CN114373368A

CN114373368A - Demonstration lever for accurately reading force arm

Info

Publication number: CN114373368A
Application number: CN202111639007.4A
Authority: CN
Inventors: 孙丽娟
Original assignee: Individual
Current assignee: Individual
Priority date: 2021-12-29
Filing date: 2021-12-29
Publication date: 2022-04-19

Abstract

The invention relates to the technical field related to physical teaching equipment, in particular to a demonstration lever for accurately reading a force arm, which comprises a base, wherein a supporting rod is fixed on the upper end surface of the base, a limiting component for limiting the lever is arranged in the supporting rod, a central block is arranged on the front side of the supporting rod, a scale plate is fixed in the central block, two sliding blocks are arranged on the periphery of the scale plate, and the two sliding blocks are arranged in a left-right symmetrical mode by taking the central block as a center; according to the invention, the weights are hung through the hooks on the left side and the right side, when the weights are hung, the rotating angle of the scale plate is small due to the limiting effect of the limiting block, so that a demonstrator can conveniently hang the weights, and meanwhile, when the scale plate is horizontal, the limiting pin is clamped into the limiting cavity, so that the scale plate cannot rotate, the degree is convenient, the explanation of the demonstrator is also facilitated, and the unit of the front end surface of the scale plate is further subdivided through the dial, so that the test result is more accurate.

Description

Demonstration lever for accurately reading force arm

Technical Field

The invention relates to the technical field related to physical teaching equipment, in particular to a demonstration lever for accurately reading a force arm.

Background

The demonstration lever is one of important equipment for demonstrating the lever principle and enabling students to understand the lever theorem more vividly as common equipment for physical teaching.

But traditional demonstration lever structure is generally comparatively simple, mainly constitute by a lever and two sets of weights, when the demonstration teaching, because traditional lever rotation range is unable spacing, thereby lead to when hanging the weight, the demonstration personnel need hold up the lever, thereby avoid the lever upwarping, thereby influence the teaching explanation, simultaneously because traditional demonstration lever, in order to keep the lever balanced, the demonstration personnel can hang the weight of both sides about in suitable position, thereby it never balances to balanced a gradual change process to lead to not have the lever, and then make unable fine embodiment change along with the lever arm of force, the process that the effort changed on it, it is relatively poor to lead to lever principle demonstration effect, and traditional demonstration lever degree of force accuracy is lower, the test result precision is low.

Disclosure of Invention

The invention aims to provide a demonstration lever for accurately reading a force arm, which is used for overcoming the defects in the prior art.

The demonstration lever capable of accurately reading the force arm comprises a base, wherein a supporting rod is fixed on the upper end face of the base, a limiting assembly used for limiting the lever is arranged in the supporting rod, a central block is arranged on the front side of the supporting rod, a scale plate is fixed in the central block, two sliding blocks are arranged on the periphery of the scale plate, and the two sliding blocks are arranged in a bilateral symmetry mode by taking the central block as a center;

spacing subassembly including set up in axle sleeve in the bracing piece, normal running fit has the sliding block in the axle sleeve periphery, be provided with the spacer pin in the sliding block, the spacer pin is located the axle sleeve upside, be equipped with the ascending spacing chamber of opening in the axle sleeve, the axle sleeve downside is fixed with the spacer block, be provided with the pin in the sliding block, the pin is located the stopper downside.

As a further scheme of the invention, a sliding block cavity is arranged in the support rod, the sliding block is in sliding fit with the sliding block cavity, a limiting pin sliding cavity with a downward opening is arranged in the sliding block, the limiting pin sliding cavity is positioned on the upper side of the shaft sleeve, the limiting pin is in sliding fit with the limiting pin sliding cavity, a limiting pin spring is fixed between the upper end surface of the limiting pin and the upper end wall of the limiting pin sliding cavity, the limiting pin sliding cavity and the limiting cavity can be communicated, when the limiting cavity is positioned on the lower side of the limiting pin sliding cavity, the limiting pin can be inserted into the limiting cavity, and the scale plate cannot rotate any more under the limiting action of the limiting pin so as to facilitate the degree test.

