RU2473132C1 - Device for demonstrating properties of elastic waves - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: posts are mounted on a base and are attached to a horizontal rod. Two bushings are placed on the rod with possibility of movement and rigid fixation thereon. A helical spring is suspended on threads of equal length. An additional spring, which is more rigid than the helical spring, is worn onto the rod and placed between the bushings. Top ends of the threads of equal length are tied to coils of the additional spring. The rod has a longitudinal groove in its lower part.

EFFECT: simple design and reduced labour input in manufacturing.

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Description

The invention relates to demonstration devices that reveal the physical properties of elastic waves, and can be used in the educational process, for example, when giving lectures or in a laboratory workshop.

A device for generating a traveling wave [1] is known, including a base with racks installed on it, to which a rod is attached, oriented horizontally, on which spherical weights located between elastic spring coils are suspended using equal lengths, damping elements are attached to some weights, in liquid.

With mechanical excitation of the end of the spring, a longitudinal traveling wave is excited in it, which clearly demonstrates the physical processes that occur during the propagation of elastic longitudinal waves in solid media.

The disadvantage of this device is the design complexity, as well as limited demonstration capabilities, consisting in the impossibility of excitation of transverse waves "weights-springs" in the structure, the rigid attachment of the threads to the rod, does not allow changing the inter-turn pitch of the springs and, ultimately, the phase velocity of the longitudinal waves.

Signs that coincide with the declared object: base, racks, rod, oriented horizontally, threads of equal length.

A device for demonstrating longitudinal waves is also known, comprising a base with uprights mounted on it, to which two rods are attached, oriented horizontally and parallel to each other; a spiral spring is suspended from the rods using threads of equal length [2, 3].

With mechanical excitation of the end of the spring, a longitudinal wave propagates along it, which clearly demonstrates the physical processes that occur during the propagation of elastic longitudinal waves in solid media.

The disadvantage of this device is the limited demonstration capabilities, consisting in the impossibility of excitation of transverse waves in the spring due to the bifilar suspension of the coil of the spring by threads in a plane perpendicular to the axis of the spring, creating only one degree of freedom when moving the coil of the spring, and the rigid attachment of the threads to the rods, which does not allow change the interturn pitch of the spring and, ultimately, the phase velocity of the longitudinal waves.

Signs that coincide with the declared object: base, uprights, rod oriented horizontally, threads of equal length, spiral spring.

It is also known a device for demonstrating waves in a spring [4], comprising a base with struts mounted on it, to which a rod is attached, oriented horizontally, on the rod there are bushings that move freely along the rod, and a spiral spring is suspended from the bushings with threads of equal length.

With mechanical excitation of the end of the spring, a longitudinal or transverse wave can propagate along it, which clearly demonstrates the physical processes that occur during the propagation of elastic longitudinal and transverse waves in solid media.

The reasons that impede the achievement of the technical result are limited demonstration capabilities, due to the fact that during the operation of the known device there is an arbitrary and unregulated arrangement of the bushings along the rod, which does not allow to demonstrate, for example, the dependence of the phase velocity of the wave on the linear density of the coil of the spring, and also unstable picture of wave motion, especially when demonstrating longitudinal standing waves.

Signs that coincide with the declared object: base, struts, rod oriented horizontally, two bushings, threads of equal length, coil spring.

In the device for demonstrating elastic waves [5], having the greatest number of matching features with the claimed device, it is possible to uniformly change the inter-turn distance in the spring and, accordingly, the phase velocity of the longitudinal waves. It contains a base on which racks are mounted with a horizontally oriented rod attached to them. On the rod are bushings that can freely move along it. A spiral spring is suspended from the bushings using threads of equal length, and a multi-link parallelogram articulated multi-link is attached to the bushings by middle hinges. In this device, the uniform inter-turn step is set by the solution of the articulated multi-link parallelogram, which also allows changing the inter-turn step of the spring within the necessary limits.

The reasons that impede the achievement of the technical result are the complexity of the design and the complexity of manufacturing an articulated multi-link parallelogram.

Signs that match the declared object: base, racks with a horizontally oriented rod attached to them, threads of equal length and a coil spring.

The objective of the invention is to simplify the design of the device, reducing the complexity of its manufacture.

The technical result is achieved by the fact that in a known device for demonstrating the properties of elastic waves, containing a base with racks installed on it, to which a rod is attached, oriented horizontally, two bushings located on the rod with the possibility of movement and rigid fixation on it, and threads of equal length on which the coil spring is suspended, according to the invention, an additional spring is inserted, put on a rod located between the bushings and having a stiffness greater than the stiffness of the coil spring, etc. This additional spring coils to attached the upper ends of strands of equal length, and the rod in its lower part has a longitudinal groove.

This allows us to simplify the design of the device, reduce costs in its manufacture while maintaining its demonstration capabilities.

The invention is illustrated by drawings.

Figure 1 shows the device device for demonstrating the properties of elastic waves, and figure 2 is one of the possible cross-section of the rod with an additional spring on it.

The device (figure 1) consists of a base 1 with racks 2 and 3 installed on it, to which a rod 4 is attached, oriented horizontally and having a longitudinal groove in its lower part, two bushings 5 and 6 are freely located on the rod, freely moving along the rod 4 and having the possibility of their rigid fixation, between the bushings 5 and 6 on the shaft 4 there is an additional spring 7 in a compressed state, to which a spiral spring 9 is suspended using threads of equal length 8, and the additional spring 7 has a stiffness significantly greater, than the stiffness of the coil spring 9 (at least 3 times or more). So that the fastening elements of the upper ends of the threads of equal length 8 do not interfere with the free movement of the turns of the additional spring 7 along the rod 4, a longitudinal groove and a recess are made in its lower part, as shown in FIG. 2. This design allows using an additional spring 7 to establish a given uniform inter-turn pitch of the spiral spring 9 and to maintain it constant during the demonstrations.

