Measuring longitudinal wave speed in solids: two methods and a half

Abstract

Three methods to analyse longitudinal wave propagation in metallic rods are discussed. Two of these methods also prove to be useful for measuring the sound propagation speed. The experimental results, as well as some interpretative models built in the context of a workshop on mechanical waves at the Graduate School for Pre-Service Physics Teacher Education, Palermo University, are described. Some considerations about observed modifications in trainee teachers' attitudes to utilizing physics experiments to build pedagogical activities are discussed.

A problem-based approach to elastic wave propagation: the role of constraints

“…A typical signal detected by the experimental apparatus is reported in the appendix, where estimates of the mechanical wave pulse speed in brass and aluminium, found by using τ values measured with different length rods, are reported. More details can be found in [5].…”

“…So, a reflection and a transmission of the incoming wave pulse are to be expected at the vice position. It is well known that rod particle velocity, due to the wave pulse reflected at a boundary between two materials, is related to the characteristic impedance, Z = ρc, of materials on both sides of the boundary [5,9], where ρ is the rod's density and c is the speed of the wave pulse. If u i indicates the particle velocity due to the incident wave pulse and u r the particle velocity due to the reflected pulse, we have…”

“…In a previous paper [5], we discussed different methods for measuring sound speed in metals. These methods are mainly based on the generation of wave pulses in metallic rods by means of collisions of a metallic body at one of the rods' ends and on the measurement of the time the waves take to travel along the rods.…”

Measurement of elastic modulus and ultrasonic wave velocity by piezoelectric resonator

“…Longitudinal travelling acoustic waves ranged used in [5] for wave velocity measurement. Time of flight was detected by sound sensor or by opening an electric circuit caused by the displaced pendulum bob.…”

Collisions and Mechanical Wave Propagation in Elastic Rods

“…In a previous paper [3] we discussed different methods of measuring the speed of sound in metals. These methods are mainly based on the generation of wave pulses in a metallic rod, by means of collisions of a metallic body at one of the rod's ends, and on measurement of the time the pulses take to travel along the rod.…”