Final answer:
The strength of the magnetic fields inside the starter determines the force of a starter.
Step-by-step explanation:
The strength of the magnetic fields inside the starter determines the force of a starter. The force experienced by a wire carrying current in a magnetic field is given by the formula F = BILsinθ, where F is the force, B is the magnetic field strength, I is the current, L is the length of the wire, and θ is the angle between the wire and the magnetic field. Hence, the strength of the magnetic fields inside the starter determines the force experienced by the wire, which ultimately determines the force of the starter.