@janhardo With this simple change Maple2020 executes your worksheet without a problem.

I like your display of the magnetic field induced in the wire. Also, the 3D display is more enlightening that the 2D display.

@janhardo Thanks for your quick reply.

Unfortunately when I executed your downloaded worksheet only the opening text displayed. The commands producing the animation did not execute. I presume Maple2020 could not handle your implementation written in a later Maple version.

@dharr Thank you for explaining my programming error.

I moved the ode definition inside the MoveRod procedure and the animation worked perfectly

@dharr The Maple2020 help has given me a good understanding of this form of dsolve. Thank you.

@Rouben Rostamian  

@Rouben Rostamian  I downloaded your worksheet, made changes to adapt it to Maple2020, and executed it.

It is a beutiful answer to my question!

Obviously something is wrong in my question's downloaded worksheet in my interpretation into Maple2020 of the youtube's differential equations. Maybe I can determine my errors.

I deeply appreciate all of the answers you have sent me over the past few years. Thanks again.

@C_R These are interesting. They also solve the problem with a completely different math than in the youtube video reverenced in my worksheet.

I especially enjoyed the history of the problem outlined in the video included in one of your referrals.

@acer Rouben Rostamian's solution to a similar problem is very different from that in the referenced youtube video, but interesting none the less.

Can any other shape pass through a cube while removing more of the cube's volume?

@Kitonum Your procedure is the best way to generate any similar chain of tangent circles. Thank you for this.

@Rouben Rostamian  Thank you, Mr. Rostamian

@Kitonum Your answer implies that the formula in the cited book of the relationship between circle diameters as the key to forming the sequence of smaller, tangent circles can be replaced by your formula for the parabola, once the diameter of the original large circle is set. A wonderful discovery!

@Kitonum Thank you for discovering my error. I will try your finding with a few very different sized large circles.

@Rouben Rostamian  Once I feel familiar with the techniques you describe for the movable outer circle, I will have a go at solving the fixed outer circle solution.

@Rouben Rostamian  I will spend some time studying your replies in detail and will undoubtedly learn a great deal from you as always.

By the way. The first of the two problems, 12.25, stated that the larger circle is fixed to the line (or plane) on which it sits. Can your reply accommodate this fact?