# Physics with Calculus/Mechanics/Newton's Laws

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**Newton's laws** describe what causes motion of objects. There are three laws, which can be briefly stated:

- First law: In an inertial reference frame, unless acted on by a net force, an object at rest stays at rest.
- Second law: In an inertial reference frame, force is equal to mass times acceleration ()
- Third law: For every force, there is an equal and opposite reaction force ()

Each of these laws will be discussed in more detail in each section.