non-conservative Force is a force whose

work depends on the specific path it follows from

the departure to the arrival points.

for a non-conservative force-- such as a friction force.

Frictional forces are always non-conservative forces. So are "air resistance", "fluid resistance," i.e., drag, forces.

Work - Energy Theorem

Let be the total mechanical energy of an object at position one (1). Let be its total mechanical energy at position two (2). The change in the total mechanical energy, from position one to position two, is .

Work - Energy Theorem: The change in the total mechanical energy of a system (or object), from position one to position two, is equal to the work done on the system (or object) by the non-conservative forces.

Law of Conservation of Energy: When the work done on a system by non-conservative forces is zero, then the total mechanical energy of the system is conserved (i.e., constant).

Assginment: (a) Using dictionaries, encyclopedia, and other materials (in books, journals, maganizes, or at web sites), make as an exhaustive list of the forms of energy as possible. Number these forms of energy. (b) Draw a three column table for rest, potential, and kinetic energies. Place in column, using a row per form of energy, the numbers of the common forms of energy that belong to the respective column. Example: the row for wind energy, the number for wind energy will be place under kinetic energy (wind energy is entirely of this fundamental form, so is heat energy). (c) The extraction, utilization, storage, transportation, and consumption of energy account for a great deal of all environmental problems. Explain this point by elaborating on it.