Lecture on Linear Kinetics

Introduction to Kinetics

• Kinetics incorporates force into linear variables.
• Key Question: What does a scale read when standing in an upward-moving elevator?
  • The scale reads a higher value due to upward acceleration.
  • Kinetics explains why an object moves, focusing on forces and moments.

Key Concepts in Kinetics

• Kinetics: Study of forces and moments causing motion.
• Mechanics: Branch of physics studying body interaction and response to forces.
• Statics: Study of bodies not moving; focuses on balance of forces.
• Dynamics: Deals with moving bodies; forces cause movement.

Newton’s Laws of Motion

Newton's First Law (Law of Inertia)

• An object remains at constant motion or at rest unless acted upon by an external force.
• Inertia: Resistance to changes in motion, directly tied to mass.
  • More mass means more resistance.

Newton's Second Law

• Explains the relationship between force, mass, and acceleration.
  • Equation: F = ma (Force equals mass times acceleration).
  • Heavier objects require more force to accelerate.

Newton's Third Law

• For every action, there is an equal and opposite reaction.
  • When a body exerts force, it experiences an equal force in the opposite direction.

Free Body Diagrams

• Essential tool for understanding forces acting on a system.
• Example: Usain Bolt's foot during a sprint.
  • Draw forces like gravity, ground reaction, and muscular forces.

Force Data and Ground Reaction Forces

• Force plates measure how much force is exerted on the ground.
  • Measures in x, y, and z coordinates.
• Ground Reaction Forces (GRF): Equal and opposite forces exerted by the ground.

Internal vs. External Forces

• External Forces: Act outside the system (e.g., gravity, wind resistance).
• Internal Forces: Forces within the system (e.g., muscle contractions).

Applications and Examples

• Example with football linemen: Larger mass = higher inertia, less likely to be moved.
• Shot put and tennis ball: Demonstrate differences in mass and inertia.
• Free body diagrams simplify understanding complex force interactions.

Conclusion

• Today's lecture focused on principles of kinetics, Newton's laws, and their applications.
• Further exploration in labs and subsequent lectures.