The device operates as follows. In the initial state, the spring 9 is in equilibrium with the inter-turn step, which is set by the length of the additional spring 7. To excite the transverse wave with the help of a vibrator or hand, vibrations of the extreme turns of the spring 9 are created in a plane perpendicular to its axis. Due to the presence of elastic forces and inertia (see M. M. Arkhangelsky. Physics. Mechanics, Moscow: Prosveshchenie, 1965, p. 358), transverse vibrations propagate along spring 9 at a certain speed. If the exciting bias is stopped, then we get a shear pulse propagating along the spring, and when two, three periods of exciting vibrations are made, a wave train arises corresponding to the form of the harmonic function. Creating continuous oscillations during the time necessary for the wave to propagate to the end of spring 9, we observe the continuous filling of the field of spring 9 with a traveling wave at a certain constant speed, and then the formation of a standing wave.

With mechanical action on the spring 9 along its axis, we obtain in the spring a longitudinal wave propagating with the speed of a longitudinal wave. The deformation of the additional spring 7 will be negligible and can be neglected during the experiment.

Experiments with elastic traveling longitudinal and transverse waves convincingly and clearly show that the values of speed, for example, a longitudinal wave, a longitudinal train and a longitudinal impulse, have the same value. Further, it is experimentally demonstrated that the wave velocity does not depend on the amplitude and frequency. Changing the frequency of the oscillations, we observe an inversely proportional relationship between the frequency and wavelength. In the field of elastic deformations of the spring 9, Hooke's law is satisfied, and its stiffness coefficient will remain constant when creating a wave motion. Changing the inter-turn pitch within the dimensions of the device ensures the constancy of the spring stiffness coefficient.

To demonstrate that the wave velocity depends on the elastic properties of the spring 9, springs 9 with different stiffnesses are used. According to the theory of elastic waves (see Crawford F. Waves. M .: Nauka, 1984, p. 85) the phase velocity of the wave υ depends not only on the stiffness coefficient K of the coil of the spring, but also on the linear density of the spring ρ, which depends on its mass m and inter-turn pitch of the spring a according to the formula

Thus, the wave velocity for the same spring 9 depends linearly on its inter-turn step. The experiments on the device showed that such a relationship is true. The demonstration of this causal relationship is carried out by changing the distance between the sleeves 5 and 6, and this leads, respectively, to a change in the inter-turn pitch along the entire length of the spring 9. The wave velocity is determined by the time of its propagation along the length of the spring or by measuring the length of the standing wave with a known oscillation frequency.

Thus, the introduction of an additional spring 7 allows you to simplify the design of the device, reduce its cost, while creating a uniform change in the inter-turn pitch of the spring 9.

The practical implementation of the device is not difficult. The model of this device is made and successfully operated when reading the relevant sections of the physics training course.

Information sources

1. Patent JP 59226377 "Progressive wave generator", IPC G09B 23/06, publ. 08/29/1988.

2. Lecture demonstrations in physics. / Ed. V.I. Iveronova, Moscow: Nauka, 1972, p.206-207.

3. Leon M. Reynolds, “Folding slinky wave demonstrator”, The physics teacher, v.16, No. 9, 1978, p.652-654. USA

4. John F Spivey, “Versatile mount for slinky wave demonstrator”, The physics teacher, v.20, No. 1, 1982, p. 52. USA

5. Patent RU2421821, IPC G09B 23/06, publ. 06/20/2011.

6. Patent GB 1445290, "Apparatus vor demonstrating wave motion" IPC G09B 23/06, publ. 08/11/1976.

7. Patent JP 59204080, “Wave motion experiment apparatus” IPC G09B 23/06, publ. 11/19/1984.

8. Patent JP 61046972 "Longitudinal wave demonstration apparatus", IPC G09B 23/06, publ. 03/03/1986.

9. Patent SU 875442 "Training device for demonstrating a traveling wave" IPC G09B 23/06, publ. 10/23/1981.

10. Patent SU918965 "Training device for demonstrating a traveling wave" IPC G09B 23/06, publ. 04/07/1982.

11. Patent SU 1485290 "Training device in physics for the demonstration of wave processes" IPC G09B 23/06, publ. 09/30/1887.

12. Patent SU 1529273 "Educational device in physics" IPC G09B 23/06, publ. 12/15/1989.

13. Patent US 3518780 "Longitudinal wave propagation demonstrators", IPC G09B 23/06, publ. 07/07/1970.

14. Patent US 5975911 "Mechanical oscilloscope" IPC G09B 23/06, publ. 2.11 1999.

Claims (1)

A device for demonstrating the properties of elastic waves, comprising a base with racks mounted on it, to which a rod is attached, oriented horizontally, two bushings located on the rod with the possibility of movement and rigid fixation on it, and threads of equal length on which a coil spring is suspended, characterized by the fact that an additional spring is inserted into it, put on a rod located between the bushings and having a stiffness greater than the stiffness of the coil spring, while attaching to the turns of the additional spring s upper ends of strands of equal length, and the rod in its lower part has a longitudinal groove.

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