Important Rules:

If an object is in "equilibrium" - it does not move at all, or the object has a constant velocity - acceleration is zero.
The standard unit for force is Newton [N]. $LaTeX: N=\frac{kg\cdot m}{s^2}$

Common Forces Encountered in Newton's Law Problems

Normal Force
- Always perpendicular to the surface of an object is resting on
- If an object is suspended in the air by a cord/string/rope, there is NO normal force.
Tension
- The tension originates at the point of contact and comes out of the object, pointing along the string.
- When the mass of the string is ignored, the tension is the same on either end of the string.
Gravitational Force
- Always points down to the ground.
Friction Force
- Opposes or impedes motion.
- If an object is static (not moving), use the static friction formula (f_s)
- If an object is kinetic (moving), use the kinetic friction formula (f_k)

Equations

$LaTeX: {\boxed{Newton's\ Law:\ Static\ or\ Constant\ Velocity}}$

$LaTeX: \sum\overset{\rightharpoonup}{F}=m\overset{\rightharpoonup}{a}\\ \sum{F_x} = 0 \\ \sum {F_y} = 0 \\$

$LaTeX: {\boxed{Newton's\ Law:\ Accelerating\ Object}}$

$LaTeX: \sum\overset{\rightharpoonup}{F}=m\overset{\rightharpoonup}{a}\\ \sum{F_x} = ma_x \\ \sum {F_y} = ma_y \\$

$LaTeX: {\boxed{Friction\ Equations}}$

$LaTeX: f_s\le \mu _sn\\ f_k=\mu _kn$