Final answer:
Fields are a useful way to explain gravitational, magnetic, and electric forces because they allow us to describe how these forces act on distant objects without direct physical contact.
Step-by-step explanation:
Physicists use the concept of fields to explain gravitational, magnetic, and electric forces. A field is a property of space that is detectable by the forces it exerts. For example, the Sun produces a gravitational field that controls Earth's orbit, and stationary electric charges produce electric fields. Similarly, moving electric charges produce magnetic fields. Fields are a useful way to describe and understand these forces because they allow us to explain how they act on distant objects without direct physical contact.