'Impossible' rocket drive works and could get to Moon in four hours

[Farmhand]

This is a very interesting thread, I could read this stuff all day.

I think some aspects kind of come back to "nothing is at rest in the Universe", wouldn't everything already have some momentum as well as inertia ?

We all on Earth are moving through space so we must have momentum.

As far as building vehicles that can carry people to other Galaxies and even to the outer reaches of our own, I'm not convinced it would be safe to power vehicles at high speed through space without some kind of protection from collision with objects ect. Great speed may overcome problems with time but introduce other problems.

We should remember there are different definitions for a "vacuum". I think the only true definition of the word vacuum on it's own is 2, a: in bold, unless a "partial vacuum" is specified or "the vacuum of space" is specified then - vacuum means "a space absolutely devoid of matter", when we are talking of deep space we are talking about a "partial vacuum" to some degree, surely. Aren't we ? The differences between 2,a: and 2,b: would be small but they would exist.

http://www.merriam-webster.com/dictionary/vacuum

Full Definition of VACUUM
1
:  emptiness of space

2
a :  a space absolutely devoid of matter
b :  a space partially exhausted (as to the highest degree possible) by artificial means (as an air pump)
c :  a degree of rarefaction below atmospheric pressure

3
a :  a state or condition resembling a vacuum :  void <the power vacuum in Indochina after the departure of the French — Norman Cousins>
b :  a state of isolation from outside influences <people who live in a vacuum...so that the world outside them is of no moment — W. S. Maugham>

4
:  a device creating or utilizing a partial vacuum; especially :  vacuum cleaner

..
Is it even possible to create a true vacuum ? I would be surprised if it is. Is this statement accurate ? In interstellar space, vacuums can approach 1 molecule per liter, which for all practical intents and purposes is perfect vacuum.

..

[MarkE]

@Mark E

Round and round we go indeed however I had to get off the merry-go-round a long time ago because it made me dizzy,lol.


I accept the fact a tangible force is required to accelerate any mass however I also accept the fact this accelerating force is resisted.... did Newton happen to mention the fact one force acting on a mass can only be resisted by another force?.


I have been down that road twisting and turning this way and that and I always ended right back where I started...go figure. Thus I choose not to participate in such things, as you say round and round.



AC

If you cannot measure one thing in the same units as a second thing that you claim the first thing is, then you have a tough row to hoe trying to establish that the first thing is actually the same as the second.

[Pirate88179]

This is a very interesting thread, I could read this stuff all day.

I think some aspects kind of come back to "nothing is at rest in the Universe", wouldn't everything already have some momentum as well as inertia ?

We all on Earth are moving through space so we must have momentum.

As far as building vehicles that can carry people to other Galaxies and even to the outer reaches of our own, I'm not convinced it would be safe to power vehicles at high speed through space without some kind of protection from collision with objects ect. Great speed may overcome problems with time but introduce other problems.

We should remember there are different definitions for a "vacuum". I think the only true definition of the word vacuum on it's own is 2, a: in bold, unless a "partial vacuum" is specified or "the vacuum of space" is specified then - vacuum means "a space absolutely devoid of matter", when we are talking of deep space we are talking about a "partial vacuum" to some degree, surely. Aren't we ? The differences between 2,a: and 2,b: would be small but they would exist.

http://www.merriam-webster.com/dictionary/vacuum


..
Is it even possible to create a true vacuum ? I would be surprised if it is. Is this statement accurate ? In interstellar space, vacuums can approach 1 molecule per liter, which for all practical intents and purposes is perfect vacuum.

..

This is why Dyson is building vacuums in space.  They are perfect...or nearly so. (Some would say they really suck)

Just kidding.

But seriously, I do not think there is anything in nature as a perfect vacuum, sort of like using the word instantaneous.  Neither exist but, some things get pretty close.

[gravityblock]

Actually integral calculus is very important to the example. The two separate actions of ejecting the two rocks under the conditions stipulated result in net changes of velocity: integrals of acceleration.  Had no rock been ejected, the boat would have had some position versus time profile in the reference frame.  Ejecting each rock alters the motion of the boat.  In the simplest case, the boat would have been initially stationary in the frame.  The momentum of either ejected rock in the reference frame and the ratios of the masses after the ejection determines the total change in velocity of the boat.  The boat's position integrates that change in velocity forever, as it does all subsequent changes in velocity.

