# QuestionIs it possible to use mass movement inside a spacecraft to give acceleration using only onboard power?

#### Amigas

Consider a squash ball, when it hits the wall of the court the rubber compresses and the air inside also compresses causing the balls temperature to rise. This temperature rise is energy taken from the balls kinetic energy, causing the ball the hit the wall with less force.

Proof:
A ball of mass m
moving with velocity u in the negative x direction strikes the wall and rebounds with velocity v which is in the positive x direction with |v|<|u|. This change in velocity is acquired in very little time, meaning the force applied by wall is very large so the quantity of interest is impulse.
Initial velocity = −ui^ and final velocity = vi^.
So change in momentum of ball = Favgappliedbywallt=m(v+u)i^
By work energy theorem,
12m(v2−u2)=Heat lost to surroundings + Work done on ball
Work f=done on ball by wall is 0 as force is applied by wall on ball when the ball is in contact with the wall, so no displacement.
So, 12m(v2−u2)=
Heat lost to surroundings (1)
Case-[1]
From (1), we can see that if |v|<|u|
, more heat is lost.
And impulse imparted by wall is m(v+u)
Force applied by wall= m(v+ut
Case-[2] If |v|=|u|

Then from (1), 12m(v2−u2)=0=Heat lost to surroundings
Meaning no heat is lost (elastic collision).
Impulse imparted by wall is 2mu
So, force exerted by wall = 2muΔt
We can see that force applied by wall is greater in case (2) than in case (1).
And by Newton's Third Law, ball hits the wall harder in case (2) than in case (1).

So now consider a spacecraft, inside we have a magnetic projectile inside a cylindrical chamber.
We propel this projectile inside the craft using electromagnetic acceleration, the spacecraft moves in the opposite direction, at the other end of the chamber the projectile is stopped by it hitting the end stop, in this scenario we have a very slight displacement of the craft but no net acceleration.
However,
Now think about the squash ball, kinetic energy is lost due to the heating of the rubber ball, what if at the endstop we have coils of wire which allow current to flow due to electromagnetic induction.
Lenz law will cause the projectile to slow using some of the kinetic energy to be used in the electromagnetic induction process, causing a net loss in force at the endstop. In this scenario we have an imbalance in the closed system.

Some of the initial force we used to propel the projectile will be preserved. Hence we have a small net acceleration of the craft. We return the projectile to the start position, which is a net 0 acceleration.
We then repeat the process.

Could someone please point to where I have made my error in this idea.

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Particle Article

#### Phillip Huggan

The return to the starting position take energy. Now the projectile is starting from the bottom of the magnetic well when you power it up. With the B0 field on it will not rebound to the starting point. It is entirely possible to introduce energy into the system.
I like ethane and hydrogen to power ion engines. NASA has a concept to use solar-electric from Mars inward. You might shuttle batteries or propellant forward. About half of induction is lost by a counter-magnetic force that is akin to driving a car at low speed with the parking brake on. So your efficiency would need to be 150% or 133% or whatever for the perpetual motion to work. Radioactive fission plants seem like they would blow up in space.
Power beaming may be off assistance to you. You can potentially beam .5c or more on some wavelength using some technique. Zettl might find medical imaging, but at some velocity quantum effects happen that ruins some quantum laser systems. If you send stuff fast and the are entanglement effects you utilize, the system might not work at even .05c due to faster decoherence.
Perhaps you could store up potential energy by winding a shape change material that makes itself a flywheel. Zero point energy and stuff like it seem to require a GUT at least.

#### billslugg

There is an error in your idea. You assume that the internal mass is the only mass to lose kinetic energy due to heat dissipation. This dissipation of heat is exactly equally shared by the two masses. They each slow down by the same amount. The internal mass will rebound as will the cylinder. The process will be repeated at the other end and back and forth until all the kinetic energy of both masses is converted to heat. The center of mass of the system will never move relative to an external observer.

Helio

#### Amigas

There is an error in your idea. You assume that the internal mass is the only mass to lose kinetic energy due to heat dissipation. This dissipation of heat is exactly equally shared by the two masses. They each slow down by the same amount. The internal mass will rebound as will the cylinder. The process will be repeated at the other end and back and forth until all the kinetic energy of both masses is converted to heat. The center of mass of the system will never move relative to an external observer.
Sorry but I don't agree that the center of mass of the system will never move relative to and external observer.

If you have a mass internally in a craft in zero gravity environment any movement of this mass internally will cause a craft to experience equal force in the opposite direction, it must, newtons 3rd applies.

