# Physics with Calculus/Mechanics/Newton's Laws

• Second law: In an inertial reference frame, force is equal to mass times acceleration (${\displaystyle {\vec {F}}=m{\vec {a}}}$)
• Third law: For every force, there is an equal and opposite reaction force (${\displaystyle {\vec {F}}_{\mathrm {a} b}=-{\vec {F}}_{\mathrm {b} a}}$)