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START YOUR JOURNEY - LAWS OF MOTION

Newton’s Laws of Motion Challenge

 You chose : 1. The Law of Inertia: “An object at rest tends to stay at rest and an object in motion tends to stay in motion.”

This choice is not the right one for the example.

However, it still applies to rocket flight! It’s easiest to see how Newton's First Law works when the rocket gets above the Earth’s atmosphere (to avoid air resistance).

Because there is very little friction in orbit, when a satellite is “in motion” it will stay “in motion,” orbiting the Earth continually just as Newton predicted…until something (a force, such as a rocket motor) comes along to change that condition.

There are some residual air molecules up where the satellites orbit, so they do encounter very slight air resistance, which can eventually slow them down (it takes many years). We call this “orbital decay.” Rocket boosters on a satellite can correct the decay from time to time. Otherwise, the satellite must be repositioned.

Newton's First Law is also valid on Earth. However, on the surface of the planet, air resistance is present and slows a moving object. To counter air resistance, a continuous forward force must be applied.

For example, automobiles must constantly run their engines in order to maintain a forward movement. An automobile has additional friction from the wheels, wheel bearings, and the road. The sole purpose of running the automobile engine continuously is to overcome all the different friction sources. Otherwise, a small push would keep an automobile moving forever. (Hills and valleys present special situations…but that’s another story.)

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