Speed - the characteristic of the movement of a body characterizing speed of its movement, that is, the distance passed by it per unit of time. This parameter is vector, so, has not only the size, but also the direction. It is required to define the direction of speed in a number of physical tasks.
Instruction
1. Speed is one of characteristics of the movement of a material point. It expresses the distance passed by this point for certain interval time. Distinguish the average and instantaneous velocity and also uniform and non-uniform motion. At uniform motion the speed does not change eventually that facilitates definition of the direction of this speed in the vector way. The vector of average speed represents the increment relation radius vector to a period: [v]? r/? tnapravleniye radius vector? r coincides with the direction of average speed, as shown in fig. 1 as the point moves from Paragraph M to M1 point. This condition is met only at uniform motion of a point.
2. Instantaneous velocity pays off at? t, tending to zero. It is the vector size equal to the first derivative radius vector on time. It pays off as follows: v = | lim? r/? t | =ds/dt? t> 0 The Vector of instantaneous velocity is directed on a tangent to a trajectory of movement MM1. Integrating the last expression on ds, we will receive: s=v? dt=v * =v*tposlednyaya a formula is applied (t2-t1) in case of uniform motion when in a statement of the problem the period is given.
3. The direction of speed can be calculated only in the coordinate way as it is vector size. If in a task coordinates x and y are set and also specified projections of vx and vy are specified, both the numerical value of speed, and its direction can be defined. V speed vector in this case is the diagonal of the square formed by two projections. Thereof, speed is equal: v = sqrt(vx^2+vy^2), where tg? =vx/vy (see fig. 2) Should consider that in actual practice the moving body is affected by a number of factors: friction, gravitation, etc. In some tasks the action of these factors can be neglected, in others at least some of them need to be considered without fail.