As a further scheme of the invention, an arc-shaped cavity is arranged outside the shaft sleeve, the limiting block is in sliding fit with the arc-shaped cavity, a return spring is fixed between the sliding block and the lower end wall of the sliding block cavity, a pin sliding cavity with a backward opening is arranged in the sliding block, a pin cavity is communicated with the rear side of the sliding block cavity and is in sliding fit with the pin sliding cavity, when the pin cavity is positioned at the rear side of the pin sliding cavity, the pin can be inserted into the pin cavity, a pin spring is fixed between the pin and the bottom wall of the pin sliding cavity, a pull rope is fixed between the front end surface of the pin and the upper end surface of the limiting pin, and the up-and-down movement of the limiting pin can be realized by utilizing the left-and-right movement of the pin.

As a further scheme of the invention, the front side of the sliding block cavity is communicated with a shaft sleeve cavity with a forward opening, the front side part of the shaft sleeve extends forwards to penetrate through the shaft sleeve cavity to the outside of the supporting rod, a bevel gear shaft is rotationally matched in the shaft sleeve, the rear side part of the bevel gear shaft extends backwards to penetrate through the rear end wall of the sliding block cavity to the outside of the supporting rod, a one-way bearing is rotationally matched at the tail end of the rear side of the bevel gear shaft, a rotating block is rotationally matched at the periphery of the one-way bearing, and the rotation of the rotating block is not influenced in the rotation process of the scale plate through the one-way rotation action of the one-way bearing.

As a further scheme of the present invention, the center block is fixed on the front end surface of the shaft sleeve, a bevel gear cavity is arranged in the center block and located at the rear side of the scale plate, the front side portion of the bevel gear shaft extends forwards into the bevel gear cavity, the bevel gear shaft and the center block are in running fit, a lead screw is in running fit with the left end wall of the bevel gear cavity, the right side portion of the lead screw extends rightwards into the bevel gear cavity, the left side portion extends leftwards out of the center block, bevel gears are fixed at the right end of the lead screw and the front end of the bevel gear shaft, and the two bevel gears are meshed with each other.

As a further scheme of the invention, the left slider is in threaded fit with the lead screw, two tooth-shaped grooves are formed in the upper end face of the scale plate, the two tooth-shaped grooves are bilaterally symmetrical around the center block, the upper ends and the outer ends of the two tooth-shaped grooves are opened, scale plate cavities penetrating the corresponding sliders are formed in the two sliders, the two scale plate cavities are in sliding fit with the scale plate, balance weight bolts are fixed on the left end face and the right end face of the scale plate, balance weight nuts are in threaded fit on the peripheries of the balance weight bolts, and the horizontal state of the scale plate when weights are not hung can be adjusted by the rotation of the balance weight nuts on the left side and the right side.

As a further scheme of the invention, the front sides of the two scale plate cavities are communicated with a pointer cavity with a forward opening, pointers are fixed on the upper end walls of the two pointer cavities, gear cavities are communicated on the upper sides of the two scale plate cavities, gear shafts are fixed between the front end walls and the rear end walls of the two gear cavities, scale plate shafts are rotatably matched in the rear end walls of the two gear cavities, the front side parts of the two scale plate shafts extend forwards to penetrate through the gear cavities on the corresponding sides to the outside of the sliding blocks on the corresponding sides, gears are fixed on the peripheries of the two scale plate shafts and the peripheries of the two gear shafts, the four gears are respectively positioned in the gear cavities on the corresponding sides, the gears on the upper side and the lower side are mutually meshed, and the two gears on the lower side are respectively meshed with the lower end walls of the gear grooves on the corresponding sides.

As a further scheme of the invention, the end of the front side of each of the two dial shafts is fixed with a dial, the lower end surfaces of the two sliding blocks are fixed with hooks, the front end surfaces of the two dials are respectively carved with scales, the front end surfaces of the two sliding blocks are respectively carved with pointers, the pointers on the left side and the right side are respectively positioned on the lower side of the dial on the corresponding side, the front end surface of the dial plate is respectively carved with two groups of scales which are bilaterally symmetrical, the slider on the right side is internally threaded with a fastening bolt, the upper part of the fastening bolt extends upwards to the outside of the slider on the right side, the fastening bolt can be abutted against the upper end surface of the dial plate, and the dial rotates one circle when the sliding block slides one unit, so that the minimum unit of the scale on the front end surface of the dial plate is subdivided.

