Newton's First Law of Motion - Momentum and inertia
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Newton's First Law of Motion

Soccer
Kicking the ball illustrates
Newton's First Law of Motion

About 1000 AD, Ibn Sina came up with the idea that an object moving in a vacuum would just keep moving forever without slowing down. In the 1700s, Isaac Newton figured out a way to prove this was true using mathematics.

Newton's First Law of Motion tells us that

An object in motion tends to remain in motion, and an object at rest tends to remain at rest.

If you were out in space and you gave a rock a push, its momentum would keep the rock moving at the same speed in the same direction until it bumped into something. On the other hand, if you put a rock in space and left it there not moving, its inertia would keep it right there, hanging in space, forever (or until something bumped into it or it came under gravitational or magnetic pull).

On Earth, objects don't really remain in motion, because friction slows them down, and gravity pulls them toward the ground.

Bibliography and further reading about movement:

Gravity
Momentum
Friction
Physics
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Professor Carr

Karen Eva Carr, PhD.
Assoc. Professor Emerita, History
Portland State University

Professor Carr holds a B.A. with high honors from Cornell University in classics and archaeology, and her M.A. and PhD. from the University of Michigan in Classical Art and Archaeology. She has excavated in Scotland, Cyprus, Greece, Israel, and Tunisia, and she has been teaching history to university students for a very long time.

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