Instruction

1

Speed is one of the characteristics of motion of a material point. It expresses the distance traveled by this point during a specific period of time. Distinguish between average and instantaneous speed and uniform and non-uniform motion.In uniform motion velocity not changes with time, which facilitates the determination of the direction of this

**velocity**vector by. The vector average**velocity**is the ratio of the increment of the radius vector to the time interval:[v]=?r/?tНаправление the radius vector ?r coincides with**the direction**m of the average**speed**as shown in Fig.1, as the point is moved from point M to point M1. This condition is observed only by the uniform motion of a point.

2

Instantaneous velocity is calculated when ?t tending to zero. This is a vector quantity equal to the first derivative of the radius-vector on time. It is calculated as follows:v =|lim ?r/?t|=ds/dt

?t>0Вектор instantaneous

?t>0Вектор instantaneous

**velocity**is tangential to the trajectory of the MM1. Integrating the last expression for ds gives:s=v?dt=v*(t2-t1)=v*tПоследняя formula applies in the case of uniform motion, when the condition of the problem given time.3

The direction

**of the velocity**can only be computed by coordinate method, since it is a vector quantity.If the task is assigned to x and y coordinates are shown, and indicated the projections vx and vy may be determined as a numerical value**speed**and its**direction**. The vector**velocity**v in this case is the diagonal of a square formed by two projections. Consequently, the velocity is:v= sqrt(vx^2+vy^2), where tg?=vx/vy (see Fig.2)it Should be noted that in real conditions on the moving body acts a number of factors: friction, gravity, etc. In some tasks, the influence of these factors can be neglected, in others at least some of them should be considered mandatory.