Newton's first law, often called the law of inertia, states that an object at rest will stay at rest, and an object in motion will stay in motion with the same speed and direction unless acted upon by an unbalanced force.

It's important to understand how this law applies to a falling object:

* The object is not truly at rest. Even though it might appear motionless before falling, it's actually being acted upon by the force of gravity. This force is constantly pulling the object downwards, even when it's seemingly "at rest".

* The unbalanced force is gravity. The force of gravity is the force that pulls the object downwards. This unbalanced force causes the object to accelerate.

* The object's motion changes. Because of gravity, the object's state of motion changes. It starts at rest and then accelerates downwards. This change in motion is a direct result of the unbalanced force acting on it.

So, while Newton's first law states that an object at rest stays at rest, this is only true if there are no unbalanced forces acting on it. In the case of a falling object, gravity is the unbalanced force that causes the object to accelerate downwards.

Here's a simple analogy: imagine a book on a table. It's at rest. Newton's first law tells us that it will stay at rest unless acted upon by a force. This is true, but only if there are no other forces acting on it. If you push the book, you apply a force and it starts moving. Similarly, the force of gravity acting on the book when it's on the table is balanced by the upward force of the table. When you remove the table, gravity becomes the unbalanced force, causing the book to fall.