The internal mass is having a force applied with respect to the body of the craft.
The craft therefore must, experience equal force in the opposite direction, therefore from an external observers point of view, see movement.

Could you explain why the laws of motion do not apply in this case?

#### Amigas

The return to the starting position take energy. Now the projectile is starting from the bottom of the magnetic well when you power it up. With the B0 field on it will not rebound to the starting point. It is entirely possible to introduce energy into the system.
I like ethane and hydrogen to power ion engines. NASA has a concept to use solar-electric from Mars inward. You might shuttle batteries or propellant forward. About half of induction is lost by a counter-magnetic force that is akin to driving a car at low speed with the parking brake on. So your efficiency would need to be 150% or 133% or whatever for the perpetual motion to work. Radioactive fission plants seem like they would blow up in space.
Power beaming may be off assistance to you. You can potentially beam .5c or more on some wavelength using some technique. Zettl might find medical imaging, but at some velocity quantum effects happen that ruins some quantum laser systems. If you send stuff fast and the are entanglement effects you utilize, the system might not work at even .05c due to faster decoherence.
Perhaps you could store up potential energy by winding a shape change material that makes itself a flywheel. Zero point energy and stuff like it seem to require a GUT at least.
Sorry, I cannot understand a word you are saying.

#### billslugg

The center of mass of any isolated system can never move. This is a fundamental truth of science, it has never been proven wrong.
As your internal mass moves to one side, the external mass moves the same amount to the other side. This is Newton's Third Law in action.
Any external observer will see the external mass move to one side, pause, and then move exactly the same distance back where it started. No amount of internal damping or conversion to heat will change the end result of the total mass stopping at exactly the same spot it started.

#### Amigas

The center of mass of any isolated system can never move. This is a fundamental truth of science, it has never been proven wrong.
As your internal mass moves to one side, the external mass moves the same amount to the other side. This is Newton's Third Law in action.
Any external observer will see the external mass move to one side, pause, and then move exactly the same distance back where it started. No amount of internal damping or conversion to heat will change the end result of the total mass stopping at exactly the same spot it started.
Thanks makes sense.

#### Particle Article

we know hitting yourself does not cause retro or thrust movement, the blow is neither forwards nor backwards, then we could smash ourselves with a light thing very hard and and it would cause retro or thrust movement.
-- so how does this movement, which is none, anull in it's blow the movement linearly in one direction or the other the movement of weight which is consequentially a large weight which energy is not then anulled by the blow of stopping it which immediately does nothing propulsive? afaik as I know moving a weight and stopping it in a spacecraft leaves us moving

#### billslugg

Momentum is conserved. Both the weight and the spacehip gain and lose exactly the same amount at each bounce, and with opposite signs their momentums always add to zero. At each bounce some of the momentum is converted to heat. Eventually both the weight and the spacecraft come to rest at the same spot they started. You cannot permanently move a spacecraft by bouncing around inside. All spacecraft can only move by throwing mass out the rear end. In every case the center of mass of the that system never moves. When a spacecraft reaches the nearest star, its expelled gasses will be an equivalent distance x mass in the opposite direction.

Particle Article

#### Particle Article

yah- i know we do somehow thrust conserved mass. if rocket fuel is the paradigm, we also push on the atmosphere we have just created. My argument is that the bounce which is braking contact, it does nothing as far as far as propulsion or impellment, either backwards of forwards. Then we are left with the energy which was the movement of the weight of the beater, which does cause movement to our ship. This movement does not stop causing us to move forward when the braking contact is made, for simply striking ourselves does not cause us to move.

#### Helio

yah- i know we do somehow thrust conserved mass. if rocket fuel is the paradigm, we also push on the atmosphere we have just created. My argument is that the bounce which is braking contact, it does nothing as far as far as propulsion or impellment, either backwards of forwards. Then we are left with the energy which was the movement of the weight of the beater, which does cause movement to our ship. This movement does not stop causing us to move forward when the braking contact is made, for simply striking ourselves does not cause us to move.
Since heat can be considered to be in the form of photon, then like the rocket engine's thrust, the hotter wall would radiate those photons outside the box, producing a tiny acceleration, IMO. This wouldn't violate any physics laws, especially GR.

#### billslugg

Yes, you are correct. But in the case of a beam of EM radiation, the photons have momentum and mass. Photons have zero rest mass but have mass at the speed they are traveling. The space ship will lose some mass as it emits photons, this is no different than throwing matter out the back end. No laws are broken and we did not acellerate a spaceship wntirely from within.

