Final answer:
When a rod in good electrical contact with poles can slide freely and is connected to a battery and a current, it will move downwards due to the motor effect.
Step-by-step explanation:
When a rod in good electrical contact with poles can slide freely, and the metal poles are connected to a battery and a current, the rod will move due to the interaction of the current and the magnetic field created by the battery. This is known as the motor effect, where a current-carrying conductor experiences a force when placed in a magnetic field. The direction of the force on the conductor is determined by the right-hand rule, which states that if you point your thumb in the direction of the current and curl your fingers, the direction of the magnetic field is the direction in which your fingers curl. In this case, the rod will move down.
According to Faraday's law of electromagnetic induction, a moving conductor in a magnetic field will experience an induced current, and as a result of the Lorentz force, the rod will begin to move. In this specific scenario, the rod is subject to a uniform magnetic field. The induced current will create a magnetic force on the rod that can cause it to move perpendicularly to both the magnetic field and the direction of the induced current.