The invention has the beneficial effects that: according to the invention, weights are hung through the hooks on the left side and the right side, when the weights are hung, the rotating angle of the scale plate is small due to the limiting effect of the limiting block, so that a demonstrator can conveniently hang the weights, the demonstrator can hang the weights without holding the scale plate by hands, after hanging the weights, the right slider can slide to any position on the right side of the scale plate, and then the bevel gear shaft is rotated, so that the left slider can gradually move leftwards until the scale plate is horizontal, thereby realizing demonstration of a lever principle, improving demonstration effect of the lever principle, and meanwhile, when the scale plate is horizontal, the limiting pin is clamped into the limiting cavity, so that the scale plate can not rotate, thereby facilitating the degree and the explanation of the demonstrator, and further subdividing the unit of the front end face of the scale plate through the dial plate, so that the test result is more accurate.

Drawings

FIG. 1 is a schematic external view of the present invention;

FIG. 2 is a schematic diagram of the overall structure of a demonstration lever for accurately reading the moment arm according to the present invention;

FIG. 3 is a schematic view of A-A of FIG. 2 in accordance with the present invention;

FIG. 4 is a schematic view of B-B of FIG. 2 according to the present invention;

FIG. 5 is a schematic view of C-C of FIG. 3 according to the present invention;

figure 6 is a schematic view of a front view of the slider component of figure 2 of the present invention.

In the figure:

10. a base; 11. a support bar; 12. hooking; 13. a counterweight nut; 14. a counterweight bolt; 15. a toothed groove; 16. a gear; 17. a center block; 18. fastening a bolt; 19. a scale plate; 20. a slider; 21. a bevel gear cavity; 22. a screw rod; 23. a bevel gear shaft; 24. a shaft sleeve; 25. pulling a rope; 26. a slider; 27. a spacing pin; 28. a one-way bearing; 29. rotating the block; 30. a pin cavity; 31. a pin; 32. a pin sliding cavity; 33. a pin spring; 34. a return spring; 35. a slider cavity; 36. a sleeve cavity; 37. a bevel gear; 38. a dial shaft; 39. a gear shaft; 40. a pointer chamber; 41. a pointer; 42. a gear cavity; 43. a dial scale; 44. a limit pin spring; 45. an arcuate cavity; 46. a limiting block; 47. a limiting cavity; 48. a limit pin sliding cavity; 49. a scale plate cavity.

Detailed Description

For purposes of making the objects and advantages of the present invention more apparent and the following detailed description of the invention, taken in conjunction with the examples, it is to be understood that the following text is intended merely to describe one or more specific embodiments of the invention, and is not intended to limit the scope of the invention as specifically claimed, and that the terms up, down, left and right, as used herein, are not limited to the exact geometric definition thereof, but include tolerances which are reasonable and inconsistent with machining or human error, the specific features of such an accurate reading moment arm demonstrating lever being set forth in detail below:

referring to fig. 1 to 6, the demonstration lever for accurately reading a force arm according to the embodiment of the invention comprises a base 10, wherein a support rod 11 is fixed on the upper end surface of the base 10, a limiting component for limiting the lever is arranged in the support rod 11, a central block 17 is arranged on the front side of the support rod 11, a scale plate 19 is fixed in the central block 17, two sliding blocks 20 are arranged on the periphery of the scale plate 19, and the two sliding blocks 20 are arranged in a left-right symmetrical manner by taking the central block 17 as the center;

spacing subassembly including set up in axle sleeve 24 in the bracing piece 11, running fit has sliding block 26 in the axle sleeve 24 periphery, be provided with spacer pin 27 in the sliding block 26, spacer pin 27 is located axle sleeve 24 upside, be equipped with the ascending spacing chamber 47 of opening in the axle sleeve 24, axle sleeve 24 downside is fixed with stopper 46, be provided with pin 31 in the sliding block 26, pin 31 is located stopper 46 downside.

