Environmental Engineering Reference
In-Depth Information
1
ENERGY
The Basic Concepts
What are forces?
In order to live and move around, human beings need to overcome gravity, or the
force of attraction that the Earth exerts on all objects. They must also overcome
other obstacles to movement, such as friction. With muscular effort, humans man-
age to overcome such obstacles and thus lift bodies or set them into motion. There
are a variety of forces in nature, aside from the force of our muscles.
Isaac Newton (1642-1727) named force any agent capable of causing bodies to
move. He established a relation that determines the amount of force necessary to
cause a certain movement:
force (F) = mass (m) × acceleration (a).
Forces are measured in newtons (N). The gravitational force on 1 kilogram (kg) of
matter is 9.8 N.
Frequently, it is not enough to apply a force to a body to make it move. For
example, the horses that pull a wagon must also overcome the friction that exists
between the wagon and the road.
What is work?
When an object falls from a given height above the surface of the Earth, the force
of gravity (F) results in a quantity of work (W) defined as the product of the force
and the distance the object travels (d):
work (W) = force (F) × distance (d).
The unit commonly used for work is the joule (J), which is the energy needed to
lift a small 102-gram (g) apple 1 meter (m) against the Earth's gravity.
 
Search WWH ::




Custom Search