Newton's Laws of Motion

Sir Isaac Newton's three laws of motion, published in 1687, form the foundation of classical mechanics. These laws describe the relationship between the motion of an object and the forces acting on it.

First Law - Law of Inertia

An object will remain at rest or in uniform motion in a straight line unless acted upon by an external force. This property is called inertia.

Mathematically, when no force acts:

∑F=0⇒dvdt=0\sum F = 0 \Rightarrow \frac{dv}{dt} = 0

where v is velocity and t is time

Second Law - Force and Acceleration

The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass.

F=maF = ma

where:

  • F is the net force (in Newtons)
  • m is mass (in kilograms)
  • a is acceleration (in meters per second squared)

Third Law - Action and Reaction

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

FAB=−FBAF_{AB} = -F_{BA}

where:

  • FAB is the force exerted by object A on object B
  • FBA is the force exerted by object B on object A

Applications in Classical Physics

Newton's laws are fundamental to understanding:

  • Planetary motion and gravitation
  • Projectile motion
  • Collisions and momentum conservation
  • Fluid dynamics and pressure
  • Gas behavior and kinetic theory