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For every action there is an equal and opposite reaction. When we sit on a chair, our body exerts a downward force on the chair and the chair exerts an upward force on our body. If the chair didn't exert that force it would collapse under our body weight.

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An object will stay at rest unless acted on by a force. Objects can move forever without anything stopping them. The video states nothing will move without a push or a pull.

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This video talks about acceleration and briefly describes velocity. The woman demonstrates how to solve acceleration and how velocity ties into it. She demonstrates solving an example problem on how to calculate acceleration.

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Newton's first law of motion is described in this video. The video describes how friction plays a role in object's rest or motion. The video uses humor to describe the first law.

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Eratosthenes calculated the size of the earth 2,250 years ago on the Summer Solstice in Syene and Alexandria. He used basic geometry to come to his conclusion. His estimation was 15% different than the actual size of the Earth. This video draws out the components that went into the problem Eratosthenes solved in order to find the circumference of the Earth.

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