Magnificent sand magnified 300 times, 99% is biological remains... Korean sand is mainly minerals

What does beach sand look like when magnified 300 times? In EP.219 of the 'Looking at Science' channel on 'BODA', MC Jung Young-jin, astronomer Professor Ji Woong-bae, physicist Professor Kim Beom-jun, and geologist Professor Kim Gi-beom appeared to answer viewers' curiosities. The first question was that when sand was magnified, it looked very different from the expected appearance of sand.

Magnificent sand photos, almost 99% are biological remains

The screen showed repeating honeycomb patterns, snail or shell shapes, sharp tripod-like shapes, and long green grains like plant stems. To jump to the conclusion, the cast explained that almost 99% of what is here are biological remains. Some are parts of broken shells, and even marine plankton are not entirely jelly-like but all possess skeletons. These skeletons are largely divided into two types, one of which is a silicate (SiO4), namely a silica skeleton, which can become an exoskeleton or an endoskeleton.

When plankton flourish and then die all at once, the soft parts decompose and only the skeletons remain. When plankton with silicate skeletons flourish in large quantities like a red tide and then die and accumulate, they become diatomaceous earth, a rock made of those skeletons. However, the cast pointed out that the grains in the photos do not appear to be the result of a specific species flourishing in large quantities, but are traces of very diverse marine planktonic and benthic organisms. They explained that if you just scoop up sand, it doesn't look like this, and that these are photos with a bit of staging, where different-looking things were picked out one by one and placed under a microscope for a long time. They added that skeletons of living organisms might be mixed in between beach or riverside sand, and such organisms mainly live in abundance in subtropical seas.

Haeundae is quartz, Caribbean is coral... the reason why sand colors differ

What would happen if you scooped up Korean sand and looked at it through a microscope? The cast replied that Korea's sand is mainly minerals. Broadly speaking, rocks that were on land undergo weathering and erosion to gradually become the size of sand grains. Sand does not have a specific definition but is a concept of size, where substances between 64 micrometers and 2 millimeters in diameter are called sand. There is also biogenic sand, and if volcanic ash from a volcano is the size of sand, it can be called volcaniclastic sand. An explanation was also given that the black sand in Iceland is volcanic ash composed of basalt.

The reason why the Haeundae seaside, commonly called a white sand beach, is relatively white was also introduced. The rocks on land are mainly granite, and the minerals that make up granite are quartz, feldspar, and mica. Biotite is black, feldspar is opaque and yellowish, and quartz is transparent, white, and bright. Since mica and feldspar are extremely vulnerable to weathering, breaking easily mechanically and decomposing easily chemically, quartz is what survives at the end as it flows along river water. When this quartz is gathered, it becomes a white and sparkling white sand beach.

The reason why Caribbean beaches are exceptionally white is that they are very warm seas near the equator, so biological productivity is extremely high. Many plankton and corals with calcareous skeletons are produced, and as the corals die and their remains are broken by waves to become sand, they become even whiter beaches than the quartz-made Haeundae beach. An extreme contrast can be seen at Udo Island in Jeju Island. On Udo Island, within one island, there is Geommeolle Beach, where black basaltic volcanic ash created by volcanic eruptions is eroded by waves and accumulated, and Rhodolith Beach, which is the whitest sea seen in Korea. Red algae absorb calcium carbonate in the sea to create structures and live attached to them, creating pea-sized pebbles or small sand-like grains, and these grains are white because they consist of calcium carbonate, namely lime.

Swinging your arms when falling makes your body lean forward

The second question came from a summer MT video. Physicist Professor Kim Beom-jun, who was considered the weakest, came in first in a pushing contest with his arms, because at the moment he was about to fall, he swung his arms frantically, which delayed the time of falling quite a bit. To the question of whether swinging arms is physically effective, the cast explained it with what is called the conservation of angular momentum in physics.

Examples given were drones and swivel chairs. In a drone with four propellers, they spin in opposite directions in pairs. This is because if they all spin in the same direction, the drone body itself would spin in the opposite direction. For a helicopter with one propeller on top, it uses an auxiliary propeller to prevent the direction from turning sideways. It is the same principle that when you sit on a swivel chair, lift your feet off the floor, and spin your body quickly, the chair spins in the opposite direction. The explanation was that when falling backward, if you swing your arms, your body must rotate in the opposite direction of the arm swing, and as a result, your body leans forward. The cast said it was fascinating that the body instinctively knows to do this at that moment.

At this time, the arms must be swung while gradually increasing speed, and acceleration is important. To prevent falling, people with long arms and heavy fists have an advantage. This is because angular momentum increases the further the distance from the center of rotation to the rotating object and the faster it rotates. To the question of whether one could maintain a tilted state without falling if they spin very fast, the answer was that it would actually not be easy because one must overcome the torque of falling caused by gravity.

The principle also seen in humanoid robots and long jumping

People researching this principle made small robots and had them rotate their arms with motors when they were about to fall, and then the robots stood up again. It was mentioned that when making humanoid robots these days, whereas previously they tried to make them as stable as possible, they now teach them to move in the direction of the movements humans make when losing balance. There was an experiment where a robot that could not move its arms fell well, and it is said that if a person's arms are tied, the possibility of falling increases even if the center of gravity shakes only slightly. The explanation is that tightrope walkers who stretch a rope between buildings always hold a long pole because it is advantageous the longer the pole is.

The movement of arms is also revealed in long jumping. When athletes jump at first, they put their hands forward, and when landing, they put their hands backward. Even if heavy fists are sent backward, the center of gravity of the body remains the same, but since the feet can go forward, it is said that landing athletes should put their arms backward as much as possible so that their feet can move forward. The cast said that for athletes competing by fractions of a second, each of these postures could have quite an influence.