Physics 101 Blog #1
Japan Air Lines Flight 123
Everybody knows of the tragic accident of Japan Air Lines Flight 123 in August 12, 1985 near Mt. Fuji, killing more than 500 passengers and making it the deadliest aviation disaster involving a single aircraft in history. After official investigation, there are many physics-involved elements that took place before and during the event.
A few years before the accident, the same aircraft was involved in a minor tail-strike accident, in which the rear of the aircraft came into contact with the runway tarmac upon landing. The resulting friction damaged the rear pressure bulkhead, which is a dome-shaped cover located right under the tail that keeps the cabin and fuselage pressurized at a near sea-level temperature.
A repair was carried out by patching up the scratched bulkhead with a strip of rivets, but this procedure was improper as two rolls of rivets were required to complete the repair. The faulty bulkhead would continue to sustain pushing and pulling forces of air pressure changes after each take off and landing, gradually weakening the area of the faulty repair until on August 12, 1985, reached its breaking point known as metal fatigue, and causing an explosive decompression as the bulkhead finally burst. Below is a force diagram of the pressurized air acting against the bulkhead of a typical Boeing 747, while it's on the ground and 35,000 ft in the cruising altitude:
When the catastrophic decompression occurred, the sudden explosion of air rushing out of the cracked bulkhead sheared off the tail section and destroyed the hydraulic lines, which is a critical system for maintaining flight controls of the elevators, ailerons and rudder. The aircraft entered into an uncoordinated cycle of up and down movement, known as the phugoid cycle. An example diagram is provided:
Since the movement controls were nearly all uncoordinated, the plane literally acquired a mind of its own. It began to fly up at a steep angle, where it reaches a point called "angle of attack", which is the minimum angle in which the plane's nose is lined up with the horizon before a stall takes places. With a steep angle, massive amount of friction is produced in the undercarriage as huge amount of air resistance slows the plane into a stall. The plane stalled, and the nose immediately falls downward, and the aircraft goes into a steep dive until it regained air speed and lift force and went back up again. JAL flight 123 had to endure this cycle several times within a 30 minute interval until it went into an unrecoverable nosedive and crashed straight into a mountain range, killing more than 500 passengers and crews and sparing only 4 survivors.
One last interesting thing to note was that the four survivors of JAL flight 123 were all seated in the very rear of the plane. When the plane struck ground, it went in as a nosedive at a very fast speed. Massive amount of momentum was exerted on to the aircraft, leaving the majority of plane parts and passengers alike mashed into compressed pieces of unrecognizable chunks. However, the majority of the rear tail section was still intact, due to the fact that all momentums required for the moving object to stop had been used and sparing the lives of some passengers at that location.
Physics Blog #2
Voyager 1 Space Probe
Voyager 1 is a man-made satellite, and the first artificial object to be able to travel into interstellar space. Launched in 1977, Voyager 1 is currently traveling at 17 km per second, also making it the fastest man-made object, and at a distance of 19 billion km from Earth also makes it manmade's most distance object. But, how is the Voyager capable of traveling such distances, and at such speed?
Space is a vacuum and a frictionless environment. Without the influence of gravity or other intercepting objects, an object can travel on an on at the same speed and direction forever and ever. This is known as the constant velocity, in which an object's speed stays the same, without being influenced by acceleration.
The constant velocity of Voyager 1 is at 17 km/sec, which means that it would be the speed it will remain, possibly forever, if left undisturbed or not influenced by other gravitational forces.
Physics Blog #3
Jet Engine Reverse Thrust
When a plane lands on an airport, it cannot depend on wheel brakes to slow down like cars and trains. Instead, it relies on an engine mechanism called reverse thrust (a.k.a. speed brakes). Just as thrust is required for a plane to speed up to obtain lift and to keep it airborne, reverse thrust is deployed to reverse the air flow of the engine. What happens during normal flight is that air is sucked in through the front, where the fan blades are located, compressed in a compressor, mixed and combusted along with jet fuel, and released through the rear nozzle in a very pressurized and rapid fashion, just like nitrous oxide on race cars. This flush of high pressurized air propels the plane forward, but when the opposite happens, the air is being diverted to other than the rear end, usually forced out from the side (as seen in the pictures and diagram above). The following aircraft force diagram is provided to give a better reference to the common forces affecting an airplane.
Blog #4:
The San Andreas Fault:
Everybody knows the infamous San Andreas fault, a transform fault line located along the West coast of California that makes up the Eastern-most region of the Pacific's Ring of Fire. The San Andreas Fault is made up of two major tectonic plates, the Pacific Plate and the North American Plate, sliding against each other. The resulting friction of those two massive plates produced some of the most well known earthquakes such as the 1906 San Francisco quake and the 1989 Loma Prieta quake.
Why is the San Andreas fault transform the western landscape so much and at the same time, produced and will continue to produce destructive earthquakes? Well the crevices in between the two massive plates are even, but rather jagged, and for the sliding to occur won't be smooth, especially if the two plates got tangled up. When it happens, both plates would try to shove across each other, but only get more interlocked. The resulting forces may result in the landscape near the fault line to look wrinkled. Eventually if the area gets completely tangled, potential energy began to build up on the part where pressure is exerted the most, until one day the end snaps, releasing massive amount of energy when the plate suddenly shoved pass it in an instant, and the resulting shockwave is what produces the destructive force of earthquake.
Blog #5
Terminal Velocity vs Precipitation
Nearly all precipitation, rain, snow, sleet, or hail originated from clouds that are high up in the sky. But since they fall from such an extreme altitude, why don't they hit the earth in a rapid speed that would have probably left a crater on the ground after impact? When water vapor in clouds condenses, it forms into bigger droplets which eventually gets overtaken by the force of gravity and falls. For a while its falling speed increases. However, air resistance soon began to take over and pushed the precipitation from below. Eventually, the air resistance force would equal up with the gravitational force, in a situation called terminal velocity, and the precipitation fall rate stabilizes. The precipitation would maintain this fall rate until it makes contact with the ground or comes in contact with wind shears or other moving air along the way.
Blog #6
Air Hockey Table
Air hockey is not only a type of fun game, but it also serve as a great representation of how objects can behave when forces of physics are being applied in an environment with no friction (and decreased air resistance). The lack of friction was emulated by the table vent fans blowing from the surface up, which allowed the puck to "float" with the air pushing its bottom. A puck was to remain stationary until initial force was applied, and it would move at a constant velocity, which means that it would not be accelerating, until an additional contact force was to be applied.
