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x  x  t

y  y   t

z    t z
(1.2)

which describe the changes of point's coordinate as a function of time.

These equations are called cinematic equations of motion. At the same
time space position of the material point (balloon in fig.1.5) is

described by radius-vector r , which connects the origin of the frame

of reference 0 with the material point :

  
r  x i  y j  z k
   , (1.3)
where i , j, k - unit vectors.
The curve described in space by the moving point is called trajectory.

Vector of displacement of a
material point is the vector that
connects the point 1 of the

initial position with the point 2
of the final position of the
material point. In fig.1. 5 we

can see the trajectory like a
mountainous road, where the
vector of displacement connects

the initial and final position of
Figure 1.5
the car on this road.
If fixed trajectory is known,
space position of material point on this trajectory can be described by

distance-time function
S  S (t ) (1.4)

Where S is the path length (or distance traveled) i.e.- the distance
measured along a trajectory in the direction of point's movement.

1.3 .Speed and Velocity

We often use terms speed and velocity. It seems that these terms
are similar. But from the point of view of the physics there are sharp
distinctions between these terms.

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