Chladni patterns

Chladni was a German physicist and a trained musician and is best known for inventing a technique to visualize the various modes of vibration of a rigid surface.

Take a flat metal plate, fix it at any point (say at the center) and sprinkle some fine sand particles on it.

Using a violin bow, gently excite any edge of the plate to witness beautiful normal mode patterns (known as Chladni patterns/figures).

Notice that by pinching the plate at different points one gets different patterns.

                               Gif source video: Steve Mould

Inverse Chladni plates

There is much more than what meets the eye in this experiment as the patterns that emerge are dependent on the size of the particles that one chooses and the acceleration of the resonating plate.

Bigger particles ( > 0.15 micrometers ) – tend to accumulate at the nodes of the vibrating plate – Chladni figures.

Smaller particles ( e.g Lycopodium powder ) – tend to accumulate at the anti-nodes of the vibrating plate – Inverse Chladni figures.

                   Source : “Air-induced inverse Chladni patterns”

What causes them?

Although the traditional Chladni patterns are discussed extensively in the context of solid mechanics and normal modes of vibration in engineering.

But that’s NOT where the story ends.

Michael Faraday argues in his remarkable paper that the ‘inverse Chladni patterns’ that one observes are not a run of mill mechanics problem with a secondary mode of vibration.

Instead, he demonstrates that the vibrating plate induces air currents on top of it, which drags the fine particles along to the antinode. This is completely counterintuitive since one doesn’t expect the air to play such a pivotal role in these patterns.

A plot of the velocity profile above the Chladni plate.  Notice the air currents that are caused by the vibrating plate. This phenomenon is often referred to as “Rayleigh streaming”.

Thus far we have merely considered a plate vibrating in air.

But what if we were to look at water atop a vibrating plate? For that, check out the accompanying FYFD post and stay tuned for more tomorrow.

Advertisement

Using sound to put off fires

Researchers at the George Mason University are using 30-60 Hz acoustic wave signals to put off fire. This works because what sound is really a longitudinal wave traveling through space. i.e

                                                    Source

This work is quintessential beneficial because in places like the ISS fire extinguishers are not as effective as they are on earth because they spread out in all directions.

But sound waves on the other hand can be directed to quench the flame.

Have a great day!

EDIT: Thanks for enlightening me on the usage of the word ‘quintessential’

Source: physicsworld.com

The Clapperboard Resolution.

The snap of the clapperboard is hard to miss. Frequented in Musicals, Dramas, and in movies. This quotidian device serves as an important tool in the filmmaking and video production. 

I am sure that you are aware of its function – to designate and mark particular scenes and takes recorded during a production. 

But the most important function ( that is often forgotten )of a clapperboard is to assist in the synchronizing of picture and sound! How, you ask?

The sharp “clap” noise that the clapperboard makes can be identified easily on the audio track, and the shutting of the clapstick can be identified easily on the separate visual track.

The two tracks can then be precisely synchronised by matching the sound and movement

That’s a wrap!

Have a Good Day!

The Crazy- Einstein Beats Phenomenon.

When two laser beams at slightly different frequencies are combined onto a screen, the resulting interference pattern produces “beats” in time (i.e. the pattern alternates between light and dark), similar to how the sound produced by two slightly out of tune guitar strings plucked simultaneously will wobble between loud and soft. 

Why is this special?

In everyday life the beating of light waves is usually undetectable, because 

(1) most light we see is incoherent and 

(2) our eyes cannot resolve beat frequencies beyond a few tens of cycles per second. 

Since visible light waves oscillate at several hundred trillion cycles per second, finding two light sources with a relative frequency difference small enough to observe by eye is generally believed to be prohibitively difficult.

Shattering Barriers.

We get around this difficulty by building an interferometer, which splits apart a laser beam along two paths, and then shifting the frequencies of the light beam along each path by slightly different amounts. When the beams are recombined, the interference pattern they produce will wobble at a rate equal to the frequency difference between the beams. 

If you are interested, you can read about the Laser Gyroscope and the source research paper as well. 

Cheers! 

PC: acs-psu.

Source: arxiv.org

Types of Damping

Damping is an influence within or upon an oscillatory system that has the effect of reducing, restricting or preventing its oscillations.

There are 4 types of damping:(in the order of the animations shown)

1. Under Damped System.

The system oscillates (at reduced frequency compared to the undamped case) with the amplitude gradually decreasing to zero.

2. Critically Damped System.

The system returns to equilibrium as quickly as possible without oscillating.

3. Over Damped System.

The system returns to equilibrium without oscillating.

4. Un-Damped System.

The system oscillates at its natural resonant frequency

( Sources: xmdemo, timewarp,wikipedia)