Final answer:
The paper clip moves towards the magnet due to the magnetic force. Rubbing the paper clip with a magnet can magnetize it, causing it to exert a magnetic force on another paper clip. The more the magnetized paper clip is rubbed with the magnet, the stronger the magnetic effect becomes.
Step-by-step explanation:
When a paper clip moves towards a magnet lying on a table, the main force present is the magnetic force from the magnet attracting the ferromagnetic material of the paper clip. This force is attractive in nature. Additionally, there will be the gravitational force acting on the paper clip, but it is not significant in terms of the motion towards the magnet. If the paper clip is rubbed with a bar magnet, it may become magnetized itself, causing a force to act on a second, unmagnetized paper clip when they are brought close together. The force between two newly magnetized objects would be either attractive or repulsive, depending on their respective pole alignments.
If in the second step a paper clip, after being touched by the bar magnet, is brought close to another paper clip, the untouched paper clip will indeed experience a force which is typically attractive if the first paper clip has been magnetized and the poles are aligned oppositely. When the same paper clip is rubbed a few more times with the bar magnet, the magnetic effect increases, and the magnetic forces will likely be stronger. The paper clip that has been rubbed repeatedly can become magnetised, indicating that the domains within it are increasingly aligned in the direction of the magnetic field applied by the bar magnet.
At the level of their atoms and electrons, the magnetized paper clip has many of its microscopic magnetic domains aligned in one direction, whereas the unmagnetized paper clip has randomly oriented domains. When another object, like a knitting needle, is rubbed with a bar magnet and placed near the paper clips, it too can attract the paper clips if it becomes magnetized through the process.
The magnetic force between two conductors depends on their currents and the distance between them. According to the right-hand rule, one could determine the direction of the magnetic forces involved. Calculating the force between two parallel conductors involves considering the current, the length of the conductors, and the separation between them, as per Ampère's Law.