Which of the following is an example of a non-contact force?

Gravity is a prime example of a non-contact force because it acts over a distance without any physical contact between the objects involved. Gravity attracts two masses toward each other, with the most familiar instance being the Earth pulling objects towards itself. This force operates even when the objects are separated by significant distances, demonstrating its nature as a non-contact interaction.

The other forces listed, such as friction, tension, and normal force, require physical contact between surfaces or objects to exist. Friction occurs at the interface of two surfaces in contact, resisting the relative motion between them. Tension is a force transmitted through a string, rope, or cable when it is pulled tight by forces acting from opposite ends and requires direct contact with the object to which it is attached. Similarly, normal force arises when an object is supported by a surface, acting perpendicular to that surface but only while they are in contact. Thus, gravity stands out as the only force in this context that operates without direct physical interaction, confirming it as a non-contact force.