# Inertial Mass Propulsion? Feedback wanted. (1 Viewer)

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#### IMP

I have had this idea in my head for years and I want to know once and for all if it will work or not. I understand that a flywheel gains in mass when it spins. If this is true, is my thinking below correct? Any feedback would be appreciated!

Inertial Mass Propulsion:
I am going to try to describe a working model just to explain the concept that I have in mind: You have two flywheels on a common axis that can spin in opposite directions. Each flywheel has a motor/generator attached to it that can spin-up or stop the flywheels. Each of these motor/generators is connected together so they do not produce any torque. The flywheels can be spun-up or stopped at the exact same rate so the net effect is that no torque is produced (you could hold it in your hand during spin-up and not feel anything other than the gyroscopic effect when they were spinning). Hope you are with me so far.
You are floating in space (wearing your space suit of course) and you have this counter-rotating flywheel device with you. You attach a long length of strong extension cord to it. You have a battery pack with you that is capable of spinning up both of the flywheels to their maximum speed.
Here goes: You hold the device in your hands, activate the motors to spin-up the flywheels to their maximum speed, and you throw it away from you as hard as you can. Now, before the slack it taken up in the extension cord, you activate the generators to stop the flywheels and recharge the battery pack. When the assembly reaches the end of the extension cord, you pull it back to you. You push away from the device while the flywheels are spinning and pull it towards you when they are stopped. Push away from the device while it is “heavy” and pull it back while it is “light”.
So here is my question: would you start moving in the direction opposite the way you were throwing the device? Is the net effect “thrust”? Can you create mass, push away from it, and then convert the mass back to energy and the net effect be thrust?
Forget electrical losses and efficiencies etc, I am not concerned with that. I just want to know if it really works the way I perceive it. This means you could make thrust in any direction without giving up any mass (just giving up energy instead). Can this be?

#### berkeman

Mentor
IMP said:
I understand that a flywheel gains in mass when it spins.
Why do you say that? Do you mean at relativistic speeds?

#### IMP

I thought that a flywheel gains mass when it spins, and the faster it spins, the greater the gain. I am sure you have held a bicycle wheel by the axle in your hand while it is spinning. It sure feels "heavier" than when it is not spinning (or at least it resists changing directions). Could you push away from a spinning bicycle wheel with a greater result than pushing off of a non-spinning wheel?

#### berkeman

Mentor
I thought that a flywheel gains mass when it spins, and the faster it spins, the greater the gain.
Um, no. The flywheel does not gain mass as it spins faster. That is just the gyroscopic effect that you feel. The resistance is to changing the direction of the axis of rotation, not to linear translation motion.

The only time increasing the speed of something increases its mass is as you get close to the speed of light (c). The mass increases assymptotically (sp?) as you get closer and closer to c, the mass of the physical object goes to infinity. That's why you cannot accelerate an object to the speed of light or faster.

#### ZapperZ

Staff Emeritus
2018 Award
IMP said:
I thought that a flywheel gains mass when it spins, and the faster it spins, the greater the gain. I am sure you have held a bicycle wheel by the axle in your hand while it is spinning. It sure feels "heavier" than when it is not spinning (or at least it resists changing directions). Could you push away from a spinning bicycle wheel with a greater result than pushing off of a non-spinning wheel?
Er.. you may need to go back into your intro physics texts and figure this out. If a flywheel gains mass, classical mechanics would have been VERY strange. You are confusing the conservation of angular momentum, i.e. the resistance of the wheel to change direction, and mass.

You may need to learn and understand those basic principles first before coming up with some inertial propulsion.

Zz.

#### IMP

Well, since this is just theoretical anyway...
What if I could spin the flywheels very fast, say a couple million RPM's? Would they have artificial mass now? Say they are very small, maybe a millimeter in diameter. Say I can "cycle" them hundreds of times a second. Say I have a couple of million of these and each one is mounted on three-axis mounts so I can "aim" the thrust in any direction. Could I create thrust using energy only without actually lossing mass of my spacecraft?

#### IMP

OK, maybe it is not "artificial mass" that I am thinking of, but that invisible force that flywheels create. I have seen several videos on this site that are great examples of this force. Why can't you push away from that force, then stop the flywheel, bring it back to you, and the net effect be "thrust". It would seem that you would be going in the opposite direction from the way you pushed off when it was spinning.

#### berkeman

Mentor
The general concept that keeps you from being able to do what you are proposing is "the law of conservation of linear momentum". This law states that the total linear momentum of a closed system is a constant. So if you are on a frictionless plane or floating in a spacecraft, you and everything you are holding have a linear momentum (say a net of zero if you aren't moving at the moment). You cannot create a net movement from one place to another of yourself and what you are holding, because that would require you to have a net change in linear momentum (mass x velocity) for a period of time. You can throw an object in one direction to get yourself moving in the opposite direction, because the momentum of you and the thrown object together still equals zero -- you and the object have the same but oppositely directed linear momentum. That's how a rocket works -- it blows gasses out the nozzle, and that creates the oppositely directed force to accelerate the rocket. You could google conservation of momentum for more info.

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