perfect mechanical systems in which there is only one force that practically does not exist.It is always a whole set of forces, such as gravity, friction, the floor reaction stretching, etc.Therefore, to determine which action in Newton test object, it is necessary to find the unit of the resultant forces.
resultant of all forces acting on the body, not a physical force.This is an artificial value that is entered for the convenience of calculation.However, we must remember that any force - it is a vector, which in addition has another scalar characteristics and direction.
not always right to talk about the resultant module as a simple summation
of all forces.This assumption is correct only if they are directed in the same direction.Then | R | = | f1 | + | f2 |, where | R | - resultant module, | f1 | and | f2 | - Modules individual forces.If f1 and f2 have the opposite direction, the resultant unit is equal to the difference between the highest and lowest power: | R | = | f2 | - | f1 |;| f2 | & gt; | f1 |.
Find resultant forces directed at an angle to each other, in a mechanical system can be using the methods of vector algebra.In particular, the rule of a triangle and parallelogram.In the first case, the start of perpendicular vectors combine the two joined forces and their end of the segment.The direction of this segment determines the greatest strength, and its length is similar to the hypotenuse in a right triangle by the Pythagorean theorem:
| R | = √ (| f1 | ² + | f2 | ²).
parallelogram rule used if the angle between the vectors of forces is different from 90 °.Then, in the calculations included the cosine and the unit of the resultant force is equal to the length of the diagonal of a parallelogram, which is obtained by placing the start of the second vector in the end of the other and carrying out parallel to them segments:
| R | = √ (| f1 | ² + | f2 | ² -2 • |​​ f1 | • | f2 | • cos α).