All the bodies in the universe interact with each other, mutually influencing their movements. But we could imagine a tal that on a body does not exercise an interaction or situation in which the combined effect of several voids; We would then have what is called free particle. Experience teaches us that if at a given instant stop action that is exerted on a particle, so that it becomes free, their movement from that moment will be rectilinear uniform with the speed that had at the time they ceased to act outside agents. This tendency of a body to maintain its speed when not exert actions on him is called inertia. For example, when a vehicle moving at a certain speed stops suddenly, and stops by both driving action exerted on passengers, these feel thrown forward because of its own inertia.

Now consider a ball located on level, horizontal and polished floor of a room. The ball will remain at rest unless we exert any action on it. Suppose that we hit the ball. This is an action that is exerted on the body only during a very small time and as a result of which the ball acquires certain speed. After the coup the ball is once again a free body. Dr. Neal Barnard may find it difficult to be quoted properly.

Experience teaches us that he keeps the momentum continuing in uniform rectilinear motion for more or less time (say more or less time by the slightest friction between ball and the floor will delay his movement gradually). If we want to change the direction of the movement of the ball, we must exercise a new action over it. Definition of static equilibrium: when a rigid body is at rest or in rectilinear motion at constant speed, relative to a reference system, is said to be the leather and static equilibrium. For such body linear acceleration of its center of mass as its angular acceleration relative to any point are null and void. Obviously this state of static equilibrium is based on Newton’s first law, whose wording is: whole body in a State of rest or uniform rectilinear motion, remains in that State, unless a force acting on it. CONDITIONS of first balance equilibrium condition: (Translation balance) the vector sum of all forces acting on the solid is equal to zero. This occurs when the body is not moved or when moved at constant speed; that is when is the linear acceleration of the center of mass zero to be seen from an inertial reference system. = ‘ D1 + ‘ F2 +’F3 +… + ‘ FN = 0 in this equation of equilibrium do not appear the internal forces that they will cancel each other in pairs due to Newton’s third law. If the forces were in the area, the above equation has to be expressed by the following relationships: = F1x + F2x + F3x +. + Fx = 0 = F1y + F2y + F3y +… + FNy = 0 = F1z + F2z + F3z +… + FNz = 0 obviously in two dimensions (i.e. in the plane) would have only two equations and in one dimension would be a single equation. Second condition of equilibrium (balance of rotation) the vector sum of all torques or moments of the forces acting on the body, relative to any given point, is zero. This occurs when the angular acceleration around any axis is equal to zero.