A bar magnet moves a paperclip without touching it. This is an example of a non-contact force because the magnet is able to exert a force on the paperclip without any physical contact between the two objects. The force between the magnet and the paperclip is called magnetic force.

Explanation:
Non-contact forces are forces that can act on objects without any physical contact between them. These forces can have a significant impact on the objects involved and can cause them to move or change their shape. One example of a non-contact force is the magnetic force.

The magnetic force is a force exerted by magnets or magnetic materials on other magnets or magnetic materials. It is responsible for the interaction between magnets and can cause them to attract or repel each other.

In the given example, the bar magnet is able to move the paperclip without touching it. This is because the magnet produces a magnetic field around it. When the paperclip is brought close to the magnet, it experiences a magnetic force due to the interaction between the magnetic field of the magnet and the magnetic properties of the paperclip.

The magnetic force between the magnet and the paperclip is strong enough to overcome the force of gravity acting on the paperclip, causing it to move towards the magnet. This demonstrates how a non-contact force, in this case, the magnetic force, can act on an object without any physical contact.

In contrast, the other options listed in the question involve forces that require physical contact between objects. For example, in option b, the toy car slides down the ramp due to the force of gravity acting on it. In option c, the child lifts the book by applying an upward force on it. And in option d, the marble slows down on the carpet due to the frictional force between the marble and the carpet.

Therefore, option a, where a bar magnet moves a paperclip without touching it, is the correct example of a non-contact force.