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THE PHYSICS OF A CAR CRASH Sam Ventresca Carla Marano.

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Presentation on theme: "THE PHYSICS OF A CAR CRASH Sam Ventresca Carla Marano."— Presentation transcript:

1 THE PHYSICS OF A CAR CRASH Sam Ventresca Carla Marano

2 Scenario A moving car rams into a stationary car. We will analyze the crash in the following chronological steps: 1. Moving car applies its brake. 2. Moving car’s velocity is too great and it hits the still car, creating an inelastic collision. 3. Passenger of still car experiences whiplash and then comes to rest.

3 1. Moving Car Applies its Brake The brake pedal in a car is connected to a lever – When you push down on the brake pedal (apply force), the lever multiplies this force – This multiplication is necessary since your foot/leg would not be able to provide a great enough force to slow or stop the car – See illustration on next slide

4 Braking Lever The lever has a fulcrum that is placed at two-thirds the distance of the lever towards the right side. This means that the length of the lever to the right of the fulcrum is half that of the left. When force is applied on either side, the multiplier is either double or half of the applied force since it must correspond to lever length and be equal on both sides

5 Brake Pedal and Force The physics concept that applies here is the impulse equation: F*Δt = m*Δv. – If a car with mass m changes its velocity, v, in a certain span of time, t, then an applied force must have been used to assist this change. So, the mass multiplied by the change in the velocity will be equal to the elapsed time multiplied by the force

6 2. Moving Car Strikes Stationary Car to Create an Inelastic Collision An inelastic collision is a collision of two objects in which energy is not fully conserved due to the transfer of kinetic energy to other forms outside of the two-car-system These forms can consist of things like heat and sound In the scenario of the car crash, the sound of the crash and the release of heat to the road or surrounding air are examples of lost kinetic energy

7 2. Moving Car Strikes Stationary Car to Create an Inelastic Collision (Con’.t) In an ideal collision, all kinetic energy remains within the system of the two cars This is referred to as an elastic collision, in which all energy is conserved In real life, however, some of the kinetic energy will be lost to things like the sound of the cars striking Regardless, momentum is always conserved! m 1 v 1i + m 2 v 2i = m 1 v 1f + m 2 v 2f

8 3. Passenger of Still Car Experiences Whiplash and then Comes to Rest. The velocity of the moving car will be transferred proportionally to the combined mass of the two cars into a new, lesser final velocity The passenger’s body will act according to Newton’s first law of motion, which states that the velocity of a body remains constant unless the body is acted upon by an external force Also known as inertia, this means that the passenger will stay at rest while his car moves forward Only the normal force of the seat will propel him forward with his car

9 3. Passenger of Still Car Experiences Whiplash and then Comes to Rest. In shock, the muscles in his neck will tighten and strain Without a headrest, his body would be pushed forward while his head and neck stayed at rest Thus, his head would be bent far back, behind his seat, injuring his neck muscles and head This is referred to as whiplash! After the car comes to a stop, this process will start again, but in reverse – Instead, his head will want to continue at this velocity going backward, but the car will have stopped moving at this velocity already Thus, his head would snap forward, injuring the neck again

10 Insight This project allowed us to take a deeper look into the physics behind certain aspects of car/car parts, as well as what exactly goes on during a car crash The lever application of car brakes was particularly new to us, as well as the scientific description of whiplash, which can be FATAL! As a result, the workings of car brakes are more clear, and we are able to see the necessity for headrests We also unintentionally dispelled the misconception that headrests keep your head stationary during a collision; they actually push your head forward so that it stays at the same velocity as the car

11 DRIVE SAFELY!

12 Works Cited parts/brakes/brake-types/brake1.htm sh1.jpg Whiplash%20Photo%202009/rachel2.JPG content/uploads/2010/04/iron-man-2-whiplash- figure.jpg?cb5e28 newton3laws.html


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