Which force is defined as the force required to pull an object?

Tension force is the correct choice because it specifically refers to the pulling force that is transmitted through a string, rope, cable, or any other type of flexible connector. When an object is pulled, the tension in the connector or medium is what allows the force to be applied, effectively transmitting that force from one end to the other. It is particularly relevant in scenarios involving pulleys, lifts, or any system where a direct pull is necessary to maintain movement or convey force.

In contrast, frictional force acts in the opposite direction of movement, working to resist sliding or motion between surfaces, and is not responsible for pulling an object. Normal force refers to the perpendicular force exerted by a surface against an object resting on it, and is related to the weight of the object rather than pulling it. Air resistance force, also known as drag, acts against the motion of an object moving through the air, further opposing rather than contributing to a pulling action. Therefore, tension force is distinctly the force that describes the act of pulling an object.