What is Newton’s First Law of Motion?

Newton’s First Law of Motion

Hey Everyone! Welcome to this Mometrix video on Newton’s First Law of Motion.

Sir Isaac Newton began his discovery of this first law as he sat in his mother’s garden and witnessed an apple fall from a tree. He then started to formulate theories on why this might happen, and why things fall towards the center of the earth.

Well, Newton’s First Law of motion declares that, “an object will remain at rest or in uniform motion in a straight line unless acted upon by an external force.”
This is where we get the concept of inertia – where a physical object resists any change in its velocity; an object stays in its state of motion unless acted on by a force that changes that motion.

So, where do we see this law play out?

If you were to throw a ball out into space, the ball would keep going and going, and never stop, because there is no gravity in space; no friciton, and no air resistance working against the ball.

If you were to roll a ball on grass the ball would come to an eventual stop. In this setting the ball has friction from the grass, air resistance, and gravity working against it. The ball will also stop if it hits something, like a fence or a pole.

Let’s look at how we can more clearly see inertia play-out.

Imagine someone is driving in a car at 60 miles an hour, and then all of the sudden slam on their brakes. What happens? Well your car comes to a pretty quick stop, but your body flies forward. Why is that? Inertia! Your body wants to resist the change in velocity, and continue on how it was before. This is why we have airbags.

So, quick review. What does Newton’s First Law of motion (or Law of Inertia) state?
An object will remain at rest or in uniform motion in a straight line unless acted upon by an external force

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by Mometrix Test Preparation | Last Updated: July 3, 2020