No MarkE!  Here's a video demonstration since you apparently don't have the ability to properly visualize something in your head.  The first rock thrown determines the velocity's direction.  The second rock thrown in the opposite direction stops the motion of the boat, and the process repeats itself with a net motion.  Remember, in our hypothetical, the mass of the boat remains unchanged after the ejection of the rocks and there is no friction between the boat and the water.  It has nothing to do with the reduced mass of the boat after the rocks are thrown, nor does it have anything to do with the ratios of the masses after the ejection.  In other words, integral calculus doesn't apply in our hypothetical.  It's as simple as moving the boat 100ft. by throwing a rock, then stopping the boat by throwing a rock in the opposite direction, and then repeating the process over and over again.  Don't let the narrowness of your scope over complicate things by introducing ideas that have no relevancy to a particular case, such as integral calculus, which will cause an improper visualization.

Gravock

[MarkE]

No MarkE!  Here's a video demonstration since you apparently don't have the ability to properly visualize something in your head.  The first rock thrown determines the velocity's direction.  The second rock thrown in the opposite direction stops the motion of the boat, and the process repeats itself with a net motion.

IOW: The position is the integral of the velocity, just as I described.

Remember, in our hypothetical, the mass of the boat remains unchanged after the ejection of the rocks and there is no friction between the boat and the water.  It has nothing to do with the reduced mass of the boat after the rocks are thrown, nor does it have anything to do with the ratios of the masses after the ejection.

There you are absolutely wrong.  Let us use two examples:

Mass of the boat plus occupants:  100kg
Mass of each rock: 2kg
Ejection speed of the first rock with respect to the frame of reference:  10m/s
Case 1: Ejection speeed of the second rock with respect to the frame of reference: -10m/s
Case 2: Ejection speed of the second rock with respect to the boat: -10m/s
Initial condition:  Boat is at rest.

Eject first rock to the right, velocity change to the boat is: 10m/s * 2kg + V_{change_boat} * (100kg + 2kg) = 0  V_{change_boat} = -10m/s*2kg/(102kg)
Boat position now integrates at -0.19608 m/s.
Some time later the second rock is ejected.

Case 1: Rock is ejected left with respect to the frame of reference at -10m/s.
Velocity change to the boat is:  (-10m/s - V_start )* 2kg + V_{change_boat} * 100kg = 0  V_{change_boat} = (10m/s - 0.196m/s)*2kg/(100kg)
Boat position now integrates at -0.19608m/s + 9.804m/s * 2kg/100kg = 0.0.  The boat is stopped.  The first rock is moving rightward with respect to the frame of reference at the same speed that the second rock is moving leftward, the boat is at rest in the frame of reference and the net momentum sums to the initial value of zero.

Case 2: Rock is ejected left with respect to the boat at -10m/s.
Velocity change to the boat is:  -10m/s* 2kg + V_{change_boat} * 100kg = 0  V_{change_boat} = 10m/s*2kg/(100kg)
Boat position now integrates at -0.19608m/s + 10m/s * 2kg/100kg = 0.00392m/s.  The boat is drifting rightward.  The total momentum is:

-10.19608m/s*2kg + 0.00392m/s*100kg +10.0m/s*2kg = 0.0m/s*kg.  CoM is again satisfied and the boat position will integrate from the point that the second rock was thrown rightward at 0.00392m/s indefinitely.

If you had more rocks to start with you could repeat this process electing how hard you throw each propellant rock, and stepping the velocity accordingly.  If you started with 900kg of rocks instead of 4kg the initial velocity change magnitudes would be about 1/10th of the cases above and, the distance travelled in any interval would similarly be about 1/10th of the cases above.  Integral calculus absolutely applies.

  In other words, integral calculus doesn't apply in our hypothetical.  It's as simple as moving the boat 100ft. by throwing a rock, then stopping the boat by throwing a rock in the opposite direction, and then repeating the process over and over again.  Don't let the narrowness of your scope over complicate things by introducing ideas that have no relevancy to a particular case, such as integral calculus, which will cause an improper visualization.

Gravock

Doctor heal thyself.