# Is this really true or it's just science fiction?

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• 04-02-2002
shtarker
>> What would happen to the mole of petrol if you took it between differing gravities? ie earth to moon? Would the energy output change?

No.
In this case the energy derived is through breaking chemical bonds between atoms. A mole of petrol will always have a set number of molecules and therefore a set number of bonds to break.
Chemistry is soo much easier.
• 04-02-2002
Unregistered
E=mc^2 is not Einsteins equation.

The equation derived is E^2 = (mc^2)^2 + (pc)^2

If the observer and the object are in the same frame of reference (FoR) and both are stationary relative to each other then p=0, and the equation simplifies to the ever famous E=mc^2 (the negative solution be mathematically valid but physically unreal) which is the one generally used to calcuate things such as energy released in nuclear reactions since everthing is in same FoR and generally isn't moving anywhere.

More later if I can find my physics degree notes and textbooks on this subject (I think they may be unaccessable and at my parents house though).

As for Newtonian mechanics and particularly the kinetic energy of an object being 0.5*mv^2. This is the 1st order approximation of the above if you use the lorentz transform to substitute for the momentum and then one of the mathematical expansions to expand the series (I forget which one).
Newtons 3rd law and conversation of momentum and energy still apply for Trucks hitting bikes, bikes are worse off, they have less mass. Its only a simultaneous equation and can be reasonably approximate for the sake of why the biker dies as a perfectly elastic collision with solid non-deformable structures.

To be really confused consider electric and magnetic fields and how they change in different relativistic frames of reference.
• 04-02-2002
One of the early experiments to prove that time dilation did, in fact, occur was observing the half life for the decay of muons. Low energy muons poduced on Earth decayed at the expected rate, but high energy muons arriving from cosmic rays travelled a lot further, indicating that time was running slower for them.
• 04-02-2002
Nutshell
Your mass doesn't change no matter where u are, it's 'WEIGHT" that changes due to gravity.
• 04-02-2002
RobS
Quote:

Originally posted by Nutshell
Your mass doesn't change no matter where u are, it's 'WEIGHT" that changes due to gravity.
You forgot to add "Your inertial mass only changes due to how fast you're moving relative to a stationary frame of reference"

I also vaguely recall helping to explain this before, can't remember if it was these boards or the old ones though.
• 04-02-2002
Shiro
>Then e=mc^2 is not correct. As mass changes but energy can
>not. (provided the speed of light is independant of gravity)

Also energy can change. Note that also in classical mechanics that's a fact. If you take a stone and put it at some height, it has a certain amount of energy. If you take the stone heigher, it's energy increases.
• 04-02-2002
Matter and energy are two faces of the same thing, they can interchange. Think of matter as frozen energy.
• 04-02-2002
Procyon
Quote:

Originally posted by novacain
If I managed to get close to the speed of light and my mass increased. Would the mass of fuel I have also increase?
Thus the energy derived from the fuel increase proportionally to the energy needed to propel the ship?
That's essentially correct, at least as seen from the perspective of a nonaccelerating observer. Someone on Earth would notice that as your spaceship picks up mass it becomes more and more difficult to accelerate itself, and the rate of acceleration of the ship will drop as the ship approaches light speed.

(Actually, this only applies if you're being accelerated by an external energy source. For a ship carrying its own fuel there should be no difference; all the kinetic energy you acquire has to have been found inside the fuel originally.)

You'll see something quite different on the ship, though - you don't detect any increase in mass of your ship. However, as you approach light speed, the universe around you will seem to compress along the direction in which you're moving, allowing you to reach any destination easily within your lifetime if you can provide enough energy.
• 04-02-2002
sean
Well saying they'll be really old isn't accurate. It slows down time as you experience it. It's all in Einsteins theory of relativity. Just a relativity question: It is theoretically impossible to move faster than light. RElative to what? If two rays of light pass eachother, relative too the other one, the first will be travelling at 332,000 miles per second (600,000 km / second) - twice the speed of light. Is that a relativity loophole?
• 04-02-2002
novacain
>>Shiro: Also energy can change.

