Presentation on theme: "THE PHYSICS OF A CAR CRASH"— Presentation transcript:
1 THE PHYSICS OF A CAR CRASH Sam VentrescaCarla Marano
2 ScenarioA 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 hitsthe still car, creating an inelastic collision.3. Passenger of still car experiences whiplashand then comes to rest.
3 1. Moving Car Applies its Brake The brake pedal in a car is connected to a leverWhen you push down on the brake pedal (apply force), the lever multiplies this forceThis multiplication is necessary since your foot/leg would not be able to provide a great enough force to slow or stop the carSee illustration on next slide
4 Braking LeverThe 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 ForceThe 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-systemThese forms can consist of things like heat and soundIn 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 carsThis is referred to as an elastic collision, in which all energy is conservedIn real life, however, some of the kinetic energy will be lost to things like the sound of the cars strikingRegardless, momentum is always conserved!m1v1i + m2v2i = m1v1f + m2v2f
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 velocityThe 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 forceAlso known as inertia, this means that the passenger will stay at rest while his car moves forwardOnly 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 strainWithout a headrest, his body would be pushed forward while his head and neck stayed at restThus, his head would be bent far back, behind his seat, injuring his neck muscles and headThis is referred to as whiplash!After the car comes to a stop, this process will start again, but in reverseInstead, his head will want to continue at this velocity going backward, but the car will have stopped moving at this velocity alreadyThus, his head would snap forward, injuring the neck again
10 InsightThis 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 crashThe 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 headrestsWe 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
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