Newton's First Law of Motion (Law of Inertia)

1. What is Inertia?

• Inertia is the tendency of an object to resist any change in its motion.
• An object will:
  • Remain at rest if it is already at rest.
  • Continue moving in the same direction at a constant velocity unless acted on by an external force.
• Inertia depends on mass: The greater the mass, the greater the inertia.

2. Newton's First Law of Motion

• Statement:

  • An object will remain at rest or move at a constant velocity in a straight line unless acted upon by a net external force.

• Mathematical expression: $F_{\text{net}} = 0N \Rightarrow a = 0 \text{ m/s}^2$

  • If the net force is zero, there is no acceleration, and motion remains unchanged.

5. Key Takeaways

• Objects resist changes in motion due to inertia.
• Greater mass = greater inertia.
• Newton's First Law applies when the net force is zero.
• If a net force is applied, the object accelerates in the direction of the force.