movement of a body can be described, if there is a way to determine its position in space at each moment.To do this, you need to have a body of reference (to know about any other subject, we will consider his movement), as well as to establish for themselves the way we describe this movement.
the bodies have a size (ie, some extension in space), we need to decide in which cases we can not neglect them to trace the movement of each point.This is possible in two cases: if the body is moving in such a way that all straight lines drawn in it, make a move parallel to themselves (this is called translational motion), and if the size of the body in terms of the problem may be neglected (assumed body material point).This happens if the path traveled by the body is many times its physical size.
In mechanics, the default body is taken as a material point, unless otherwise specified.
line motion of a point in space - this trajectory.What it is?The concept of "trajectory", as defined by classical mechanics, involves the collection of all the provisions, consistently occupied a material point in space.
to determine the position, in the space occupied by the material at any given point of time, use the concept of the radius vector or coordinate system.The values of coordinates x, y, z describe points of a linear arrangement relative to the respective axes.Formula change of coordinates (or the position of the radius vector) and have the formula that is defined by its trajectory.
Since the movement is not only in space but in time, the third component of the reference system - a device for measuring time (clock or stopwatch).In conjunction with the coordinate system and the starting point (body count), they form the necessary "set" to describe the motion of our material point.Let
trajectory of an arc beginning at a point M1 which coordinates X1, Y1 and Z1, and ending at point M2 (coordinates X2, Y2, Z2).The distance that the material passes through the point of its trajectory (arc length | M1M2 |) will be called the length of its path.This scalar quantity.
If we draw from point to point M1 M2 directed segment (vector) r, then it will be referred to the movement of a material point.This notion - is not identical to the concept of the way.The path and moving points coincide only in the case of motion in a straight line.
kinematic law of motion (or a way to determine its origin at any time) is a function of time and can take an analytical view function coordinates or the radius vector of the variable t, indicating the movement.Its formula can be expressed as a table or a graph.
For uniform motion there is such a thing as the speed of the material point.Speed is the quotient of the amount of movement on the journey.If the trajectory of the - line, but the body is moving unevenly, t. E. At different speeds in different parts of the way, then we can talk about average speed.
In mechanics considers the motion of a different kind - uniform rectilinear, uniformly accelerated rectilinear and uniform around the circumference.
Features mechanical movement relative movement can be seen in two or more coordinate systems, some of which are fixed, others are moving.For example, the vehicle is driven on the road with respect to walking on it as a pedestrian (fixed point), which itself is moving with respect to the growing of a tree beside the road (a fixed point of reference).In this case, the speed of the body (of the car) will consist of two speeds - its rate relative to the first - mobile - system (pedestrian) and walking speed relative to the fixed (wood).
