Legend

 W = work F = force d = distance KE = kinetic energy PE = potential energy
The roller coaster in the picture contains both potential energy and kinetic energy.  And these two energies are constantly transforming from one to another.

Work & Energy

Unbalanced forces cause objects or systems to move, change direction or speed; once this happens, work is done.

 W = F||d W = work done (Joules, J; 1 J = 1 Nm)  F|| = force parallel to the direction of movement (N) d = distance

Energy
is the ability to do work.  It comes in many forms, solar, chemical, mechanical, heat, electrical, etc.  Though each is a form of energy, each is defined slightly differently.  We are mainly concerned with these types:

Kinetic Energy (KE) and Potential Energy (PE).

If the forces do not result in movement or change in direction or speed, NO work is being done!  The strain you feel comes from the upward force you exert to balance the downward force of gravity.

The work being done in moving an object from one position to another does not depend on the path it took; regardless of how an object gets from A to B, the same amount of work is done.

This is true only if the forces are conservative (energy is not lost through them).   Example, spring, gravity are conservative and friction is not.

The work-energy principle is a general statement that relates the work done on an object due to a change in its energy.  the net work (Wnet) done o an object is the sum of all work done by conservative forces (Wc) and non-conservative forces (Wnc).

Wnet = Wc + Wnc

since

Wnc = KE = 1/2 mvf2 - 1/2 mvi2
and
Wc = PE = mghf - mghi

So,

Wnet = KE + PE

If every kind of energy was considered (from both conservative and non-conservative forces) in the work being done to an object, the total energy before and after in that object is the same; this is The Law of Conservation of Energy.

The total energy of any system that is isolated from the rest of the Universe remains constant, even though energy may be transformed from one kind to another within the system.
Sum of all energy before = Sum of all energy types after.

 Dynamics Kinetic Energy

 created by Will Kuo and Stan Watterson thinkquest participants  team 25844 ©1999 Eloquent Logic. All rights reserved.