As a further aspect of the present invention, a sliding block cavity 35 is disposed in the support rod 11, the sliding block 26 is in sliding fit with the sliding block cavity 35, a limit pin sliding cavity 48 with a downward opening is disposed in the sliding block 26, the limit pin sliding cavity 48 is located on the upper side of the shaft sleeve 24, the limit pin 27 is in sliding fit with the limit pin sliding cavity 48, a limit pin spring 44 is fixed between the upper end surface of the limit pin 27 and the upper end wall of the limit pin sliding cavity 48, the limit pin sliding cavity 48 is in communication with the limit cavity 47, when the limit cavity 47 is located on the lower side of the limit pin sliding cavity 48, the limit pin 27 can be inserted into the limit cavity 47, and the scale plate 19 cannot rotate any more when the scale plate 19 is horizontal due to the limiting effect of the limit pin 27, so as to facilitate the degree test.

As a further scheme of the present invention, an arc-shaped cavity 45 is provided outside the shaft sleeve 24, the limiting block 46 is in sliding fit with the arc-shaped cavity 45, a return spring 34 is fixed between the sliding block 26 and the lower end wall of the sliding block cavity 35, a pin sliding cavity 32 with a backward opening is arranged in the sliding block 26, a pin cavity 30 is communicated and arranged at the rear side of the sliding block cavity 35, the pin 31 is in sliding fit with the pin sliding cavity 32, when the pin chamber 30 is located at the rear side of the pin sliding chamber 32, the pin 31 can be inserted into the pin chamber 30, a pin spring 33 is fixed between the pin 31 and the bottom wall of the pin sliding cavity 32, a pull rope 25 is fixed between the front end face of the pin 31 and the upper end face of the limit pin 27, and the limit pin 27 can move up and down by utilizing the left-right movement of the pin 31 and the pulling of the pull rope 25.

As a further aspect of the present invention, a sleeve cavity 36 with a forward opening is communicated with the front side of the sliding block cavity 35, the front side portion of the sleeve 24 extends forward and penetrates through the sleeve cavity 36 to the outside of the support rod 11, a bevel gear shaft 23 is rotatably fitted in the sleeve 24, the rear side portion of the bevel gear shaft 23 extends backward and penetrates through the rear end wall of the sliding block cavity 35 to the outside of the support rod 11, a one-way bearing 28 is rotatably fitted on the rear end of the bevel gear shaft 23, the one-way bearing 28 can only rotate in one direction, a rotating block 29 is rotatably fitted on the outer periphery of the one-way bearing 28, and by the one-way rotating action of the one-way bearing 28, it is possible to realize that the rotation of the rotating block 29 is not affected in the rotating process of the scale plate 19.

As a further scheme of the present invention, the center block 17 is fixed on the front end surface of the shaft sleeve 24, a bevel gear cavity 21 located at the rear side of the scale plate 19 is arranged in the center block 17, the front side portion of the bevel gear shaft 23 extends forward into the bevel gear cavity 21, the bevel gear shaft 23 is in running fit with the center block 17, a lead screw 22 is in running fit with the left end wall of the bevel gear cavity 21, the right side portion of the lead screw 22 extends rightward into the bevel gear cavity 21, the left side portion extends leftward out of the center block 17, bevel gears 37 are fixed at the right end of the lead screw 22 and the front end of the bevel gear shaft 23, and the two bevel gears 37 are engaged with each other.

As a further aspect of the present invention, the left slider 20 is in threaded fit with the lead screw 22, two tooth-shaped grooves 15 are formed in the upper end surface of the scale plate 19, the lower end walls of the two tooth-shaped grooves 15 are respectively provided with a tooth shape, the two tooth-shaped grooves 15 are symmetrical left and right around the center block 17, the upper ends and the outer ends of the two tooth-shaped grooves 15 are both provided with openings, scale plate cavities 49 which penetrate the corresponding sliders 20 left and right are formed in the two sliders 20, the two scale plate cavities 49 are both in sliding fit with the scale plate 19, the left and right end surfaces of the scale plate 19 are both fixed with counterweight bolts 14, counterweight nuts 13 are in threaded fit on the peripheries of the counterweight bolts 14, and the horizontal state of the scale plate 19 when weights are not suspended can be adjusted by the rotation of the counterweight nuts 13 on the left and right sides.

