Which of these is an example of a non-contact force?

Gravity is indeed a prime example of a non-contact force because it acts at a distance without the need for physical contact between objects. It is the attractive force that pulls objects toward one another; Earth's gravity, for instance, pulls everything toward its center, which is evident through the phenomenon of weight. This force operates even if objects are far apart, demonstrating how non-contact forces function through fields, rather than direct interaction.

In contrast, friction, pushing a cart, and tension in a rope all require physical contact to occur. Friction occurs when two surfaces rub against each other, while pushing a cart involves direct physical contact between the person's hand and the cart. Tension in a rope is also a result of contact forces, as it relies on the physical connection between the rope and the objects it is connected to. Therefore, gravity stands out as the clear example of a non-contact force among the options provided.