A whole magnet carries two different end types. Turn it around: the types trade places, but neither disappears.
Type one is left; type two is right.
Two practice carts, already let go. Switch the facing types, then change the gap. Matching types push apart. Different types pull together. Closer means stronger.
Matching types push; both carts move outward.
Do not turn the left practice magnet. Flip only the right one: its other end faces the gap, so the same two bars can switch direction.
Matching facing types: push apart.
Fresh mystery ends. X and Y pulled. Then Y and Z pushed. Y showed the same end both times. Now covered X faces covered Z.
FIRST X–Z TEST · BOTH ENDS STILL COVERED
Old records: X–Y pulled · Y–Z pushed · every type still covered
When the pins lift, will the untested mystery ends X and Z push apart, pull together, or can the old tests not tell us?
Lift both pins. Watch X and Z.
Slide right to the end.
