Newton's First Law

Physics

1. Fundamental Concepts

Definition: Newton's First Law, also known as the law of inertia, states that an object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
Inertia: The tendency of an object to resist changes in its state of motion.
Unbalanced Force: A force that results when the vector sum of all forces acting on an object is not zero.

2. Key Concepts

Basic Rule: $${\text{{If}}} \sum F = 0, {\text{{then}}} a = 0$$

Degree Preservation: An object will maintain its velocity if no net force acts upon it.

Application: Used to explain why objects continue moving or remain stationary without external influences.

3. Examples

Example 1 (Basic)

Problem: A book is lying on a table. What does Newton's First Law tell us about the book?

Step-by-Step Solution:

The book is at rest, so there are no unbalanced forces acting on it.
According to Newton's First Law, the book will remain at rest until an external force acts on it.

Validation: The book remains stationary because the forces of gravity and the normal force from the table cancel each other out.

Example 2 (Intermediate)

Problem: A hockey puck sliding on ice continues to move forward. Explain using Newton's First Law.

Step-by-Step Solution:

The puck is initially in motion.
Since the ice provides very little friction, there are no significant unbalanced forces to slow down the puck.
Therefore, the puck continues to move at a constant velocity.

Validation: The puck moves forward until it encounters a force like friction or a collision, which would change its motion.

4. Problem-Solving Techniques

Visual Strategy: Draw free-body diagrams to identify all forces acting on an object.
Error-Proofing: Always check if the sum of forces equals zero for objects at rest or in uniform motion.
Concept Reinforcement: Apply the principle of inertia to predict the behavior of objects under different conditions.