What Forces Conserve Energy and What Is the English Unit of Force?

[Poy]

Are all forces vectors? What forces do and don't conserve energy? What is the English unit of force? Its one of those little web search things, and some of those aren't so easy to find...

 

[Thomas Becker]

Hi, Poy,

Yes, forces are vectors, they are only completely described by giving them a length and a direction,

where we come to the question of energy:
it depends on the movement, displacement produced by the force.
If the body the forces acts on
1) is not deformed or moved --- no work is done, no change in energy.
2) moves perpendicular to the direction of the force --- no change in energy.
but
3) moves, but not perpendicular to the direction of the force, or is deformed against its inner "springs" --- there is some work done by the force and energy changes (at least, it transforms from potential to kinetic energy or temperature, depends whther the actor of the force belongs to the system).

Thomas
:-)

 

[HallsofIvy]

Yes, all forces are vectors. If you have a very artificial problem where you know everything will be in a straight line, you can set up your coordinate system so that the x-axis is along that line and ignore the other components, but the force really is a vector still. If a force depends only on position and not on such things as the speed with which an object is moving are conservative.

The English unit? You mean the one that the English don't use any more and only us silly Americans do? The pound. The corresponding unit of mass- the mass that on the surface of the Earth would weigh 32 pounds is called a "slug". (In the English system the acceleration due to gravity is about 32 ft/s² so the slug is a "unit" mass.) Unfortunately a lot of people also use "pound" when they really mean a "slug".

 

[Poy]

Lots of thank