Chapter 13: Work and Power

Work and Energy

Energy is one of the most important unifying concepts in all of the physical science.
Conservation of energy states that in any isolated system the total energy of all forms is constant
* Conservation laws play a vital role in all of physical science.
* Conservation of mass: Matter cannot be created or destroyed.
* Kinetic energy is energy associated with mass in motion.
* Conservation of energy can be generalized to include energy associated with every kind of physical phenomenon.
* Force acting on a body does work on the body only when the body moves.

* Work Wk = when a body moves a distance s along a straight line while a constant force of magnitude F, directed along the line, acts on it.

* The work W done by this force when its point of application undergoes a displacement and the component of the force in the direction of the displacement.The componenet of F in the direction of s is F cos@ .Then

W = (F cos @) s


* Alternative interpretation:
W = F s

* Work is a scalar quantity, even though force and displacement is vector.
* When force and displacement are perpendicular, the force does no work.
* The joules is the unit of work and of energy of all kinds.

Scale for work

1 joule = (1newton) (1meter)
1 J = 1Nm
1 dyn = 10-5
1cm = 10-2
1J = 0.7376 ft.lb
1ft.lb = 1.356 J