Newton's Laws of Motion

Introduction

• Part of Classical Physics, also known as Newtonian Mechanics.
• Time Period: 1642-1727.
• Kinematics: Study of motion (speed change, acceleration, distance covered).
• Dynamics of Motion: Understand the cause of motion and why a body moves or stops.

Key Concepts

1. Forces

• Definition: A cause that changes the state of an object.
• Unit: SI unit is Newton (N), CGS unit is Dyne.
• Type: Vector quantity (force has both magnitude and direction).

2. Types of Forces

• Contact Forces: Requires contact between objects.
  • Examples: Tension, normal reaction, spring force, friction force.
• Non-Contact Forces: Does not require contact between objects.
  • Examples: Gravitational force, electrostatic force, magnetic force.

3. Case Study

• Gravitational Force: Weight (mg) acts vertically downward, towards the center of the Earth.
• Normal Reaction: Perpendicular force exerted by a surface against an object in contact.
• Tension Force: Force exerted by a string or rope, always directed away from the object.
• Free Body Diagram (FBD): Visual representation of forces acting on an object.

Newton's First Law of Motion

• Statement: An object at rest stays at rest, and an object in motion stays in motion with a constant velocity unless acted upon by an external force.
• Implication: Describes the concept of equilibrium where net force is zero, leading to a state of rest or uniform motion.
• Inertia: The resistance of an object to change its state of motion.

Problem-Solving Strategies

Equilibrium Conditions

• Fnet = 0: The algebraic sum of forces acting on a body is zero.
• Breaking Forces: Analyze forces in horizontal (Fx) and vertical (Fy) components.

Inclined Planes

• Components of Weight: Along the incline (mg sin θ) and perpendicular to the incline (mg cos θ).

Example Problems

• Case 1: Simple vertical equilibrium with multiple masses and strings.
  • Solve for tensions in strings using equilibrium conditions.
• Case 2: System on an inclined plane with strings and pulleys.
  • Analyze forces, resolve into components, and apply equilibrium conditions.
• Case 3: Block over block problems.
  • Determine normal reaction forces between blocks and surfaces.

Additional Notes

• Vectors and Frames of Reference: Use appropriate frames to simplify problems.
• Newton's Laws in Advanced Problems: More complex scenarios involving acceleration will be covered under Newton's Second Law.

Conclusion

• Preview of Next Lecture: Newton's Second Law, spring forces, and their applications in more dynamic situations with acceleration involved.