Issac Newton’s first law of motion is the law of inertia. It states that an object will remain at rest or in motion until an external force acts upon it.

What does this mean? Imagine that an object, such as a ball, is moving through space. How long will that ball continue to move? According to Newton’s First Law of Motion it will continue to move forever, unless something (an external force) acts on it.

Now imagine that the ball is at rest. How long will it stay at rest? Again, according to Newton’s First Law of Motion, it will stay at rest forever, unless an external force acts upon it.

So, what is this external force? It could be anything that causes the ball to change its velocity (or speed). For example, if you throw the ball up in the air, gravity will act upon it and cause it to fall back down to the ground. If you roll it along the ground it will encounter friction.

In summary, Newton’s First Law of Motion states that an object will remain at rest or in motion until an external force acts upon it. This is often referred to as the law of inertia.