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# Physics Behind Car Crashes

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on 16 October 2013

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#### Transcript of Physics Behind Car Crashes

Physics Behind Car Crashes
Topics
Newton's Laws of Motion

Momentum

Types of Collisions

Car Structure
Newton's Laws
Applies to every aspect of car accidents

Describes the motion of a body in response to forces acted upon it

The foundation of mechanics behind Physics

compiled by Isaac Newton in his Philosophiæ Naturalis Principia Mathematica
Momentum
Momentum = mass x velocity ( p = m x v )

Defined as the "quantity of motion" or "mass in motion"

A large amount of momentum can be created if an object has a large mass, high speed or a combination of both

A car with a large amount of momentum is dangerous as it will be very hard to stop
First Law of Motion: Inertia
an object either is at rest or moves at a constant velocity, unless acted upon by an external force.
Inertia: Strapped in seat belts
Since there is an unbalanced force acting on the car, it will not maintain its motion and will immediately decelerate to rest

The passenger will share the same state of motion as the car

The passenger and the car will decelerate as one body

The passenger will jerk forward
Inertia: Unstrapped seat belts
Due to the unbalanced force, the car will again abruptly decelerate to rest

The passenger will not share the same motion as the car

Due to Inertia the passenger will continue its state of motion

The passenger may exit the car and continue in projectile-motion depending on vehicle types
Second Law of Motion
Net Force = mass x acceleration

Without a seat belt the passenger would continue to follow Newton's first law of motion

Eventually the driver will come in contact with another object (windshield, dashboard)

The force that the driver hits that object is based off their mass and the acceleration of the car
Third Law of Motion
To every action force there is an equal and opposite reaction force.

Injuries in car accidents are a result of this law

Airbags are created to absorb the force that your body would apply on the dashboard or windshield in a car crash

Types of Collisions
Inelastic Collisions
Occurs when the momentum remains the same but the total kinetic energy changes before and after the collision

The two objects in the collision do not bounce away from each other

Momentum is conserved and total kinetic energy in not
Elastic Collisions
Occurs when both the momentum and total kinetic energy remains the same throughout the collision

The two objects in the collision "bounce" away from each other

Momentum and total kinetic energy are conserved
Car Metal Types
Cars made of harder metals crumple less, and the time taken for the car to come to a complete stop would decrease

As time decreases, rate of deceleration becomes greater

Since opposite force = mass x deceleration, the greater rate of deceleration would apply a greater force on passengers
Inelastic Collision Elastic Collision
In Conclusion...
Car accidents are a part of our every day lives and it is important to understand the physics behind it and how it can affect your body

Newtons law's apply in car accidents and not buckling your seat belts can lead to force being applied onto your body

Different forms of collisions exists

Heavier metals are more dangerous in comparison to a crushable design
Full transcript