12 Jan, 2013
PRESENTATION: A pair of tuning forks is assembled on resonance boxes with an open front, so the sound intensity is magnified and the frequency of the emitted sound decreased. By placing small adjustable masses at their ends the frequency is raised when they move towards the base.
- Frequency measurement with a chromatic tuner, H. David Sheets, Phys. Teach. 31, 504 (1993)
- Inexpensive Instruments for a Sound Unit, B. Brazzle, Phys. Teach. 49, 228 (2011)
INTRODUCTION: The tuning fork is an object that produces sound waves, because when its fork prongs shaped in U are struck against something or with something they start vibrating, stirring the molecules of the surrounding air, although the human eye cannot detect any movement. As an amplifying element is necessary, the non-vibrating part must rest on the resonance box. It is usually employed as a musical tuner. In each video we can watch a brief explanation of the experiment dealt with here.
OBJECTIVE: To listen to the wave transmission between 2 tuning forks and watch their vibration when struck and when receiving the wave.
MATERIALS: 2 tuning forks, 2 resonance boxes, 2 forks, drumstick, ping-pong ball, water glass, cord, support.
SET UP: The tuning forks are introduced in the wooden boxes supports and they are struck against the drumstick. In the experiment with the ball, we tie the ball with some cord that is tied to a door handle in such a way that the ball is slightly in contact with the tuning fork.
- Choosing a frequency at random but identical for both tuning forks, the same wave transmission is kept.
- On the other hand, if the frequencies we choose are different for each one, those waves are not transmitted.
- To show heterodyne interference we have oriented the opening of the boxes that support the tuning forks in a converging direction and each tuning fork with a different frequency. When we strike each of them, we check a pulse wave.
CONCEPTS: tuning fork, resonance, waves, hertzs, vibration, heterodyne interference.
- Tipler P.A. Física. Barcelona: Reverté, 2010.
- De Juana J.M., Física General, Pearson, 2009.
- Serway R.A y J.W.Jewett. Física, Thomson-Paraninfo, 2010.
STUDENTS 2012-2013: Andrea Mouriño, Rodrigo Novoa, Victor Pérez
LINK pdf STUDENTS (in Spanish):