Guide
1
First you need to understand that the resultant force depends on the condition of the body.If the body is at rest, then it acts the two forces.Gravity pulls the body down.Also, being on any surface in the body acts reaction force, which is directed vertically downwards.If you find the resultant force F = Ft + (- N) = 0.Reaction force is directed opposite to the force of gravity, so it is taken with a minus sign.Consequently, a body that is at rest, has resultant force zero.
2
Let us consider a situation where on the body side impact force that causes the body to come into motion.Force vecto
r is in the first instance is directed perpendicular to gravity.Then the body of the four acts of force.Gravity, reaction force, friction force and thrust force, which causes the body to move.Knowing that the reaction force is equal mg, and opposite to the force of gravity, their resultant zero.Consequently, the resultant is equal to the difference between the forces of friction and traction.
3
In the case where the body makes moving force that is at an angle to the floor reaction force.You must enter a countdown on the x-axis, which is directed towards the movement.The friction force is taken with a minus, while the thrust will be calculated in accordance with trigonometry.Vectors reaction force and traction, form a triangle, the angle between the cosine of which is taken over as party vector support reaction adjacent to the corner and thrust vector is the hypotenuse.Consequently, the reaction force will be expressed by the formula cosA * F.Knowing that the reaction force mg, will traction force and the resultant , which is aimed as a pulling force.