As a further scheme of the present invention, the front sides of the two scale plate cavities 49 are both communicated with a pointer cavity 40 with a forward opening, the upper end walls of the two pointer cavities 40 are both fixed with pointers 41, the upper sides of the two scale plate cavities 49 are both communicated with a gear cavity 42, a gear shaft 39 is fixed between the front end wall and the rear end wall of the two gear cavities 42, the rear end walls of the two gear cavities 42 are both rotatably fitted with scale plate shafts 38, the front side parts of the two scale plate shafts 38 are both extended forward to penetrate through the gear cavities 42 on the corresponding sides to the outside of the sliders 20 on the corresponding sides, gears 16 are fixed on the peripheries of the two scale plate shafts 38 and the peripheries of the two gear shafts 39, the four gears 16 are respectively located in the gear cavities 42 on the corresponding sides, the gears 16 on the upper side and the lower side are mutually engaged, and the two gears 16 on the lower side are respectively engaged with the lower end walls of the gear grooves 15 on the corresponding sides.

As a further scheme of the present invention, the end of the front side of each of the two dial shafts 38 is fixed with a dial 43, the lower end face of each of the two sliders 20 is fixed with a hook 12, the front end face of each of the two dials 43 is marked with scales, the front end face of each of the two sliders 20 is marked with pointers, the pointers on the left and right sides are respectively located at the lower side of the corresponding dial 43, the front end face of the dial plate 19 is marked with two sets of bilaterally symmetrical scales, the slider 20 on the right side is internally threaded with a fastening bolt 18, the upper side portion of the fastening bolt 18 extends upwards to the outside of the slider 20 on the right side, the fastening bolt 18 can abut against the upper end face of the dial plate 19, and when the slider 20 slides by one unit, the dial 43 rotates by one turn, so as to subdivide the minimum unit of the scale on the front end face of the dial plate 19.

The invention discloses a demonstration lever for accurately reading a force arm, which comprises the following working procedures:

when the invention is in an initial state, the return spring 34 is in a relaxed state, the upper end surface of the sliding block 26 is abutted against the upper end wall of the sliding block cavity 35, the right end of the pin 31 is clamped in the pin cavity 30, the pin spring 33 is in a compressed state, the elastic force of the pin spring 33 is greater than that of the limit pin spring 44, the limit pin spring 44 is in a compressed state, the pull rope 25 is in a tightened state, and the limit pin 27 is positioned in the limit pin sliding cavity 48.

Hang the weight with on the couple 12 on right side, rotate fastening bolt 18 for fastening bolt 18 lower extreme breaks away from the butt with scale plate 19, moves slider 20 on right side to optional position right, reverses fastening bolt 18 again, makes fastening bolt 18 lower extreme and the up end butt of scale plate 19, makes slider 20 on right side can't freely slide.

In this process, scale plate 19 uses bevel gear axle 23 to rotate as the center for 19 left sides of scale plate are higher than the 19 right sides of scale plate, and scale plate 19 rotates, makes axle sleeve 24 rotate, thereby drives stopper 46 and uses bevel gear axle 23 to rotate as the center, because the limiting displacement in arc chamber 45, when stopper 46 rotates to 45 left end walls butt with the arc chamber, scale plate 19 can't continue to rotate, thereby makes the convenient hanging weight on left couple 12 of time delay personnel.

Because the weight has hung on couple 12 for sliding block 26 downstream under the action of gravity of weight, thereby make pin 31 impressed in pin sliding chamber 32, make stay cord 25 relax, and then make spacer pin 27 downstream under the spring action of spacer pin spring 44, because spacing chamber 47 rotates to spacer pin sliding chamber 48 right side along with axle sleeve 24 this moment, make spacer pin 27 can't block in spacing chamber 47, spacing chamber 47 lower extreme and axle sleeve 24 periphery butt.

Weights of different weights are now suspended from the left hook 12.

Then, the rotating block 29 is rotated counterclockwise (in the direction of fig. 1), and the bevel gear shaft 23 is driven to rotate by the action of the one-way bearing 28, so that the front bevel gear 37 rotates, and the left bevel gear 37 is driven to rotate, so that the screw rod 22 rotates, and the left slider 20 is driven to move leftward.

