Key Points from the Lecture on Falling Objects and Air Resistance

Introduction

• Question: Can a penny dropped from the Empire State Building kill someone?
• Objective: Test the myth with Adam Savage from MythBusters by dropping pennies from a helicopter on Derek.

Penny Drop Experiment

• Penny Weight: ~2.5 grams, less than a bullet.
• Height of Empire State Building: 443 meters.
• Expected Speed Without Air Resistance: ~300 km/h.
• MythBusters' Contraption: Used to test penny impact.
• Test Results: Pennies felt like small bullets but not fatal due to air resistance.

Air Resistance and Terminal Velocity

• Terminal Velocity: When gravity equals air resistance.
• Examples:
  • Hammer vs. Feather on Earth vs. Moon.
  • Terminal velocity impacted by object weight and air resistance.

Experiments and Observations

• Derek's Indoor Skydiving: Demonstrated terminal velocity with different objects.
• Felix Baumgartner's Jump: Achieved a terminal velocity over 1300 km/h.
• Raindrops and Hail:
  • Raindrops: Terminal velocity ~25 km/h, spherical shape when falling.
  • Hailstones: Potentially dangerous due to larger size and higher terminal velocity.

Penny's Terminal Velocity

• Pennies Stabilize Quickly: Reach terminal velocity after ~15 meters.
• Effect of Height: Same speed regardless of being dropped from 15 or 300 meters.

Aerodynamics and Projectiles

• Drag Coefficient: Influence of shape on air resistance.
• Bullet Shape: Modified from sphere to minimize drag.
• Ballpoint Pen Experiment: Tested potential danger, pens were not lethal.

Military and Historical Context

• Falling Projectiles in Warfare:
  • Fléchettes and Lazy Dogs used in past wars.
  • Modern military uses kinetic projectiles for precision.

Civilian Risks

• Deaths from Falling Objects: ~700 Americans per year.
• Energy Required to Fracture Skull: ~68 Joules.
• Notable Incidents: Measuring tape incident, potential dangers from heavy and aerodynamic objects.

Conclusion

• Penny Myth Busted: Pennies are not fatal when dropped from a height.
• Final Thoughts: Objects heavier than a few hundred grams with high terminal velocity can be dangerous.

Additional Resources

• Brilliant.org: Recommended for interactive STEM learning.