Strange sum (riddle tread)
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08-09-2011, 01:26 PM
 
RE: Strange sum
(08-09-2011 01:13 PM)The_observer Wrote:  The train also has a lot more mass Smile

You still have not explained the basic mystery:

Fact#1: The speed of the fly MUST be zero for a billionth of a second before it starts accelerating backwards.

Fact#2: The fly is pasted on the train, in direct contact with it

Conundrum: If we accept Fact#1 and Fact #2, how is it possible for the train not to have a speed of zero for the same billionth of a second?

Big Grin
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08-09-2011, 01:39 PM
RE: Strange sum
(08-09-2011 01:26 PM)Zatamon Wrote:  
(08-09-2011 01:13 PM)The_observer Wrote:  The train also has a lot more mass Smile

You still have not explained the basic mystery:

Fact#1: The speed of the fly MUST be zero for a billionth of a second before it starts accelerating backwards.

Fact#2: The fly is pasted on the train, in direct contact with it

Conundrum: If we accept Fact#1 and Fact #2, how is it possible for the train not to have a speed of zero for the same billionth of a second?

Big Grin

Because speed is relative to other objects...
The zero speed you imply is zero speed difference between the fly and the train. There is however a very brief moment where the fly also has zero speed between her and the earth, the exact same moment her ass goes trough her brains.

Observer

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08-09-2011, 02:14 PM
 
RE: Strange sum
I guess I have tortured you enough. Sad

The precise answer, given by physics, is the rejection of the unstated (and maliciously smuggled in) assumption that both the fly and the train are rigid bodies. They are both composed of billions of molecules (guess which of them has more?) and, while individual train- and fly- molecules collide as quasi-rigid bodies and both bounce back, the rest of the train molecules keep moving forward, easily shrugging off the slight elastic tug exerted on them via the lattice-like molecular structure of the metal. But, because of the law of ‘conservation of energy’ in physics, the train’s speed will also drop an infinitesimal amount to account for the change in the kinetic energy of the fly-molecules.
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08-09-2011, 02:21 PM
RE: Strange sum
The fly isn't realy a fly anymore after the encounter...
So you can even argue that the fly never goes to 0 km/h since at that moment she isn't a fly anymore.

Observer

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Disclaimer: Don’t mix the personal opinion above with the absolute and objective truth. Remember to think for yourself. Thank you.
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08-09-2011, 02:23 PM
 
RE: Strange sum
(08-09-2011 02:21 PM)The_observer Wrote:  The fly isn't realy a fly anymore after the encounter...
So you can even argue that the fly never goes to 0 km/h since at that moment she isn't a fly anymore.

Hahahahaha!

Brilliant reasoning, Observer, I wish I had thought of it! Big Grin
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08-09-2011, 03:57 PM
 
RE: Strange sum
OK, here is another:

Stand on an old-fashioned piano stool (with the axle well oiled), holding a bicycle wheel, each end of the axel between thumb and forefinger of one of your hands. Then give the wheel a rotation, by pushing on the spokes with the rest of your fingers. As the wheel turns, slowly tilt the axle to the vertical position.

What will happen?

Will the piano stool turn?

If yes, in what direction?
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08-09-2011, 04:22 PM
RE: Strange sum
The stool will turn in the opposite direction of the bicycle wheel. Inertia is the shit. Coolest force ever!

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08-09-2011, 04:48 PM
 
RE: Strange sum
(08-09-2011 04:22 PM)Stark Raving Wrote:  The stool will turn in the opposite direction of the bicycle wheel. Inertia is the shit. Coolest force ever!

Great answer, Stark!

As if the piano chair ‘thought’: “I must obey the Law of conservation of angular momentum. Since there is a sudden increase of angular momentum in one direction, I must compensate by turning in the opposite direction.”

OK, Here is another one, this time in math: how can you instantly calculate the square of any 2-digit number that ends with a 5? (like 15, 25, 35, etc,)
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08-09-2011, 08:16 PM
RE: Strange sum
Dammit, I'm not familiar with this one. I was gonna cheat and google it, but I'll try to savour the suspense and wait til someone knows the answer.

So many cats, so few good recipes.
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08-09-2011, 08:22 PM
 
RE: Strange sum
(08-09-2011 08:16 PM)Stark Raving Wrote:  Dammit, I'm not familiar with this one. I was gonna cheat and google it, but I'll try to savour the suspense and wait til someone knows the answer.

I will give you a hint:

(10x + 5)*(10x + 5) = 100x^2 + 100x + 25 = 100*x*(x+1) + 25
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