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Relativistic travel and ageing

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Today’s doubt- If i am moving at constant speed of 0.5 times speed of light away from another person, it means both mine and his frame of reference are inertial (since both are not accelerated), then in my frame that person is moving away from me at 0.5 times speed of light and by special theory of relativity, he would be younger than me. But in his frame of reference I am going away and I should be younger. Actually who is getting younger and why?

Akshay Ramachandran asks

Rotation of a ball in mid air

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Hi, i’m working for a company where we use gyroscopes to measure the rotation of a ball in 3 dimensions. The output from the sensor is sent 25 times a second and is then converted to deg/s in each of the three axis’s. My task is to analyze the data and then create a program using it. I have some questions regarding this.

1. How do i find a good approximate of the total rotation of the ball in one number. The rotation change (not a lot but it makes things hard) in each of the axis’s while it’s airbourne, but when i use the following formula: sqrt((rotationX)^2 + (rotationY)^2 + (rotationZ)^2) i get almost zero total change of rotation. Is it correct, and why?

2. If i want to measure the total change of rotation between two consecutive samples, is it then correct to use this formula:
sqrt((^2 + (^2 + ( – rotationZ.last)^2). Why or why not?

Bonus: Does anyone know what or how the gyroscope measures?
Is it torque, just rotation in general or something else?

Heat & Cold

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My brother was arguing that heat & cold could be separate entities and I’ve told him what is known is that cold is the absence of heat and they are just a representation of one thing similarly to how darkness is an absence of light. Having told him that, he asks why are they not considered similar to salt & water? This lead to an interesting thought experiment. At 1st I highlighted the obvious to him of the tangible chemical formation of salt & water making them separate and detectable so, whereas you can’t do the same with heat and cold they aren’t detectable both there. This is when he says that maybe they are. And having recently read about the lucid fallacy, I decide to hear him out, casting aside common examples that show they are a mere representation of low and high temperature.  He basically said if they aren’t separate entities wouldn’t a vacuum have no temperature rather than be cold?


Travelling back in time by increasing speed?

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Is it true statement that travelling faster than speed of light and travelling back in time both are same ?

Asked  Chandan Kumar




Though travelling back in time is implied based on the formulas of theory of relativity, physically going back to past is not yet achieved.

The following posts may enthuse you.

However, as famous Theoretical physicist and string theorist Brian Greene, of Columbia University, said: “You can build a spaceship, go out into space [and travel] near the speed of light, turn around and come back. 

“Imagine you go out for six months and you turn around and you come back for six months.”

While you are travelling at the speed of light, time stays slow relative to the people who are standing still back on Earth.

As a result, you would be going fast while your clock would still be going slow.

Prof Greene: “When you step out of your ship, you’re one year older but Earth has gone through many, many years. 

“It can have gone through 10,000, 100,000 or a million years depending on how close to the speed of light you traveled.”

However, the only problem is that a machine travelling at such speed would require an “unimaginable” amount of energy, while the stress from the centrifugal force on the body would likely prove fatal

Greene says: “No one has given a definitive proof that you can’t travel to the past.

“But every time we look at the proposals and detail it seems kind of clear that they’re right at the edge of the known laws of physics. 

“And most of us feel that when physics progresses to a point that we understand things even better, these proposals just will be ruled out, they won’t work.”

Time Period of a Simple Pendulum

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The time period of a simple pendulum of length L fixed on the top of a rocket moving upwards with a constant acceleration g is .. ?

Asked Amandeep

Projectile Motion

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A projectile is projected at an angle theta with horizontal with speed u . If air resistance is taken in account , the angle with vertical at the time of hitting the ground will be a)more than (90 + theta) b)less than (90 – theta) c)(90 + theta..

 Iman Bint e Abbasi

moving through parallel universes

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could it be theoretically possible for a person to die in a certain universe and wake up in a similar universe like a shift leaving that person being the only person aware of this change, also could everyone be one and the same person like one consciousness experiencing itself in many different ways at the same time

Asked Paul Appleby

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Half Yearly Exam Count Down

Half Yearly Exam Count Down KVS Ernakulam RegionOctober 17th, 2017
The Half Yearly Examination for Kendriya Vidyalayas of Kerala starts from 17 October 2017
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