According to newton's first law of motion:

"A body at rest stays at _________ and a body in motion stays in __________ unless an external _________ is applied."

The first law of motion states "A body at rest stays at rest and a body in motion stays in motion unless an external unbalanced force is applied."

In simple words, we can say that a body won't begin to move unless and until an outside force acts on it. When anything starts moving, it won't stop or vary its speed unless another force acts on it. It is also called as law of inertia.