In the process, the force arm of the left slide block 20 is increased, so that the slide blocks 20 on the left side and the right side gradually tend to be balanced, and the scale plate 19 is gradually leveled.

When the sliders 20 on the left side and the right side are in a balanced state, the scale plate 19 is in a horizontal state, and the limiting cavity 47 is located under the limiting pin sliding cavity 48 at the moment, so that the limiting pin 27 moves downwards to the limiting cavity 47 under the elastic action of the limiting pin spring 44, the shaft sleeve 24 cannot rotate, the scale plate 19 cannot rotate, and subsequent reading is facilitated.

During the movement of the slider 20, the gear 16 on the lower side rotates to drive the gear 16 on the upper side to rotate, so that the dial shaft 38 on the upper side rotates, and the dial 43 rotates, and when the slider 20 moves one time, the dial 43 rotates one time.

During the degree, the scale indicated by the observation pointer 41 and the scale on the dial 43 indicated by the pointer on the front end face of the sliding block 20 are the force arm of the sliding block 20, so that the force arm reading precision is improved, and the test accuracy is also improved.

After the experiment is finished, the weight is taken down, the sliding block 26 moves upwards to the initial position under the action of the elastic force of the return spring 34, the pin 31 is clamped in the pin cavity 30 again, the limit pin 27 is pulled through the pull rope 25, the limit pin 27 moves upwards to the limit pin sliding cavity 48, the shaft sleeve 24 can freely rotate again, and the initial state is recovered.

It will be apparent to those skilled in the art that various modifications may be made to the above embodiments without departing from the general spirit and concept of the invention. All falling within the scope of protection of the present invention. The protection scheme of the invention is subject to the appended claims.

Claims

1. Demonstration lever for accurately reading a moment arm, comprising a base (10), characterized in that: a supporting rod (11) is fixed on the upper end face of the base (10), a limiting assembly used for lever limiting is arranged in the supporting rod (11), a central block (17) is arranged on the front side of the supporting rod (11), a scale plate (19) is fixed in the central block (17), two sliding blocks (20) are arranged on the periphery of the scale plate (19), and the two sliding blocks (20) are arranged in a bilateral symmetry mode by taking the central block (17) as the center;

spacing subassembly including set up in axle sleeve (24) in bracing piece (11), normal running fit has sliding block (26) in axle sleeve (24) periphery, be provided with spacer pin (27) in sliding block (26), spacer pin (27) are located axle sleeve (24) upside, be equipped with spacing chamber (47) that open side up in axle sleeve (24), axle sleeve (24) downside is fixed with spacing piece (46), be provided with pin (31) in sliding block (26), pin (31) are located spacing piece (46) downside.

2. A demonstration lever for accurate reading of moment arms according to claim 1 wherein: be equipped with sliding block chamber (35) in bracing piece (11), sliding block (26) with sliding block chamber (35) sliding fit, be equipped with spacing pin sliding chamber (48) that open side down in sliding block (26), spacing pin sliding chamber (48) are located axle sleeve (24) upside, spacing pin (27) with sliding fit between spacing pin sliding chamber (48), spacing pin (27) up end with be fixed with spacing pin spring (44) between spacing pin sliding chamber (48) the upper end wall, spacing pin sliding chamber (48) with can communicate between spacing chamber (47), work as spacing chamber (47) are located during spacing pin sliding chamber (48) downside, spacing pin (27) can insert in spacing chamber (47).

3. A demonstration lever for accurate reading of moment arms according to claim 2 wherein: an arc-shaped cavity (45) is arranged on the outer side of the shaft sleeve (24), the limiting block (46) is in sliding fit with the arc-shaped cavity (45), a return spring (34) is fixed between the sliding block (26) and the lower end wall of the sliding block cavity (35), a pin sliding cavity (32) with a backward opening is arranged in the sliding block (26), a pin cavity (30) is communicated and arranged at the rear side of the sliding block cavity (35), the pin (31) is in sliding fit with the pin sliding cavity (32), when the pin cavity (30) is located at the rear side of the pin sliding cavity (32), the pin (31) can be inserted into the pin cavity (30), a pin spring (33) is fixed between the pin (31) and the bottom wall of the pin sliding cavity (32), a pull rope (25) is fixed between the front end face of the pin (31) and the upper end face of the limit pin (27).

