Although the Army later adopted an algorithm for judging the hazard of an impulse based on the duration of the first positive pressure wave (A-duration) and the duration of the total acoustic event (B-duration), this algorithm did a poor job at predicting the hearing hazard of the large array of impulsive acoustic events to which people are exposed in the military and industry. At that time, the only way to get an accurate measure of the peak level of an impulse was to feed the microphone output into a storage oscilloscope, a process that was too laborious for routine industrial noise monitoring. Given the laborious process required for accurate measures of peak levels in the 1960s, this Army's decision was a wise one. This limit was copied from the Army Medical Department, which used the following logic: (1) some soldiers firing military rifles develop permanent threshold shift (PTS), (2) all military rifles generate peak levels in excess of 140 dB at the firer's ear, (3) therefore, earplugs must be worn whenever peak levels exceed 140 dB. Luz, in Encyclopedia of Environmental Health, 2011 Technology and Hearing Hazardous Noise RegulationĪs noted earlier, the US Walsh–Healy Act in 1969 imposed a limit on impulsive noise at 140 dB linear peak. (f) Safety glass - The windscreen glass is specifically designed to fracture into small rounded pieces upon impact instead of shattering so that the passengers will not be cut by the pieces that easily.G.A. The passengers will be protected from direct impact of external forces. (e) Passenger safety cell - The passenger safety cell is a strong rigid steel cage that will prevent the roof from collapsing on the passengers in the event that the car overturns. It prevents the wheels from locking when the brake is applied and held by the driver. (d) Anti-lock braking system (ABS) - The anti-lock braking system consists of a computerised system that rapidly holds and releases the brake alternately. (c) Side-impact bar - Strong metal steel bars inside the door frame provide passengers with extra protection in the event of a side impact. The passengers are prevented from being thrown forward due to their inertia. (b) Safety belts - The inertia-reel safety belts lock to keep wearers tightly held to their seats when a car decelerates rapidly. For safety protection by the air bags, the passengers must also be wearing safety belts at the same time. (a) Air bags - Air bags inflate within one hundredth second upon impact to cushion passengers from direct impact with the steering wheel, dashboard, or windscreen of the car. A good car safety that can prevent injuries to passengers in the event of an accident is of utmost importance. While striving to improve the performance of their cars, car manufactures also place great importance on the safety features of the cars. The hard surface gives a short impact time and a large impulsive force which can make the ball go far.ġ.
A golf club has a very hard hitting surfaces to give a big force on the golf ball. When the hammer knocks on a piece of metal placed on the anvil, the short impact time causes a large impulsive force to act on the metal.ģ. An anvil, which is made of steel, has a very hard surface. A blacksmith uses a heavy hammer and anvil to forge metals. The large impulsive force causes the spices to be crushed easily.Ģ. The impact time between the pestle and the mortar is very short because of their hard and rigid surfaces. The pestle is used to pound spices like chilli, onion and garlic. (c) The combined effect of the glove and the action of the hand prevents injury to the player.ġ. This action will lengthen the time of impact between the ball and the glove and further reduce the impulsive force acting on his palm. (b) When catching the ball, the player moves his hand backwards. (a) The glove which is made of soft material lengthens the time of impact and reduces the impulsice force acting on his palm. Figure 2.87 shows a baseball player stopping a fast moving ball with his hand. The loose sand lengthens the time of impact and reduces the impulsive force acting on him.ģ. A long jumper lands on a pit filled with loose sand. The impulsive force acting on the high jumper is reduced and he is less likely to suffer any injury.Ģ. When a high jumper falls on a mattress, the thick and soft mattress lengthens the time of impact. Increasing the time of impact, \(t\) to reduce the impulsive force, \(F\)ĭecreasing the time of impact, \(t\) to increase the impulsive force, Fġ.
0 kommentar(er)
