GIANT SPRING

You can observe two kinds of waves.

Making the spring oscillate left and right in a perpendicular direction compared to its length, you will produce transverse waves, such as sea waves or light waves (which are electromagnetic waves).

Pressing or stretching the spring lengthways, you will produce longitudinal waves such as sound waves.

DANCE OF THE PENDULUMS

The period of oscillation of a pendulum only depends on the length of its string. All the pendulums have a different length, so they will not stay synchronized. They will create various patterns of oscillation from order to chaos, then back to order, with moments of  singular beauty and symmetry.

A pendulum with a long string will swing slower than a pendulum with a short string; so after a certain number of oscillations equal to the least common multiple of all the pendulums' periods of oscillation, they will come to the initial configuration again.

PASS OR NOT PASS

The experience you’ve just made is called polarization.
Light is a transverse wave that oscillates on a plane perpendicular to its direction of travel.
Usually light waves are free to vibrate in every direction, but Polaroid plates, the material which the lenses and the panel are made of, only select oscillations that take place on a certain plane.
If the plane of polarization in the glasses is oriented in the same direction as that of the quadrant, then the light passes through and you’ll see that part enlightened; if it’s perpendicular, then the light doesn’t pass and you will see that part dark.

RESONANT PENDULUMS

Two pendulums with same lenght suspended from a common support will swing back and forth if the support allows the motion of one pendulum to influence the motion of the other. Every pendulum has a natural or resonant frequency, which is the number of times it swings back and forth per second. The resonant frequency depends on the pendulum’s length. Longer pendulums have lower frequencies. Every time the first pendulum swings, it pulls on the connecting string and gives the second pendulum a small tug.

Since the two pendulums have the same length, the pulls of the first pendulum on the second occur exactly at the natural frequency of the second pendulum, so it (the second pendulum) begins to swing too. However, the second pendulum will swing slightly out of phase with the first one. When the first pendulum is at the height of its swing, the second pendulum is still somewhere in the middle of its swing.

As soon as the second pendulum starts to swing, it starts pulling back on the first pendulum. These pulls are timed so that the first pendulum slows down.

The pendulums repeatedly transfer the motion back and forth between them this way due to resonance.

In physics, resonance describes when a vibrating system or external force drives another system to oscillate with greater amplitude at a specific preferential frequency.

A familiar example is a playground swing, which acts as a pendulum. Pushing a person in a swing in time with the natural interval of the swing (its resonant frequency) makes the swing go higher and higher (maximum amplitude), while attempts to push the swing at a faster or slower tempo produce smaller arcs. This is because the energy the swing absorbs is maximized when the pushes are "in phase" with the swing's natural oscillations, while some of the swing's energy is actually extracted by the opposing force of the pushes when they are not.

SAND DRAWINGS

When resonating at a specific frequency, a metal plate is divided into regions that vibrate in opposite directions (antinodal lines), bounded by lines where no vibration occurs (nodal lines). In physics we call them standing waves. In one dimension, One easy example to understand standing waves is two people shaking either end of a jump rope. If they shake in sync the rope can form a regular pattern of waves oscillating up and down, with stationary points along the rope where the rope is almost still (nodes) and points where the arc of the rope is maximum (antinodes).

With Chladni plates we could see 2D standing waves, where nodes and antinodes are lines instead of points. By convering the plate with sand, the vibration causes the sand to move and concentrate along the nodal lines where the surface is still, outlining the nodal lines. The geometric patterns formed by these lines are what are now called Chladni figures.

Changes in the Chladni figures occur when frequency changes, since metal plates have more than one frequency of resonance.

THE SHAPE OF A WAVE

Normally, strings vibrate so rapidly that your eyes can’t see them. But when the cylinder spins the white stripes pass behind each string from top to bottom, completing many, individual, top to bottom scans of each string.

The phenomenon of persistence of vision blends the multitude of top to bottom scans into a single image, the wavy line.

When you look at the strings, the wavy lines that you see show you how the strings behave when they vibrate to produce sound. Both the tension and the length of a string effect the frequency of vibration (pitch of the sound). Shorter or tighter strings vibrate faster to make higher tones. Longer or looser strings vibrate slower to make lower tones.

Compare the number of waves that you see on a short or tight string to the number of waves on a longer or looser string.
The number of waves that you can count on each string relates to the frequency of vibration.