Newton's Laws of Motion

Newton's First Law (Law of Inertia)

• An object at rest remains at rest, and an object in motion remains in motion with constant velocity, unless acted upon by a net force.

Newton's Second Law

• A net force, $F_{net}$, acting on an object causes the object to accelerate.

• Equation form: $F_{net} = ma$

• If there is a net force, the object accelerates (velocity changes).

• If there is no net force, the object's velocity will not change (Newton's First Law).

• Can be applied separately in different directions: $F<em>{horizontal} = ma</em>{horizontal}$ and $F<em>{vertical} = ma</em>{vertical}$.

Newton's Third Law

• For every action, there is an equal and opposite reaction.

Problem Solving with Newton's Second Law

• To find acceleration ($a$) given force ($F$) and mass ($m$): $a = F/m$ (e.g., $50 N = 35 kg \times a \implies a = 1.43 m/s^2$).

• To find weight (force of gravity) ($F$) given mass ($m$): $F = mg$, where $g$ is the acceleration due to gravity ($\approx 9.8 m/s^2$) (e.g., $F = 10 kg \times 9.8 m/s^2 = 98 N$).