To a physicist, 'acceleration' includes a change in speed or direction. Look up wikipedia to get a more thorough picture. This is the same acceleration in F=ma so it's crucial that we use a consistent definition.

I have a clear understanding of that , and physicist also use decelerate to describe using a force to decelerate a object.

picking at straws are we?

Is this how it works?:

1. Accelerate the mass, starts moving the pipe.
2. Turn it around, applies a force the wrong way.
3. Turn around again, applies the same force the opposite way.
4. Repeat.

The two turn-arounds cancel each other out. Leaving only the acceleration to propel the pipe?

but closer to

1. accelerate 20 masses applies 20 positive forces.
2. turn 1 mass around 180 degrees applies a negative force.
3. turn 1 mass around 180 degrees applies a positive force.
4. the 20 opposing masses are free floating applies zero force negative or positive.

5. repeat.

the result of this is constant acceleration of the pipe

even after the pipe has traveled the lenght of the pipe.

or the lenght of a billion pipes or a trilion pipes

as long as you have the electricity to supply an

acceleration to the 20 masses.

3/4 inch of dust build up on the moon in 4.527 billion years,LOL and QM is fantasy science.