What is a forward movement? The school textbook clearly answers us with this question: translational movement of the body (note, an ideal object - “absolutely solid” - ATT, devoid of any possibility of being deformed!) - this is such a movement in which any line drawn inside the body (ATT) remains parallel to itself during the entire movement .
It would seem that the answer is comprehensive. A definition has been given, and the kinematics of translational motion is on the agenda. At first this is the simplest case of uniform rectilinear motion, then the more complex and interesting for inquiring minds equally variable (and again strictly rectilinear!) Motion, a striking example of which is the free fall of bodies. Under this section, the student gets acquainted with interesting patterns formulated as follows:
1. The paths traveled by the body for successive periods of time are correlated as the squares of the natural series of numbers : 1: 4: 9: 16 ...
and
2. The paths traveled by the body for equal consecutive intervals of time are correlated as a series of odd numbers : 1: 3: 5: 9 ...
When solving problems, there arises, within the framework of the necessary methodological and mathematical tools, an interesting method of reversibility of motion , in which all the final data becomes initial and vice versa (the movement seems to occur in the opposite direction, with a countdown). In terms of the dynamics of the inverse process, the instantaneous velocity vector at all points of the rectilinear trajectory change their direction in the opposite direction, only the direction of the acceleration vector genetically associated with the resultant vector of all the forces applied to the body remains unchanged.
The section "Dynamics of rectilinear motion" as well as kinematics, a priori implies that the motion of the body is strictly translational, without rotation around any axis and deformations. It is thanks to these predetermined conditions that the size of the body itself can be neglected under the conditions of tasks, considering instead an ideal object - a material point (MT) that spatially coincides with the center of gravity (CT) of the body. However, the MT object is introduced earlier in the Kinematics section for cases where the dimensions of the body can be neglected compared to the length of the trajectory.
Conservation laws in the case of rectilinear motion are also considered under the conditions when we abstract from the possible rotation of the body, considering its motion to be translational (otherwise we should consider the mutual transitions of the energy of rotational motion to the energy of translational motion and vice versa)
In short, the translational motion considered in the school course of physics (narrowly represented by a particular case of motion along a straight line!) Provides considerable food for theoretical reflection and research. This cannot be said about the experimental part of the section of the school course that studies translational motion. A high-quality experimental setup is simply not available in most school classrooms.
Even a special case of rectilinear translational motion is studied mainly in theory. A real, not a toy, Atwood machine is bulky and quickly incapacitated by inquisitive schoolchildren, being permanently installed somewhere near the far wall of the physics cabinet. Demonstration facilities, like a load sliding along a stretched wire, are completely meaningless, since they duplicate the self-sufficient case of rectilinear motion, which is by no means identical with translational motion in the most general case. What could be recommended here? Only a research search in the reality surrounding us outside the physical office using natural ingenuity!
The textbook example of a Ferris wheel ("Ferris wheel"), whose rim and spokes rotate and the observation cabs move progressively (albeit in a circle!) Convinces us that the translational motion of the ATT (and approximately the real body) can be not only rectilinear, but also have any curvilinear trajectory (in the above case, typologically coinciding with the trajectory of the rotational motion of the MT).
The idea of searching for cases of translational movement on a children's playground (in experimental mode, rather than theoretical reasoning) "lies somewhere near" the Ferris Wheel. Arriving at the playground, we can check whether the straight line (simulated by any twig or thin rail) remains parallel to itself when the body moves on all kinds of swings, carousels and trainers. It is clear that only the free fall of an inanimate body that has torn from some kind of "climbing frame" will be progressive.
Having made sure that in its pure form, translational motion is most often found in nature as a special case - translational rectilinear motion, we can move on to the theoretical material of the school textbook with a light heart.