Solenoid operation

Generally, solenoids have a spring that pulls or pushes the plunger away from the center of the coil: >

COIL PLUNGER SPRING )))))))))=========ssssssss

In the diagram above, the tension spring exerts a force toward the right. When energized, the coil exerts a larger force, toward the left:

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Ok -- that makes sense, I think. Thanks. If the ferrite was instead a permanent magnet (ie. has it's own north and south pole) and I beefed up my example to have sufficient pull (like 500 amp-turns) as you have indicated -- would it then work that if I switched the direction of current in the coil that the magnet would move in opposite direction (as I would have changed the polarity of the coil magnet -- or would it still just pull to center)?

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Your basic assumptions are wrong. The handed rules do not apply. A ferrous object, iron,or steel will always move toward the highest flux concentration which is in the center of the coil, length wise. The handedness determines magnetic polarity, north or south but not attraction. Just as both ends of a permanent magnet, north or south will attract an iron object, so does a solenoid attract regardless of the polarity of the current. The nail should be sucked right into the coil if there is sufficient flux density to move it. Based on what you said, there is very little flux density in the coil and the iron barely moves but does show a little magnetic effect. It means you do not have sufficient magnetizing force or amp-turns per length to create much flux. To get a healthy pull on an object like a nail you may need about 500amp-turns or more in an inch or so of coil length. The higher the number, the more the force. Also, the greater the crosssectional area of the iron, the greater the force. A nail is a bit small, try a 1/4inch bolt. In fact, the iron sould fill the area in the center of the coil as much as possible but still move.

For example, a 14volt coil drawing about 300mA, the resistance would have to be 14/.3 = 47ohms. To get 500Amp-turns, the winding would have to be

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It might work if done right, however the forces on a permanent magnet are at right angles to the forces of attraction for a piece of unmagnetized iron. Most likely, a permanent magnet in a solenoid would filp around until in was "most happy" then it would stick to the side walls of the coil. Reversing polarity might flip it some other way. It's hard to analyze because the field lines and their interactions are very complex. It most certainly would not work like you want where it pulls in one way and pushes out on reversed polarity.

The voice coil on a loud speaker moves in the way you have described. Here the current, the magnetic flux and the resultant force are all at right angles to each other and a hand rule applies. When the current reverses, the force also reverses. It is possible but difficult to arrange a solenoid and permanent magnet to simulate this action but the magnet would have to be arranged so that its flux lines cross the coil at nearly right angles as it moves. The armature of a permanent magnet motor does this as it rotates. To generate linear motion, a voice coil is the best way to go, like a speaker. Bob