Minggu, 24 Januari 2010

Mr. Alba's post

In this post, i'll gave respond to the Mr. Albaini's post at www.interzone81.blogspot.com with my summary

So wave is where the individual parts of material always move in cyclical pattern.
There's 2 waves, it is:

Transverse Wave

"the particle displacement is parallel to the direction of wave propagation"
like when we shake a rope, and light wave.

Longitudinal Wave

"the particle displacement is perpendicular to the direction of wave propagation"
It's like when we stress a slinky and in sound wave. There's some other examples that i didn't understand.

And there's a:
Wavelength, is the lenght of a wave, determined by 1 phase and then back to the same phase.
Amplitude, is the height of the wave.
Velocity, is the speed of the wave.
Frequency, number of cycles in 1 second
Period, time taken for 1 cycle << addition from me


Light is electromagnetic radiation, particularly radiation of a wavelength that is visible to the human eye.
In the past, scientists debated about light, is it wave or particle.

Light as particle
Einstein's explained by imagining photoelectric effect, which light striking a metal surface ejected electrons from the surface.

Light as a wave
Thomas Young proof that the wave is the nature of light by doing double-slit experiment.
A beam of light(laser) is shone on a pair of 2 parallel slits. Light diffracts from each slit and projected on screen. In the space after the light difracts, it overlaps and formed interference pattern(light and dark) on the screen, it's called 'fringes'.

In the double slit experiment, we determine λ with this equation

a, is the slit separation(distance between the centres of the 2 slits)
x, is the distance between the centres of 2 close bright/dark fringes
D, is the distance between slits's midpoint and central fringe on screen

To observe interference fringes with white light instead of laser, it's necessary use a single slit behind/before the double slit. it's to make a clearer fringes.
To see and doing double-slit experiment, check this site

Sabtu, 23 Januari 2010

Wave and HSW presentation

this presentation is about how people can walk accross hot embers.
many people thought it was done by magic, but in this presentation, i'll tell you how people can walk accross those hot coals based on physics. It's actually depends on poor conductor, very good insulation, short time span and some tricks.
- The ashes always covered the coals, this is make the insulation.
- The wood that burned down into lightweight carbon structure are very poor conductor.
- And by walking briskly accross the hot embers make your feet doesn't have enough time to get burn.


It'll motivate you, no success can be done by magic, but it always accomplished by sacrifice and hard work.... and after you apply to your life... you can do anything even a magic..

this is some presentation about wave, like the definition about wave from the older post, and this is the presentation


Minggu, 17 Januari 2010

Wave Article and Movie


A wave is a disturbance that propagates through space and time, usually with transference of energy. A mechanical wave is a wave that propagates or travels through a medium due to the restoring forces it produces upon deformation. There also exist waves capable of traveling through a vacuum, including electromagnetic radiation and probably gravitational radiation. Waves travel and transfer energy from one point to another, often with no permanent displacement of the particles of the medium (that is, with little or no associated mass transport); they consist instead of oscillations or vibrations around almost fixed locations.


Periodic waves are characterized by crests (highs) and troughs (lows), and may usually be categorized as either longitudinal or transverse. Transverse waves are those with vibrations perpendicular to the direction of the propagation of the wave; examples include waves on a string, and electromagnetic waves. Longitudinal waves are those with vibrations parallel to the direction of the propagation of the wave; examples include most sound waves.

When an object bobs up and down on a ripple in a pond, it experiences an orbital trajectory because ripples are not simple transverse sinusoidal waves.

Ripples on the surface of a pond are actually a combination of transverse and longitudinal waves; therefore, the points on the surface follow orbital paths.

All waves have common behavior under a number of standard situations. All waves can experience the following:

  • Reflection — change in wave direction after it strikes a reflective surface, causing the angle the wave makes with the reflective surface in relation to a normal line to the surface to equal the angle the reflected wave makes with the same normal line
  • Refraction — change in wave direction because of a change in the wave's speed from entering a new medium
  • Diffraction — bending of waves as they interact with obstacles in their path, which is more pronounced for wavelengths on the order of the diffracting object size
  • Interferencesuperposition of two waves that come into contact with each other (collide)
  • Dispersion — wave splitting up by frequency
  • Rectilinear propagation — the movement of light waves in a straight line also helpful for seismographs


Examples of waves include:

Standing wave

Standing wave in stationary medium. The red dots represent the wave nodes

A standing wave, also known as a stationary wave, is a wave that remains in a constant position. This phenomenon can occur because the medium is moving in the opposite direction to the wave, or it can arise in a stationary medium as a result of interference between two waves traveling in opposite directions.

The sum of two counter-propagating waves (of equal amplitude and frequency) creates a standing wave. Standing waves commonly arise when a boundary blocks further propagation of the wave, thus causing wave reflection, and therefore introducing a counter-propagating wave. For example when a violin string is displaced, longitudinal waves propagate out to where the string is held in place at the bridge and the "nut", whereupon the waves are reflected back. At the bridge and nut, the two opposed waves are in antiphase and cancel each other, producing a node. Halfway between two nodes there is an antinode, where the two counter-propagating waves enhance each other maximally. There is on average no net propagation of energy.

Source: wikipedia