Crashes kinetic energy

The incidence of aircraft impacts may be significantly higher in certain areas (e g., in the vicinity or airports). The aircraft crash hazard is site specific and tlie failure is strongly dependent on the kinetic energy of tlie aircraft. Two types of data are needed to analyze for aircraft impact the aircraft crash rate in tlie site vicinity (per unit area per year) and tlie effective target area of tlie vulnerable item. Crash rates for different categories of aircraft can be obtained from state and national autliorities (e.g., FAA). The proximity of the site to airfields must be taken into account because crashes are much more frequent witliin a radius of approximately 3 miles. 

Two 800-kg cars moving at a velocity of 90 km/h have a head-on collision on a road. Both cars come to a complete rest after the crash. Assuming all the kinetic energy of cars is converted to thermal energy, determine the average temperature rise of the remains of the cars immediately after Ihe crash. Take the average specific heat of the cars to be 0.45 kJ/kg °C. 

If you take the same balloon and hold it under hot water for a period of time, the balloon s volume will increase. This happens because, as the helium atoms gain kinetic energy, they crash into the walls of the balloon faster, exerting more pressure on the inside of the balloon and causing it to expand. (You will learn much more about gases in Chapter 8.)... 

Imagine a pure liquid in a vacuum-sealed container. If we were to examine the space inside the container, above the liquid, we would find that it is not really a vacuum. Instead it would contain vapor molecules from the liquid. The liquid molecules are held in the liquid by intermolecular bonds. However, they contain a certain amount of kinetic energy, which depends upon the temperature. Some of the liquid molecules at the surface contain enough kinetic energy to break the intermolecular bonds that hold them in the liquid. These molecules launch themselves into the open space above the liquid. As the space fills with molecules, some of the molecules crash back into the liquid. When the rate of molecules leaving the liquid equals the rate of molecules entering the liquid, equilibrium has been established. At this point, the pressure created by the molecules in the open space is called the vapor pressure of the liquid. 

For example, if we raise a body and allow it to fall down, we would feel that due to the action of gravity the body will search a state where its energy is a minimum. However, here we are considering only the potential energy of the body. We will not take into account that the potential energy is meanwhile transformed into kinetic energy and that the floor where the body is coming at rest would warm up in the course of the crash. 

Bicycle helmets can be designed for impacts of up to lOOJ kinetic energy, their mass can be as low as 200 g and they are comfortable to wear. Helmets designed for much higher impact energy levels would be unacceptably large, so it is impossible to protect riders from the most extreme impacts. Compromises are necessary when designing to protect people, who have variable (and unknown) tolerances to impact acceleration, from crashes with variable circumstances. 

Practical tests of mobile crash beams with a friction arresting system have shown that the system works rehably, leading, in each case, to a safe dissipation of the kinetic energy and a safe arrest of the conveyance in the headframe. 

In crashes between different vehicle types differences in, mass and the protection that is offered are important considerations for the severity of the outcome. In a crash, the lightest party is at a disadvantage as it absorbs relatively more kinetic energy and because the vehicle generally offers less protection to an occupant than do heavier vehicles. This is also the reason why unprotected road users like pedestrians and cyclists, also called vulnerable road users, often sustain serious injuries. 

It is a key challenge for every traffic safety agency to establish a deep understanding of the critical factors in the road and traffic environment, vehicles and travel speeds that lead to the four most prevalent serious injury crash types. Then the challenge over time is to implement innovative and appropriate measures to take advantage of the opportunities to reduce kinetic energy exchange when crashes do occur. 

What do we know about kinetic energy, the (almost) universal direct cause of injury in a crash on the road We have known for more than three centuries—since Isaac Newton described the laws of motion in the seventeenth century—that the amount of kinetic energy generated by a moving object is a function of halfihe mass (the weight) of the object multiplied by the square (multiplying the number by itself) of its velocity (speed), so speed is far and away the key determinant of the amount of the force unleashed in a crash. 

Here are just a few of the myriad traffic safety examples of attempts to absorb kinetic energy as it is released in a crash before it impacts the body ... 

Similarly, side impact protection is quite limited the very small space between a vehicle occupant and side intrusion severely limits the vehicle designers options for absorbing kinetic energy before it impacts on the occupant. It is worth noting that the safety design rule for crash testing for side impact occupant protection requires a test at 50 km/h. Actual crashes at intersections on higher-speed roads often involve impact speeds well above this level. 

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