This experiment examines how the sound propagation of a mechanical egg timer behaves under normal pressure compared to an evacuated desiccator. The egg timer is triggered in both environments, and the perceived loudness as well as possible sound alterations are analyzed. This investigation provides insights into the acoustic properties of gases and their significance for sound propagation.

Null Hypothesis: he sound intensity and propagation of the mechanical egg timer are identical under normal pressure and in an evacuated desiccator.

1. Introduction

Sound is a mechanical wave1[Sound waves are pressure fluctuations in a medium that propagate as longitudinal waves] that requires a medium for propagation. This study examines the dependency of sound propagation on air density by triggering a mechanical egg timer in a normal pressure and an evacuated system. The results aim to contribute to a better understanding of the importance of gases as a transmission medium for sound.

2. Material and Methods

Material:

  • Mechanical egg timer
  • Desiccator2[A desiccator is an airtight container used for drying and storing samples in a dry environment] with vacuum pump [A vacuum pump is a device that removes gases from a closed system to create a low-pressure environment]
  • Sound level meter3[A sound level meter is a device used to measure the loudness of sound in decibels (dB)]
  • Manometer4[A manometer is a device for measuring pressure in gases or liquids] for pressure monitoring

Experimental Procedure:

  1. The mechanical egg timer is placed outside the desiccator on a sound-reflecting surface and triggered.
  2. The loudness of the egg timer is recorded with the sound level meter at a constant distance.
  3. The egg timer is then placed inside the desiccator.
  4. The desiccator is evacuated with the vacuum pump until a near-vacuum state is achieved.
  5. The egg timer is triggered again inside the evacuated desiccator.
  6. The loudness is measured under the same conditions.
Fig 1.: Mechanical egg timer

Procurement:

3. Results

After triggering the egg timer under normal pressure, a distinct ticking and ringing sound was perceptible. The measured sound level was approximately 60 dB at a distance of 20 cm. In the evacuated desiccator, however, no acoustic signal was perceptible. The sound level meter showed only minimal fluctuations, within the range of background noise.

4. Discussion

The results confirm the physical necessity of a medium for sound propagation. Under normal pressure, the generated sound is transmitted by air molecules, making it audible. However, in the evacuated desiccator, air molecules are largely absent, so the mechanical vibrations of the egg timer are not or only significantly reduced in their transmission to the environment. This corresponds to the physical principle that sound waves are longitudinal pressure waves5[Longitudinal pressure waves are waves in which the particle motion is parallel to the wave propagation direction], requiring a material interaction.

Sound waves arise from mechanical oscillations6[Mechanical oscillations are periodic movements of a body around an equilibrium position] of a sound source, causing periodic pressure changes in the surrounding medium. These pressure changes propagate through compressions and rarefactions of particles. The speed at which sound propagates depends on the physical properties of the medium and follows the equation:

c=sqrt{E/rho}

where c is the speed of sound7[The speed of sound is the velocity at which sound waves propagate through a medium], E is the elastic modulus8[The elastic modulus is a material constant that indicates how a material reacts to mechanical stress], and ho is the density9[Density is the mass of a substance per unit volume] of the medium. Since the density of air is greatly reduced in the desiccator, the ability of the medium to transport sound also decreases.

The sound intensity I is proportional to the square of the sound pressure :

I proportional p^2

Since the sound pressure approaches zero in the nearly airless space of the desiccator, the intensity also decreases drastically, making the sound no longer audible. The absence of a transmission medium explains why the mechanical vibrations of the egg timer do not produce audible sounds outside the desiccator.

Another important concept is acoustic impedance Z, defined as:

Z = rho*c

Since the density in the desiccator is nearly zero, the sound is almost completely reflected at the walls of the desiccator instead of propagating within the vessel. This also means that no indirect transmission of sound can occur.

This study impressively demonstrates why no sound propagation is possible in space, where near-perfect vacuum conditions exist. This means that without a medium, no mechanical wave can be transmitted from one point to another, which scientifically supports the well-known phrase, “In space, no one can hear you scream.”

Safety

  • The desiccator must be vacuum-resistant to prevent implosion.
  • Additionally, the pump should not be overloaded to avoid mechanical damage.
  • It is recommended to wear safety goggles and conduct the experiment in a stable environment.



  • 1
    [Sound waves are pressure fluctuations in a medium that propagate as longitudinal waves]
  • 2
    [A desiccator is an airtight container used for drying and storing samples in a dry environment]
  • 3
    [A sound level meter is a device used to measure the loudness of sound in decibels (dB)]
  • 4
    [A manometer is a device for measuring pressure in gases or liquids]
  • 5
    [Longitudinal pressure waves are waves in which the particle motion is parallel to the wave propagation direction]
  • 6
    [Mechanical oscillations are periodic movements of a body around an equilibrium position]
  • 7
    [The speed of sound is the velocity at which sound waves propagate through a medium]
  • 8
    [The elastic modulus is a material constant that indicates how a material reacts to mechanical stress]
  • 9
    [Density is the mass of a substance per unit volume]