Helio

#### Helio

Yes, you are correct. But in the case of a beam of EM radiation, the photons have momentum and mass. Photons have zero rest mass but have mass at the speed they are traveling. The space ship will lose some mass as it emits photons, this is no different than throwing matter out the back end. No laws are broken and we did not acellerate a spaceship wntirely from within.
Agreed.

#### Atlan0101

A spaceship will never lose more "light" energy than it acquires and absorbs from the universe. It may have exactly the opposite problem, acquiring and absorbing more light energy -- in various forms, too rapidly and in too high concentrations of dosages -- from the universe than it will ever lose in emission. If only we could have, gain, means to translate and convert that potential excess of universe provided energies (mass-energies) to useful purposes such as energy to energy to drive force, or energy to mass -- such as [matter | anti-matter] -- to energy to drive force.

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#### billslugg

How about using a solar cell to convert incoming light energy to electrical energy? It could be stored as chemical energy and used to propel an ion thruster.

#### Particle Article

@billslugg -
-converting light to a chemical has never been made possible

#### billslugg

I did not say we could convert light into a chemical. I said: "chemical energy". I was referring to charging a battery. Actually, light photons in the gamma ray region, totalling above 1.022 MeV can join to produce an electron and a positron. Similar processes can form any of the other particles, including protons and neutrons, so yes, light can be changed into chemicals.

#### Particle Article

@billslugg I did try to understand that one. Photosynthesis is part of this conjecture

powering ion thrusters isn't astonishing- their use is is a little more deficient for they demand chemical fuel as well as electricity

-quite simply we do need afaik turning electricity into accelerative movement

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#### billslugg

Yes, photosynthesis uses the energy from a photon of light to allow the joining of two chemical molecules (Carbon dioxide and water) to produce a new molecule (a sugar). No particle was created out of the photon, just the joining of two already existing molecules.

It is possible to join two photons to produce two new particles, an electron and a positron but that is only in the realm of high energy physics inside acellerators.

Ion propulsion is a very efficient method of acellerating a spacecraft, atoms are pushed out the back of the spacecraft at extremely high velocities, far higher than can be achieved with chemical propulsion.

Acelleration using a beam of light requires the use of no particles of matter, just a beam of light but the amount of push you get for a given amount of energy is fairly small. One Newton of force (about 100 grams) for the expenditure of 300 megawatts of power. If you have any mass to spare, you are much better off acellerating that mass to very close to the speed of light in a linear acellerator and then throwing it out the back of the spacecraft. Practically speaking, only the inert gasses are used as corrosion is a big problem.

Particle Article

#### Pogo

Internal reaction wheels can be used to rotate the ship or to maintain a required attitude, but no internal motion can be used to translate or accelerate the ship.

billslugg

#### Particle Article

@Pogo
-why?
you must concede that moving a weight inside a craft throws it in the opposite direction.
When this moment terminates- in space why would that motion stop?
When the movement stops, that hit doesn't send the ship retro, the hit has the same force both forwards and backwards. We cannot brake or move by hitting ourselves, leaving the forward motion of the weight active and unaffected by stopping the weight.
We could travel miles on this motion in frictionless space. But maybe we can draw the weight backwards slower than the speed we are moving at and repeat? I know it is considered that this doesn't work, but I can't see why not

#### Pogo

Let’s say when you throw the weight aft, it speeds up the craft in the direction of travel by 1 m/s. When it is caught by someone on the aft bulkhead, the catcher in contact with the aft bulkhead will absorb the kinetic energy thereby slowing the craft back to its original speed, conserving the energy of the craft and its contents. If it rebounds off the aft bulkhead instead of being caught, the craft would slow down a bit less the kinetic energy remaining in the thrown object, and so forth until the object comes to rest and the craft is at the same speed when this all started.

Particle Article

#### Particle Article

Thanks Pogo for trying to help me understand.
When the weight is caught by the aft termination
- I was thinking that that incident doesn't brake because the aft termination also knocks the weight forward the same,
in a similar way to trying to hit the bow to progress would not work
-like both objects contact nulls- each pushing the other doing nothing
-then the weight's impetus or inertia is the only thrust/retro force left in action
I don't quite get it, but ty!

Pogo

#### Pogo

An outside observe would see the spacecraft speed up slightly, then slow down slightly, then again in smaller increments until the thrown object ends up at rest. Then the final speed of the craft may be slightly slower due to any heating of the object if was in any way compressible. At any rate, the craft and anything inside could be considered a closed system requiring conservation of energy.

Particle Article