Presentation1 physics
- 1. The Physics Of Car CrashesF = M x ASmash!!KE = ½ x M x V2A = V/TP = F/A
- 2. Crumple ZonesThis was a major improvement from previous ideas about car safety. People thought that the tougher your car was, the safer the driver and passengers were. However, this idea was going against one major physics rule which is the faster you lose speed, the more deceleration you experience, therefore experiencing more G force:In 1952, Mercedes patented a design that meant that the front and rear of their cars ‘crumpled ‘ in an impact . This therefore slowed the deceleration that the drivers inside would experience. This would therefore reduce the deadly G forces that they would experience. This idea can be easily explained by this equation:Acceleration= Velocity/Time ThereforeIf you have a large velocity lost in a small amount of time:Acceleration=30ms/0.1 secondsThe acceleration will be very big:=300ms2As Force=Mass x Acceleration:If the weight of the person was equal to 75 kg and they experienced 300ms2 of deceleration, this would equal 22500/9.81=2293.6 kg of force, so therefore, this person experienced over 30.6 G! This could easily be fatal, as a human spine snaps at 21 G’s of force!
- 3. ContinuedIf the same car were to crash, but slow from 30ms in 0.5 seconds, then the driver would experience 60ms2 of deceleration.However, if there was a way in the car loosing its speed over a longer period of time, then the crash might not be fatal.If, once again, the driver’s weight is equal to 75kg x 60ms2= 4500N/9.81=458 kg of force. Therefore, the driver would experience just over 6.1 G! As fighter pilots, astronauts and Formula 1 drivers frequently experience this force, the crash would not be fatal, thanks to crumple zones.Woo! 6.1 G!
- 4. The first 3 point seat belt was put into production in 1959 by Volvo.Seatbelts And AirbagsThe first Air bag was designed in 1952, but wasn’t put into production until 1967!Both Seatbelts and Airbags follow the same basic rules of physics as crumple zones; If you make a mass slow down in a longer time, then it will not experience as much deceleration or G force and they would if it lost the speed in a very small amount of time.Acceleration= Velocity/TimeHowever, due to the large surface area of the air bag, the force that a person hits it at is spread over a large area and therefore the person suffers less injuries. The equation that explains this theory is:Pressure= Force/AreaAs Force= Mass x Acceleration, If a person with a mass equivalent to 75 kg and decelerating at 60ms2 = 4500N of force. Therefore, if this force is spread over a large area, such as an airbag, for example, 10m2, then using P=F/A = 4500/10, therefore, the pressure would be equal to 450 NM2. This is because, in a crash, seatbelts stretch and airbags inflate and cushion the persons face and body.
- 5. Side Impact BarsIn an impact, the bars create a larger surface area for the force, or energy obtained from the incoming vehicle to dissipate around, therefore, hopefully, imposing less on the people inside and keeping them safe:Pressure= Force/area. Side impact bars follow the same physics principals as that of air bags. This is because the bars themselves, usually reinforced steel bars, which are places into the sides of vehicles, including through the doors. (The green bars are the side impact bars)
- 6. SummaryThis energy ‘builds up’ when any object moves either by its self or is moved by something else. This energy is called ‘kinetic energy’, and we can work the amount of kinetic energy stored in an object by this equation;KE = ½ Mass x Velocity2There are many different types of modern crash technology, which all work in different ways and carry out different jobs. However, they all have one aspect in common; they are all trying to dissipate as much energy as possible. Finally, therefore, a bus weighing 6,000 kg travelling at 10 ms has the same KE as a car weighing 1500 kg travelling at 20 ms:For example, if a car has a mass of 1500 kg and is moving at 20 m/s, we calculate:½ x 1500 x 202 = 300,000 Joules
- 7. Ouch! But I'm OK thanks to my high tech crumple zone, seatbelt and air bag which all work together to increase the time it takes for me to lose my velocity, therefore decreasing the harmful G forces that I will experience, explained by the equation A= V/T and F = M x A. And also thanks to the car’s structure, including side impact bars, even in a frontal impact, and the cars airbags for dissipating the energy as quickly and as easily as possible, therefore reducing the possible harm on me from the accident due to the equation F = M x A and P = F/ASmash!!
- 8. EvidenceHowever, an old VW van with a very weak structure, no crumple zones, air bags and very simple seat belts don’t fulfil their task of keeping the occupants safe at 40 mph:A modern car (2009 Mercedes E class saloon) with top of the range crumple zones, air bags, energy dispersal bars and seat belts keep its driver and passengers safe and deals with the frontal crash at 40 mph, and the side impact tests at 31 mph, like this:http://www.youtube.com/watch?v=Yb0dvmRsH2c&feature=relatedhttp://www.youtube.com/watch?v=Ukq-UUQAcZs&feature=related