RTB24's Blog

I'm sitting in the commons. Enjoying my Friday morning, of course. But suddenly, I am awakened to the thought of physics. Not actual physics, but a deadline! I needed to finish my blog posts! And now I sit, with two other helpless Physics C students, as we plow through some blogs.

As I sit, inactive, I burn about 100 calories per hour. Which, suprisingly, is not too bad. So I'm actually excercising.

If you just sit, however, you burn a suprising 65 calories per hour - the energy it takes to simply stay alive and maintatin bodily functions.

So, while writing this blog post, I've used about 52.3 joules of energy. Workout complete.

Sure, jogging for an hour will burn upwards of 500 calories, but I'm not training for the olympics.

Considering this is a physics website, everyone that reads this post will have probably already known what "g-force" is.

But I'm going to talk about it anyway.

Whether you're sitting, standing, or walking while reading this - you're experiencing about +1g. All that means is that you weigh exactly what you weigh. So, if you weigh 150 pounds and you're experiencing +1g, that means you weigh 150 pounds. Simple.

But what if you stood upside down? Are you still under +1g? It sure doesn't feel like it, especially with all the blood in your body rushing to your head.

All in all, you're under 1g. The act of flipping yourself over doesn't change any centripetal force...just your human perception.

However, there are various ways to change your "g" level.

Try a centrifuge, for example.

Used to train pilots and astronauts, centrifuges spin around a fixed radius, creating values of up to 9 or 10g - which can get pretty funny.

A pilot undergoing 9g doesn't look very attractive. Their eyes attempt to disembark from their heads; everything is pulled down at nine times its original weight.

An average 170 pound man, under 9g, weighs a whopping 1530 pounds. The centripetal force results in a pulling action on the subject; blood rushes to the lower extremities, leaving the brain in a severe lack of blood. Which is hilarious to watch, but can be extremely dangerous.

G-force has the ability to kill pilots in the blink of an eye. Called G-LOC (G-force induced loss of consciousness), this event is pretty much a killer. Pilots, either cocky or untrained, sometimes pass out when they're under high G-force. The lack of blood in the brain makes the pilot slowly and steadily black out.

Personally, I've only felt 4g, and even that's uncomfortable.

So how did the aviation community overcome G-LOC?

The answer was in the form of an inflatable suit...commonly known as a "G-Suit". Attached to a pilot's flight suit, the apparatus will inflate around the legs and lower abdomen when high G-force is detected. The compression pushes blood back up to the head, so the pilot retains consciousness.

On July 6th, 2013, an incident occurred that could have been avoided.

A massive (up to

Asiana Flight 214 was no exception.

So, how did the 777 fail to make it to the runway? The answer is annoyingly simple. The pilots (one of whom performing his first landing in a 777 at San Fran) forgot to monitor the most important gauge in their aircraft: the airspeed indicator.

The NTSB reported that the standard approach speed for a 777 is about 137 knots (160 mph, for comparison). Flight 214 came in at a VERY slow 112 knots.

In this case, the pilots were literally on autopilot. They were using "autothrottle", a device that allows pilots to pre-set an airspeed. But using autothrottle doesn't give the pilots an excuse not to monitor their airspeed.

As they flew their approach, they were indicated below their proper glidepath. In other words, they were too low. Their natural reaction was to "pull-up", or pull on the stick, thus raising the nose of the aircraft.

Normally, pitching the nose up will simply make the aircraft gain altitude. But not when you're flying at a dangerously slow 112 knots.

Here's where the physics comes in.

Raising the nose increase Angle of Attack. This angle is defined as the angle between relative wind and the wing itself.

If this angle becomes too large, the aircraft will enter what's called a "stall". No, that doesn't mean the engines quit. It means that the wing no longer produces enough lift to overcome the downward force due to gravity, mg.

The end result is obvious. The aircraft stalled. The pilots failed to recover from the stall. In fact, they FURTHER increased the angle of attack, dooming the aircraft.

This is why the safest pilots are the ones who don't rely upon autopilot.

We've all heard of the famous "sonic boom" when a jet or rocket passes overhead at a speed greater than the speed of sound. Sound waves are fundamentally compressed tightly behind the object, creating the "bang". But if that is possible with sound, could it be possible with light?

Yup.

"Photonic Booms", as they're called, are created in situations where light waves aren't given enough time to radiate out into their own paths; they're constricted and are densely packed into each other. This creates constructive interference, creating massive amplitudes of the waves. A "photonic" boom.

Astronauts have historically complained of bright flashes in their eyes in space. The answer could very well be high speed particles that move faster than the speed of light (in air), but not faster than "c". The particles then create a photonic boom, right inside the astronaut's body.

So, even if those particles are moving slower than c, is it possible to break the universal speed limit? A common misconception is this scenario:

You want to push a button that is exactly one light year away. So, the fastest possible object, light, would take a year to get there, correct? But maybe there's an alternative. What if you had a board of something (wood, for example), and the board was one light year long? And if you placed the board in between you and the button, and then pushed the board (therefore pushing the button), did you just break the speed of light? As optimistic as it sounds, no. When you "push" something, you're moving it with small compression waves that move at the speed of sound in that material. So, sadly, if you were to push the board, it would take a VERY long time for the board to even collectively move in the direction of the button.

The universal speed limit, in this instance, is maintained.

