AP Physics 1 Lecture: Dynamics

Introduction

• Presenter: Brian Brown
• Focus: Dynamics
• Review of concepts pertinent to the AP Physics 1 exam
• Topics: Forces, Free Body Diagrams, Newton’s Laws of Motion

Key Concepts

• Dynamics: Study of why objects accelerate or do not accelerate
• Forces: Interactions between two objects

Types of Forces

• Force of Gravity: Only field force, no physical contact needed
  • Equation: $F_g = mg$
  • Gravity constant $g = 9.8 \text{m/s}^2$, approximated as 10 near Earth’s surface
• Frictional Forces
  • Kinetic Friction: Occurs when an object is sliding
  • Static Friction: Occurs when an object is in contact but not sliding
  • Equation: $F_f = \mu \cdot F_n$
• Normal Force: Perpendicular to the surface
• Tension: Force along a string or rope, always pulls
• Spring Force: Can push or pull, depends on compression/stretch
  • Hooke’s Law: $F_s = kx$

Free Body Diagrams (FBD)

• Represent all forces acting on an object
• Draw forces as vectors, indicating direction and relative magnitude

Newton’s Laws of Motion

• First Law (Inertia): Objects remain at rest or in uniform motion unless acted upon by a net force
• Second Law: $F_{net} = ma$ (Net force equals mass times acceleration)
• Third Law: For every action, there is an equal and opposite reaction

Problem Solving

• Analyze whether an object is accelerating
• Use FBDs to identify forces and calculate net forces
• Apply Newton’s second law to solve for unknowns

Example Problems

• Multiple Choice: Approach with free body diagrams and system analysis
• Free Response: Analyze forces and derive expressions for quantities such as normal force and friction

Test-Taking Strategy

• Identify and list known forces
• Use consistent notation for forces
• Cross-check answers with physical intuition (e.g., direction of net force matches acceleration direction)

Conclusion

• Emphasize understanding of acceleration and force relationships
• Accurate representation of forces in FBDs is crucial
• Prepare for next session focusing on net forces in different motion types