Director Kevin Insik Hahn of CENS used to ride his bicycle to school in Seoul during his teenage years, despite dangers associated with road traffic conditions and general disregard for cyclists’ safety then. He was one of the few who commuted to and from school by bike, but had to promise his mother only to use roads for pedestrians and cyclists.
Several decades later, Kevin resumed biking after moving to the Institute for Basic Science in Daejeon. Compared to the past, the road infrastructure for cycling has now evolved to be much more safe and enjoyable. Riding along the fields ripe with cosmos flowers and feeling the air resistance in autumn provide a relief from everyday stress in life, as well as hope for restoring leg muscles.
What is the reason that travelling by bike is faster than by foot, while using less energy? The difference lies in friction. One cannot propel oneself in the absence of friction, but too much of it will soon halt any momentum. Every footstep requires energy to overcome the friction between the shoe and the ground, and the gravitational pull of the body during the rising motion. In contrast, the tires on a bike meet only small areas of the surface and a much lower friction is induced.
Another important physical aspect for methods of transportation is air resistance. An ordinary object experiences air resistance which is proportional to the square of the speed of the object relative to air. By the same principle, a falling object like a raindrop reaches an innocuous terminal velocity even when it is released from a cloud several kilometers above ground.
A bicycle is one of the most efficient and environmentally friendly transportation devices for mankind. A car is much more massive than a bike, and the energy needed to travel the same distance is at least 50 times greater. A projectile into space is arguably the most sophisticated transportation device, as it needs to overcome the Earth’s gravity and substantial air resistance while carrying heavy objects such as a satellite.
Last Thursday, a domestically developed space rocket called Nuri was launched from Korea with public enthusiasm. The event was a testament of the nation’s technological advancement, and also a source of strength during these trying times. Hahn would like to celebrate and honor the development of Korea’s space program towards a grand milestone.
Link to the original column (in Korean): https://www.seoul.co.kr/news/newsView.php?id=20211026029012
Center for Exotic Nuclear Studies