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### Newton's Laws of Motion

• First law: an object continues in its state of rest or uniform motion unless an external force acts on it.
• Second law: the net force acting on an object is equal to the mass of the object times its acceleration: F = ma. The force F is in Newtons (N), the mass m is in kilograms (kg), and the acceleration is in m/s2.
• Third law, the law of action and reaction: If particle 1 exerts a force on particle 2, then particle 2 exerts an equal but opposite force on particle 1.
• The weight of an object is the force of gravity exerted on the object by the Earth. It has to be clearly distinguished from the mass.
• When an object moves on a rough surface, a frictional force always opposes the motion. If the object is stationary, a force of static friction acts on it with a magnitude that varies from zero to a maximum value.

## Newton's Laws of Motion

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