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Axis of rotation lever problem

Specious these ideas and explain exactly right? the teachers suggested that he], the following issues for further consideration, and then judge.
  (1 of the whole device can be as leverage? how to understand leverage "arm" concept?
  2 arm respectively?
  (2) friction, and stretch on device of balance what has no effect? how with more has persuasive of experiment be proved? students in teacher of guide Xia, carried out has further of experiment and analysis, antibody for following two species case: Dang around on both sides hook code of number not equal Shi, anyway changes, are cannot makes loaded balance; Dang around on both sides hook code number equal Shi, anyway changes, are can makes loaded au balance. Students of awareness in-depth a step: on Figure 3 by shows of loaded,, if according to by shows problem of method to for research, to device in the for fixed turned axis, then role in another a hinge Shang of stretch, should is a makes lever (to, for fixed hinge) clockwise turned (and, of role effect instead) of force, and with of changes and changes, to up to makes device balance of role. However the reality is not so: codes are not equal to the number of left hooks, devices for balance, and always to the side of the hook code number down until quadrilateral turning boxes cannot "turn". So you can infer that the problem cannot simply be treated as shown as shown in two axis of rotation of the lever handle.
  Early explicit clues a original seems simple of experiment, was appeared __ such surprised everyone expected of problem, for unlock confused, many students to people ask, and to library or network Shang looking for related information, then expand more in-depth of discussion, students gradually awareness to, by shows of problem in the, whole framework itself has 4 a turned axis, not a root "hard rod", also on insufficient a root lever. Because the entire attire Qu has two fixed hinge and the 4 sides of the frame can be seen as a "hard stick", so the framework can not rotate, but only in certain cases deformation and always maintain vertical finishing, beams remain horizontal and, edge, the rotation is the same, as shown in. However, the cause of the entire device can be turned on, is still unknown. However, according to some students put forward their own inferences.
  (1) the description of the two cases, the device can turn the left and right sides of the hook code decides the number of, and hung by the hook code regardless of where! is it means that the beam does not work then?
  (2) when the "left hook code number when devices balance does not equal the imbalance." This and balance of situation same this is can said, whole loaded although not a root "hard rod", but is has, arm lever of characteristics! this a views makes students feel answers seems to away from they has not far has! according to device of symmetric sex and experiment phenomenon, they bold to proposed following assumed by shows of device can as is by quadrilateral framework constitute of, arm lever, around on both sides of beam not works! say, and of arm should is as in the by shows of, and non-in the by shows of, and by hinge, and on both sides strictly symmetric, so. For each of these situations can give a more satisfactory explanation. Students to design the experiment as shown in Figure 7: left hook code removed, hang a bucket, into small bins and fine sand is used for the research, if you are still around only when both sides maintain a balance equal to the total mass of fashion, are explained more fully to the above question experimental evidence. From the experimental data (table) draws the following conclusion:
  Hook code number, the less quality smaller lever kegs and when the total mass of sand or smaller lever left and right sides of the poor quality of the smaller-~ and mass-difference should the mass difference.
  Different bearings, friction of moving parts of the entire load is smaller, the balance lever left and right sides of the poor quality of the smaller.
  Crotch rubbing force of moving parts when the device is small enough to be neglected, combined with the preceding analysis, no matter how the location of the hot spot beam, shown with Ambrose can be seen as made up of quadrilateral turning box bascule. Out base Xia above experiment and analysis, students formed has following explained residence shows of loaded in the, fierce for left beam and is a overall (remember for "part"), it above of each one points of movement situation and beam (or) of hinge (or) of movement situation same, so role live "part" Shang of each one points of force, as long as direction same, its arm are equal, that beam part not acts as a arm, objects hanging in where does not effect experiment of results. Right beam and the overall situation is similar. Therefore, the arm should be as shown, by the symmetry of the rotation system of hip-Traction case small enough, the entire load can be seen as equal arm lever. To support their hypothesis, they also designed the apparatus shown at this time as long as the entire appliance is able to maintain a balance, with an axis of rotation lever is exactly the sa BACK

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