Explanation of words in "The Special Theory of Relativity"

Special: The word "Special" in name arises because we employ only unaccelerated reference frames, not all reference frames  that one can think of. In other words, we "specialize" to the way things appear when observed from uniformly moving reference frames.

Relativity: The word "Relativity"  comes from a phrase coined by Henry Poincare, an eminent French Physicist and Mathematician.

In 1904, Poincare was invited to address the international congress of Arts and Science, held in St. Louis to commemorate the 100th Anniversary of Losiana purchase. "Poincare" spoke of "Principle of Relativity".

In his words.....

Assume that you are in plane on its way from Chicago to Pheonix, another plane making the return flight, over wheat fields of Kansas. A farmer, looking up, notes that you are flying south-west at 500 miles/hr relative to his wheat fields. The pilot of return flight notes that the distance between the two planes is decreasing at about 1000 miles/hr. So far as the pilot is concerned, you are travelling at about 1000 miles/hr relative to his plane.

The essence is this:

Statements about uniform motion relative to a specified reference frame-wheat fields or another air plane are meaningful.

       A quantitative statement about uniform motion with out specification of a reference frame is not meaningful. Why? because our principle 1 says we cannot discern uniform motion with out recourse to some reference frame.

Take first the colloquial form of that principle: If we are in unaccelerated vehicle, its motion has no effect on the way things happen inside it. So by just doing experiments inside the vehicle, we have no way to assign a velocity to the vehicle. Only if we look out of window and there by use wheat fields of Kansas as an outside reference frame- we can decide on velocity (relative to that outside reference frame).    

Theory: It appears because principle 1 &2 are generalizations from observation and experiment.

 

Principles of Special Theory of Light

PRINCIPLE-1

Colloquial Statement: if we are in unaccelerated vehicle, its motion has no effect on the way things happen inside it.

Formal Statement: The laws of physics are same in all unaccelerated reference frames.

PRINCIPLE-2

The motion of light is not affected by motion of source of light.

what does MWe mean? what does the 'e' stand for?

M- Mega ; W-Watt; e-Electrical

Unit used to denote power level in Power Plants.

It is used to denote Electrical Power Generation by Power. It is denoted so as to differentiate it from thermal power generated. Not all thermal power can be converted into electrical but it depends on efficiency of plant. 

What causes the "white smoke" trailing high flying jet planes ?

Modern turbofan (jet) engines actually mix with fuel only a small portion of the air they suck in. The vast majority (90% or so) of air is "bypass air" that is compressed and then used for additional thrust. This air expands as it leaves the engine.


All engines that burn petroleum-based fuels (jets, piston engines, etc.) produce steam and CO2 as their exhaust. The CO2 is invisible on exiting the engine and stays that way, but in cold air, the steam condenses into liquid water or ice, forming a white mist that leaves a trail behind the aircraft. This trail is called a condensation trail, or contrail.


Contrails may or may not be visible, depending on atmospheric conditions. They are common above 26,000 feet, but uncommon below. Again, depending on atmospheric conditions, they may be completely absent, or they may disappear after a few minutes, or they may grow into ordinary cirrus clouds.

How does an atomic clock work?

The term atomic clock is the general name used to describe any variety of time keeping devices based on the regular vibrations associated with atoms.

One of the first atomic clocks or as it is also known the ammonia clock. Was developed by the National Bureau of Standards, and was based on the measurements of the vibrations of atoms of nitrogen, oscillating back and fourth in ammonia molecules at a rate of 23,870 vibrations per second.

The modern day atomic clocks are based on caesium atoms. The spectrum of caesium includes a feature corresponding to radiation with a very precise frequency of 9,192,631,770 cycles per second. One second is now defined as the time it takes for that many oscillations of the radiation associated with this feature in the spectrum of caesium. This type of clock is known as a Caesium clock and it is accurate to one part in 10,000 billion, or one second in 316,000 years.

Even more accurate clocks have been developed using radiation from hydrogen atoms. They are known as Hydrogen Maser Clocks, and one of these clocks, at the US Naval Research Laboratory in Washington, DC, is estimated to be accurate to within one second in 1.7 million years. In principle, clocks of this kind could be accurate to one second in 300 million years!