RU2421821C1 - Device for demonstrating properties of elastic waves - Google Patents

Abstract

FIELD: physics. ^ SUBSTANCE: posts to which a horizontal rod is attached are mounted into a base. There are freely moving bushings on the rod. A helical spring is suspended from the bushings by a thread of equal length. An articulated multi-link parallelogram is attached to the bushings by middle hinges. ^ EFFECT: possibility of uniformly changing the inter-turn spacing on the entire length of the spring when changing its length. ^ 1 dwg

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 arise during the propagation of elastic longitudinal waves in solid media.

The disadvantage of this device is the complexity of the design, as well as limited demonstration capabilities, which include the impossibility of excitation of transverse waves in the “weight-springs” 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, 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 disadvantages of this device are 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 match the declared object: base, racks, rod, threads of equal length, coil spring.

The prototype of the claimed device is a device for demonstrating waves in a spring [4], having the largest number of matching features and containing a base with racks installed on it, to which a rod is oriented, oriented horizontally; there are bushings on the shaft that move freely along the shaft, and a spiral spring is suspended from the bushings using threads of equal length.

With mechanical excitation of the end of the spring, a longitudinal or transverse wave can propagate through it, which clearly demonstrate the physical processes that arise 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 arises an arbitrary and unregulated arrangement of the bushings along the rod, which makes it impossible 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 match the declared object: base, racks, rod, bushings, threads of equal length, spiral spring.

The objective of the invention is the expansion of demonstration and didactic capabilities in demonstrating the properties of elastic waves.

The technical result is achieved by the fact that in the device containing the base with racks installed 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 the help of threads of equal length; an articulated multi-link parallelogram is attached, attached by middle hinges to the bushings. This allows for uniform change in the inter-turn pitch along the entire length of the coil spring when changing its length, and also to maintain constant distances between the bushings during spring deformation.

A utility model is illustrated in the drawing, which shows a device for demonstrating elastic waves. It consists of a base 1 with racks 2 mounted on it, to which a rod 3 is attached, oriented horizontally; on the rod there are bushings 4, freely moving along the rod 3, a spiral spring 8 is suspended from the bushings 4 using threads of equal length 7, and a multi-link parallelogram 6 is attached to the bushings 4 by middle hinges 5. This design gives two degrees of freedom to the spring coils and allows using the additionally introduced articulated multi-link parallelogram, smoothly and quickly set the specified inter-turn spring pitch and keep it constant during the demonstrations.

This allows you to visually show the dependence of the propagation velocity of longitudinal and transverse waves on the linear density of the spring.

The device operates as follows. In the initial state, the spring is in equilibrium with a minimally specified inter-turn step, which is set by the solution of the articulated multi-link parallelogram. To excite a transverse wave using a vibrator or hand, vibrations of the extreme turns of the spring are created in a plane perpendicular to the axis of the spring. Due to the presence of elastic forces and inertia (see MM Arkhangelsky. Physics. Mechanics. M.: Education, 1965, p. 358) transverse vibrations propagate along the spring. Moreover, if the exciting bias is stopped, returning to the initial state, then we get a shear pulse propagating along the spring, and when two, three periods of exciting vibrations occur, a wave train arises, which already has the character of a wave motion corresponding to the form of a harmonic function that propagates along the spring with some speed. By continuously creating oscillations (during the time necessary for the wave to propagate to the end of the spring, i.e., until the reflected wave is formed), we observe the continuous filling of the spring field by a traveling wave with a certain constant speed equal to the propagation velocity of both the momentum and the wave train, and then the formation of a standing wave.

With mechanical action on the spring along its axis, we obtain a longitudinal wave in the spring, propagating at a constant speed.

Experiments with elastic traveling waves, longitudinal and transverse waves convincingly and clearly show that the magnitude of the velocity, for example, a longitudinal wave, a longitudinal train and a longitudinal pulse, have the same value. Further, it is experimentally demonstrated that the wave velocity does not depend on the amplitude and frequency. However, changing the oscillation frequency, we observe an inversely proportional relationship between the frequency and wavelength, which is required to verify the dispersion relation (see Crawford F. Waves. M: Nauka, 1984, p. 83).

To demonstrate that the wave velocity depends on the elastic properties of the spring, a correct experiment is required, since the changes are not so large, and this dependence is not simple. To do this, we focus on demonstrating the dependence of the wave velocity on the stiffness of the spring. In the field of elastic deformations, Hooke's law is satisfied, and the stiffness coefficient of a given spring will remain constant when creating a wave motion. Preliminary experiments have shown that for plastic deformation of a spring, it is necessary to increase its length by more than 40 times. Therefore, changing the inter-turn pitch within the dimensions of the device ensures the constancy of the spring stiffness coefficient. However, according to the theory of elastic waves (see Crawford F. Waves. M .: Nauka, 1984, p. 85), the phase velocity of the wave v 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 the mass m and interturn pitch of spring a, by the formula

Thus, the wave velocity for the same spring depends only on the inter-turn pitch and the mass of the coil. The experiments on the device showed that such a relationship is true. The demonstration of this causal relationship is carried out by increasing the solution of the articulated multi-link parallelogram, leading to a change in the distance between the bushings and, accordingly, to a change in the inter-turn pitch along the entire length of the spring. The speed of the wave is determined by the time of its propagation along the length of the spring or by measuring the length of the standing wave at a known oscillation frequency.

Thus, the additional introduction of an articulated multi-link parallelogram allows you to create an equal inter-turn change in the spring pitch and thereby expand the didactic capabilities of the device by demonstrating the dependence of the wave velocity on the linear density of the spring turns.

The practical implementation of this device is not difficult. This device is manufactured and successfully operated while 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. M .: 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 GB 1445290 "Apparatus for demonstrating wave motion", IPC G09B 23/06, publ. 08/11/1976.

6. Patent JP 59204080 "Wave motion experiment apparatus", IPC G09B 23/06, publ. 11/19/1984.

7. Patent JP 1046972, "Longitudinal wave demonstration apparatus", IPC G09B 23/06, publ. 03/03/1986.

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

9. Patent SU 918965 "Training device for demonstrating a traveling wave", IPC G09B 23/06, publ. 04/07/1982.

10. Patent SU 1485290 “A training device in physics for demonstrating wave processes”, IPC G09B 23/06, publ. 09/30/1887.

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

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

13. Patent US 5975911 "Mechanical oscilloscope", IPC G09B 23/06, publ. November 2, 1999.

Claims (1)

A device for demonstrating the properties of elastic waves, comprising a base with struts mounted on it, to which a horizontally oriented rod is attached, bushings located on the rod with free movement along it, and a spiral spring suspended from the bushings using threads of equal length, characterized in that an additional articulated multi-link parallelogram is attached to it, attached by middle hinges to the bushings.

Images