# Overview of Newton's First Law of Motion

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• 0:01 A Classical Problem
• 0:58 The Idea of Inertia
• 1:50 Inertia at Work
• 2:25 The First Law in Practice
• 3:31 Lesson Summary

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Lesson Transcript
Instructor: Kevin Newton

Kevin has edited encyclopedias, taught middle and high school history, and has a master's degree in Islamic law.

Ever cursed the fact that your car wouldn't come to a stop as quickly as you might wish? Or, wonder how you get the dirt off your shoes when you kick them against a post? Well, wonder no more! Newton's first law of motion explains it all!

## A Classical Problem

Imagine for a moment the scientific understanding of the Ancient Greeks. While they got a great deal right, notably the idea of the atom, there were some things that they utterly missed. One of those is the idea of motion. According to the Ancient Greeks, all objects naturally seek a pre-designated location. Heavy items fall to the Earth quickly, since they are made of materials that come from the Earth, for example.

Obviously, this is not the case, or else so much of modern life would be impossible. Can you imagine the headlines: 'A Rocket Launch Fails Because the Metal in the Fuselage has Decided to Return to an Iron Mine?' Luckily, we have the benefit of Sir Isaac Newton's three laws of motion. In this lesson, we're going to look at his first law of motion, which states that an object in motion stay in motion, while an object at rest stays at rest until a force acts upon it. And no, the desires of the metal are not the types of forces we are talking about.

## The Idea of Inertia

Have you ever been driving someplace a little faster than you should have been? Go ahead, be honest. And chances are someone may have pulled out in front of you so you had to slam on the brakes. The car skidded, your passenger looked at you with a combination of annoyance and some uncertainty, but after a few feet the car comes to a stop. But wait! Didn't you hit the brakes back there?

Simply put, the car still had inertia. Inertia is the term given to an object's resistance to any change in motion. Your brakes changed your motion, but they did not do so with enough force to overcome inertia. That's probably not a bad thing, as had you not slowed down over at least some space, chances are that anything unsecured in the car would have inertia that the brakes couldn't stop.

## Inertia at Work

Inertia is a pretty powerful force, as anyone who has ever been thrown against their seatbelt can attest to. After all, it keeps the planets in orbit, helps cars maximize their energy output from engines, and carries long-distance runners the last few steps to the finish line. Inertia even helps you kick the dirt off your shoes. Really - when you kick your shoes against the frame to dust them off, the leather and sole of your shoe is firmly attached to your foot, so it doesn't go anywhere. Meanwhile, the dirt on your shoes is not so attached, so it flies off freely.

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