Lecture Notes: The Science of Car Crashes

Introduction

• Presenter: Griff Jones, high school physics teacher.
• Location: Insurance Institute for Highway Safety's Vehicle Research Center.
• Focus: Understanding car crashes through physics laws.

Basic Physics Concepts

Inertia

• Definition: The resistance of any physical object to a change in its state of motion or rest.
• Example: A crash test dummy continues to move due to inertia until acted upon by an external force like a steering wheel.
• Newton's First Law: A body at rest remains at rest, and a body in motion remains in motion unless acted upon by an external force.

Momentum and Impulse

• Momentum (p): Product of an object's mass and velocity (p = mv).
• Impulse: Change in momentum, calculated as force applied over time (Impulse = Force x Time).
• Examples: Demonstrated using eggs thrown at a wall versus a sheet to illustrate different forces over different times.

Newton’s Second Law

• Formula: F = ma (Force equals mass times acceleration).
• Application: Explains the relationship between force and momentum in car crashes.

Acceleration and Deceleration

• Measured in g's: Fighter pilots and astronauts experience high g-forces.
• Application to crashes: High g-forces in a crash can lead to injury.

Car Crash Dynamics

Conservation of Momentum

• Newton's Third Law: Total momentum is conserved in a collision.
• Application: Head-on collisions and effects of different vehicle masses.
• Implications: Heavier vehicles can cause more severe deceleration in lighter vehicles during a crash.

Kinetic Energy in Crashes

• Kinetic Energy (KE): Depends on mass and velocity; KE = 1/2 mv².
• Importance of Speed: Doubling speed quadruples the kinetic energy.
• Energy Transfer: Rapid transfer in a crash causes injury.

Vehicle Safety Features

Crashworthiness

• Definition: The protection offered to occupants in a crash.
• Design: Includes crumple zones and safety cages to manage energy and protect occupants.

Structural Integrity

• Good Design: Crumple zones absorb impact, safety cage intact.
• Poor Design: Collapse of passenger compartment leads to high injury risk.

Advanced Safety Features

• Side-impact Airbags: Provide extra crush space and head protection.

Conclusion

• Importance of Understanding Physics: Vital for making informed decisions about car safety.
• Takeaway: Always wear seatbelts and understand the physics behind vehicle safety to reduce injury risk.
• Final Thought: The dynamics of car crashes are determined by the immutable laws of physics.