Relate friction and gravity to each of Newton's three laws of motion...examples
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I will write out each of Newton's laws of motion and handle each one individually:
1: A body at rest tends to stay at rest and a body in motion tends to stay in motion (in the absence of external forces). Gravity relates to this as a force acting on a falling object in a vacuum. Gravity is a constant force and as long as the falling object has enough airspace to continue falling it will continue to fall at a constant acceleration. Friction comes into play with wind resistance. The atmosphere will provide friction against a falling object in real life and will eventually halt the acceleration of gravity to a constant velocity (terminal velocity).
2: Force is equal to mass times acceleration (F=ma). Gravity is involved here as a regular constant force. Its acceleration is constant so it will act as a constant force on an object with any given constant mass. Friction is also a force against an object. But it will be a negative force against other forces since it is acting to deccelerate moving objects (negative acceleration times a mass equals a negative force).
3: For every action there is an equal and opposite reaction. Gravity is a constant force for every object resting against a surface (a book sitting on a table as an example). That means that since the book is exerting a force F on the table due to gravity, the table is exerting a force -F against the book. I do not see how friction really applies here.
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