We've all heard the rumor that a penny (dropped from the top of the Empire State Building, or any skyscraper) could kill you if you were an unlucky soul at the bottom. Unfortunately, that doesn't exactly work out. The solution is easy: get rid of air. But that's not practical.

So how fast would a penny actually fall? The answer is found when we consider the idea of terminal velocity; the point at which drag force equals the force of gravity. Although asymptotically approached, acceleration, at a point becomes negligible; the object will refuse to fall any faster. "Air friction" simply won't allow it.

As it turns out, the terminal velocity of a copper penny is under 100mph. You might get a nasty bruise, but you won't be dying anytime soon.

Another ill-informed myth is that Isaac Newton discovered gravity because an apple fell on his head. Sadly, that never occurred. He did, in fact, watch apples fall to the ground at his mother's farm, and was inspired by the downward motion of the apples. This simple observation led Newton to eventually "create" calculus, understand orbital motion of planets, among other fantastic discoveries.

Additionally, there's a misconception that Albert Einstein failed mathematics as a child! Einstein ended up doing very well in school. But what IS true is that Einstein started to talk very late in his "toddler-hood" at about four years old. Einstein, in general, was a very good student and briefly considered becoming a mathematician, until he realized he could study physics to a better degree.

Imagine living life as a frictionless surface. Imagine getting out of bed, letting your feet hit the ground, and eternally slipping...until you can grab something to stop you, correct? Chances are, your hand would slip as well. Friction is extremely important...and it makes our lives livable. The coefficient of friction of rubber shoe tread (on dry asphalt) is an astonishing .9! We don't notice it, but our shoes are very frictional. The MythBusters did a segment on friction when they busted of the myth of the "banana peel" slip commonly seen in cartoons. Although the myth wasn't exactly true, banana peels DO in fact decrease friction by a considerable amount...or at least enough to make Adam Savage look like an idiot in this clip:

Rubber is one of the most commonly available materials with a very high coefficient of friction, making it feasible for civilian clothing use. Its coefficient is maximized when contacted with asphalt, or any concrete surface (making rubber a great choice). However, metal-on-metal coefficients of friction are sometimes higher. When one examines the lattice structure of metallic atoms, small pieces of the other metal will be lodged into the other metal. No matter how smooth you make something (realistically), there'll always be tiny "welds" and "tears" on both surfaces.

Thank friction. Don't slip.

The average aircraft will usually suck up a couple thousand feet in order to stop. The average single piston engine aircraft will take less, and a 747 will take much more (>5000ft).

This creates a problem. Aircraft have insane amounts of momentum upon touchdown, and pavement isn't cheap. In addition, we can't have "mobile" airports for military use - so how are we able to deploy combat ready aircraft to anywhere in the world within a matter of hours?

Well, we made mobile airports. And, they float!

The aircraft carrier was first used in 1920. Essentially, it was a floating street where some aircraft landed, and others careened into the ocean, killing their pilots. There was no effective and safe way to stop aircraft on such a small distance.

As of 2013, things have changed. The modern aircraft carrier is a small metropolis, with crews of more than 2,000 sailors. The technology has improved to a point where we're able to launch and recover 90 aircraft on the same ship.

But how do we do it? Simple - Hydraulics!

Laid across the aircraft carrier's deck are four wires. When an aircraft, like the F/A-18 in the video below, hits the deck, the aircraft "catches" one of those wires on a hook attached to the fuselage of the plane. The wire then rapidly sends kinetic energy of the aircraft to "hydraulic dumping systems" that, in simple terms, tug on the aircraft until it's stopped.

It's like a ship with massive, hydraulically-backed rubber bands.

But landing is only half of the story.

How does the F/A-18 launch from the carrier? Sure, it could take off like a conventional airplane, but the runway is far too short! The aircraft would simply fall off the deck. *insert splashing noise here*

We needed some sort of "catapult" to get the aircraft moving fast enough so that the wings could produce more lift than the aircraft's weight.

So, we used what we were experts in - Steam! By pressurizing a tank to very high PSIs, that potential energy is released, dragging the aircraft by yet another hook across the deck with a final velocity of anywhere between 120-150 Knots. These catapults will soon be replaced by electromagnets, that use electric currents to create strong magnetic fields to propel the aircraft into the air. These systems are far less expensive than conventional steam catapults.

To be honest, I was hesitant when I was asked to take AP Physics B two years ago. I certainly had no idea what to expect. As it turns out, I wasn't disappointed. The class itself was intriguing and it motivated me to continue my education in Physics.

As a student pilot, I became interested in how the fluid dynamics actually played out in the air. Last year gave me some important insight on that topic. I became interested in physics beyond the areas of last year, leading me to enroll in this class.

I suppose I'm taking AP-C for the experience; that's what I want out of this class. I aspire to be a full time pilot (with a mechanical engineering major), and the knowledge (and maybe the college credits) will certainly come in handy.

This year, I hope to expand my interest and skill in the physical setting. I have big expectations for myself in this class, and I'm interested to see how well I can do.

I'm very excited about going further into E & M, because I feel like I never actually grasped the concepts last year. However, the math itself will be challenging, and that's what I'm mainly anxious about as I go through these first few weeks of senior year.

Since flying is easily my favorite thing to do, I couldn't think of a class that applied any better to flight than physics.

So, Physics C, bring it on.