Version 1.0, August 31, 2001, Copyright, Hugh Jack 1993-2001

3.1 SOME BASIC CONCEPTS

 

· Mass and force - A mass can exert forces through gravity and other effects. Forces can also be exerted by other phenomenon, such as magnetism.

 

· We can emphasize the relationship between mass as an absolute and gravity as a local. The effects of gravity are dealt with as forces in most statics problems.

 

 

· Force has magnitude and direction. Therefore it is well suited to vectors.

 

· many forces can also operate on the same object, we can replace these with equivalent forces, called resultants.

 

 

· We have both action and reaction forces as well. As we apply action forces, there are forces that will resist, these are called reaction forces.

 

· Some approximations,

  1. - we are pretending the forces are applied at points, but in reality a force must be distributed,
  2.  
  1. - we generally assume there are no deflections. This is known as the RIGID BODY assumption.
  2. - we often use particle approximations that assume bodies have no size. This simplifies calculations significantly.
  3. - Transmissibility - a force can be moved along a line of action.
  4. - Parallelogram law - a method for adding two forces to get a resultant vector.