We were refering to the laws of themodynamics.

That is;
Energy in a system remains constant. It can not be created or destroyed and tends towards more random states.

but

if your mass increases as you approach the speed of light, does this not increase the available energy? (as available energy is mc^2)

>>shtaker: the energy derived is through breaking chemical bonds between atoms.
Doesn't the pressure and temprature at which a chemical reaction take place influence the energy output? (or only the speed of the reaction?)
I thought if the 'petrol' was on a planet with, say twice the gravity, the chemical bonds would have to be much stronger to form the 'petrol', thus releasing more when broken.
• 04-03-2002
shtarker
Quote:

>>Shiro: Also energy can change.

We were refering to the laws of themodynamics.

That is;
Energy in a system remains constant. It can not be created or destroyed and tends towards more random states.

but

if your mass increases as you approach the speed of light, does this not increase the available energy? (as available energy is mc^2)
<useless nitpicking>
The first law of thermodynamics is actually just a clarification of the law of the conservation of energy and really only applies to heat.
</useless nitpicking>

However the mass increase and extra energy associated with it comes from the energy released burning the fuel powering the rocket.

Quote:

>>shtaker: the energy derived is through breaking chemical bonds between atoms.
Doesn't the pressure and temprature at which a chemical reaction take place influence the energy output? (or only the speed of the reaction?)
I thought if the 'petrol' was on a planet with, say twice the gravity, the chemical bonds would have to be much stronger to form the 'petrol', thus releasing more when broken.
No.

The energy is derived from the petrol reacting with oxygen.
The principal behind this is relativly easy, energy is required to break a bond, while energy is used to form bonds.

A pratical example of this is disolving table salt in water. Sodium chloride is ionicly bonded (this is the most simple chemical bond between a metal and a non metal, where an electron is taken from the non-metal and given to the metal. They then have opposite charges so stick together) which means it has no real molecules, only a large ionic lattice. Therefore to dissolve it in water the strong ionic bonds holding this lattice together must be broken and replaced be much weaker bonds between sodium ions, chloride ions and water. As much more energy is required to pull the sodium and chloride ions apart, the energy to do so is taken from the water in the form of heat, hence adding as little as a teaspoon of salt to a cup of water can cause a drop in temprature of up to 5 degreease.

Temprature and pressure have nothing to do with the energy given off, they will just alter the rate.
And as for the rate alterting the energy out put, the number of atoms, and hence the amount of chemical energy stored in each bond, does not change no matter how fast the things react.
Finally gravity has no effect on the strength of the bonds. The strength is detirmined purely by the type of bond and the electronegativity of the atoms involved.
• 04-03-2002
novacain
So that petrol station on the moon is not as good idea as I thought.

shtaker:The first law of thermodynamics is actually just a clarification of the law of the conservation of energy and really only applies to heat.

And strangely money. As the world bank uses the laws of thermodynamics, applying them to world markets.
(unfortunately you can add more money to teh system by minting it)
• 04-03-2002
>>> Is that a relativity loophole?

No.

Relative to a hypothetical observer on one or other of the beams the other beam will be approaching at the speed of light.

Relative to a stationary observer, both beams will travel at the speed of light. If the beams are in opposite directions, then the effective speed at which they are approaching each other will be faster than light, but, and it's a big but, the speed at which they are approaching each other is an abstract concept, nothing physical is actually travelling faster than c.
• 04-03-2002
shtarker
>>And strangely money. As the world bank uses the laws of thermodynamics, applying them to world markets.
(unfortunately you can add more money to teh system by minting it)

No wonder I'm still poor, I've been looking at it in completly the wrong way
But I do remember reading some where about about a person (probbaby a really bored accountant) who worked through and tried to solve all the economic formulas and what not.
The end result, 1 = -1.
• 04-03-2002