Progressive movement

What is the forward movement? The school textbook clearly answers this question to us: the translational motion of the body (Note that an ideal object - an "absolutely rigid body" - ATT, devoid of any possibility to be deformed!) Is a movement in which any straight line drawn inside the body (ATT) remains parallel to itself during the entire movement .

It would seem that the answer is exhaustive. The definition is given, and the kinematics of translational motion is on the agenda. Initially, this is the simplest case of uniform rectilinear motion, then a more complex and interesting for the inquisitive minds of an equally variable (and again strictly straightforward!) Movement, a vivid example of which is the free fall of bodies. Within the framework of this section, the student acquaints himself with interesting laws, formulated as follows:

1. The paths traversed by the body in consecutive intervals of time, correlate as squares of the natural number of numbers : 1: 4: 9: 16 ...

and

2. The paths traversed by the body for equal consecutive intervals of time, are related as a series of odd numbers : 1: 3: 5: 9 ...

In solving problems, a curious method of reversibility of motion arises, in the framework of the necessary methodological and mathematical tools, in which all the final data become initial and vice versa (the motion as it happens in the opposite direction, with a countdown of time). In terms of the dynamics of the inverse process, the instantaneous velocity vector at all points of the rectilinear trajectory reverses its direction, only the direction of the acceleration vector, genetically related to the vector of the resultant forces applied to the body, remains unchanged.

The section "Dynamics of rectilinear motion", just like kinematics, a priori implies that the movement of the body is strictly translational, without turning around any axis and deformations. It is due to these previously agreed conditions that the dimensions of the body itself can be neglected under the conditions of problems, considering instead an ideal object - a material point (MT) spatially coinciding with the center of gravity (CT) of the body. However, the MT object is introduced earlier in the section "Kinematics" for cases when the dimensions of the body can be neglected in comparison with the length of the trajectory.

Conservation laws in the case of rectilinear motion are also considered under conditions when we abstract from the possible rotation of the body, assuming its motion is translational (otherwise it would be necessary to consider the mutual transitions of the energy of the rotational motion into the energy of the translational motion and vice versa)

In a word, the forward movement considered in the school course of physics (narrowly represented by a particular case of motion along the straight line!) Provides considerable food for theoretical reflection and research. What can not be said about the experimental part of the section of the school course studying the translational motion. A qualitative experimental setup is simply missing in most school cabinets.

Even a particular case of rectilinear translational motion is studied primarily in theory. The real, not toy, Atwood machine is cumbersome and quickly disrupted by inquisitive schoolchildren, being permanently installed somewhere near the far wall of the physics room. Demonstration installations like sliding along the tensioned wire are completely useless, since they duplicate the self-contained case of rectilinear motion, which is by no means identical to the forward motion in the most general case. What could I recommend here? Only a research search in the reality around us outside the physical cabinet with the use of natural wit!

The example of the Ferris wheel ("Devil's Wheel") cited by the textbook, the rim and spokes of which rotate, and the observation booths move translationally (albeit along the circumference!) Convinces us that the translational motion of the ATT (and approximately the real body) may be Not only rectilinear, but also have any curvilinear trajectory (in the given case, typologically coinciding with the trajectory of the rotational motion of the MT).

The idea of finding cases of translational motion on a children's playground (in the mode of experiment, rather than theoretical reasoning) "lies somewhere near" with the "Devil's Wheel." Coming to the playground, we can check whether the line itself remains parallel to itself (modeled by any twig or thin rod) when the body moves on all kinds of swings, roundabouts and simulators. It is clear that the free fall of an inanimate body, which has fallen from some "climbing chamber", will be forward only here.

Convinced that in the pure form the translational motion is most often found in nature as a special case - a forward rectilinear movement, we can easily pass to the theoretical material of the school textbook.