4. A demonstration lever for accurate reading of moment arms according to claim 2 wherein: sliding block chamber (35) front side intercommunication is equipped with forward axle sleeve chamber (36) of opening, axle sleeve (24) front side part extends forward and runs through axle sleeve chamber (36) extremely outside bracing piece (11), axle sleeve (24) normal running fit has bevel gear axle (23), bevel gear axle (23) rear side part extends backward and runs through sliding block chamber (35) rear end wall extremely outside bracing piece (11), the running fit has one-way bearing (28) on the terminal of bevel gear axle (23) rear side, running fit has rotor block (29) on one-way bearing (28) periphery.

5. A demonstration lever for accurate reading of moment arms according to claim 4 wherein: the center block (17) is fixed on the front end face of the shaft sleeve (24), a bevel gear cavity (21) located on the rear side of the scale plate (19) is arranged in the center block (17), the front side portion of the bevel gear shaft (23) extends forwards into the bevel gear cavity (21), the bevel gear shaft (23) is in running fit with the center block (17), a lead screw (22) is in running fit with the left end wall of the bevel gear cavity (21), the right side portion of the lead screw (22) extends rightwards into the bevel gear cavity (21), the left side portion extends leftwards out of the center block (17), bevel gears (37) are fixed at the tail ends of the right side of the lead screw (22) and the front side of the bevel gear shaft (23), and the two bevel gears (37) are meshed with each other.

6. A demonstration lever for accurate reading of moment arm according to claim 5 wherein: left slider (20) with lead screw (22) screw-thread fit, be equipped with two tooth shape grooves (15), two in scale plate (19) upper end face tooth shape groove (15) with center block (17) are central bilateral symmetry, two equal opening setting in tooth shape groove (15) upper end and the outer end, two it runs through the corresponding side all to be equipped with about in slider (20) scale plate chamber (49) of slider (20), two scale plate chamber (49) all with scale plate (19) sliding fit, the terminal surface all is fixed with counter weight bolt (14) about scale plate (19), equal screw-thread fit has counter weight nut (13) in counter weight bolt (14) periphery.

7. A demonstration lever for accurate reading of moment arm according to claim 6 wherein: the front sides of the two scale plate cavities (49) are respectively communicated with a pointer cavity (40) with a forward opening, pointers (41) are fixed on the upper end walls of the two pointer cavities (40), gear cavities (42) are respectively communicated with the upper sides of the two scale plate cavities (49), gear shafts (39) are fixed between the front end walls and the rear end walls of the two gear cavities (42), scale plate shafts (38) are respectively and rotatably matched in the rear end walls of the two gear cavities (42), the front side parts of the two scale plate shafts (38) respectively extend forwards to penetrate through the gear cavities (42) on the corresponding sides to the outside of the sliding blocks (20) on the corresponding sides, gears (16) are fixed on the peripheries of the two scale plate shafts (38) and the peripheries of the two gear shafts (39), the four gears (16) are respectively positioned in the gear cavities (42) on the corresponding sides, and the gears (16) on the upper side and the lower side are mutually meshed, the two gears (16) on the lower side are respectively meshed with the lower end walls of the tooth-shaped grooves (15) on the corresponding sides.

8. A demonstration lever for accurate reading of moment arms according to claim 7 wherein: two scale disc axle (38) front end all is fixed with calibrated scale (43), two the terminal surface all is fixed with couple (12) under slider (20), two calibrated scale (43) front end face all is carved with the scale, two the pointer has all been carved with to slider (20) front end face, and the pointer of the left and right sides is located respectively corresponding the side calibrated scale (43) downside, the terminal surface all is carved with two sets of bilateral symmetry's scale before scale plate (19), the right side slider (20) interior screw-thread fit has fastening bolt (18), fastening bolt (18) upside part upwards extends to the right side outside slider (20), fastening bolt (18) can with scale plate (19) up end butt.