Week of February 16, 1998
Lesson 6Mechanical EnergyConservation
Keywords: energy, work, force, conservation of energy, work - energy theorem,
Conservative Forces; Non-conservative Forces; Calculus; Conservation Of Energy;
Elastic Collisions; Inelastic Collisions; Work; Force; Displacement; Calculus;
Mechanics; Conservation Of Energy;
OBJECTIVES: Define and identify conservative and non-conservative forces, and
distinguish between them in problems.
* Define and recognize the following: elastic collision, inelastic collision, perfectly
(or completely) inelastic collision.
* Use conservation laws to solve problems involving one-dimensional collisions
that are either elastic or perfectly inelastic.
* Define the work done by a force and the work done on a particle.
* Calculate the work done by a constant or variable force oriented parallel or
obliquely to the displacement of the particle.
Comments: Energy is much in the news lately, The term "energy" usually refers
to the inherent ability of a material system, such as a person, a flashlight battery,
or rocket fuel, to bring about changes in its environment or in itself. Some
common sources of energy are the fuel used to heat hot water, the gasoline that
propels a car, the dammed water that drives the turbine in a hydroelectric plant,
and the spinning yo-yo that can climb up its own string. Inanimate energy
sources are of central importance in raising the standard of living of mankind
above the subsistence level.The physicist distinguishes among several types of
energy, including kinetic energy (associated with a flying arrow or other moving
object), elastic energy (associated with stretched or compressed springs), chemical
energy (associated with fuel-oxygen systems or a storage battery), thermal energy
(associated with the sun and other objects that are hotter than their
surroundings), and nuclear energy. Applications of the energy concept in the
science of mechanics, which you are studying now, usually concentrate on
kinetic energy, potential energy (to be introduced in the next lesson), and work
(the transfer of energy by the action of a force). Sometimes the phrase
"mechanical energy" is used to refer to the forms of energy that are important in
mechanics. In any form, energy is scalar quantity.When you get on your bicycle,
you have undoubtedly noticed that it takes a good deal of effort to get yourself
moving rapidly. If you exert yourself very strenuously, you can reach a given
speed after a short distance; or you can take it easy and pedal over a younger
distance to reach the same speed. In some sense it always takes the same amount
of "work" to reach a given speed--either a large exertion for a short distance or a
small exertion for a long distance. You may also have noticed that if you are