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  • Gasoline has approximately 56 Megajoules of chemical energy per liter , which is more

  • energy than you get from exploding the same of amount of TNT, and is enough to power a

  • toaster for a full day.

  • Cars work by burning gasoline to convert that chemical energy into the kinetic energy of

  • motion of the car, though almost 80% of it is lost as heat in the engine.

  • Still, 20% of 56 million joules is a lot of joules

  • To give a direct sense of gas-to-car conversion, it takes about five teaspoons of of gas to

  • accelerate a 2 ton car to 60kph, and about a third of a cup more for every additional

  • minute you want to keep it going at that speed.

  • That might not sound like a lot of fuel, but the energy of a car moving 60kph is equivalent

  • to dropping an elephantor stegosaurusfrom the top of a three-story building.

  • And in order for the car to stop, all that energy has to go somewhere.

  • If the brakes do the stopping, they dissipate the energy by heating up.

  • In the case of a collision, energy is dissipated by the bending and crumpling of metal in the

  • outer areas of the car.

  • And just like how smooth braking is nicer than a quick jerky stop, cars are carefully

  • designed to crumple - when they crash - in a way that lengthens the duration of the impact

  • so that stopping requires less intense acceleration.

  • Lots of acceleration over a very short time is not good for soft human brains and organs.

  • However, people don’t like driving cars with Pinocchio-length noses, so most cars

  • only have around 50 cm of crushable space in which to dissipate the energy equivalent

  • of our falling stegosaur.

  • That means that, while crumpling, they need to maintain a resistive force of about a quarter

  • the thrust of the space shuttle main engine.

  • Over half of the controlled-crumpling work is done by a pair of steel rails connecting

  • the front bumper to the body, which bend and deform to absorb energy and slow the car.

  • Most of the rest of the energy is absorbed by the deformation of other pieces of structural

  • metal throughout the front of the car.

  • This meticulously engineered destruction allows a crashing car to decelerate at a high but

  • reasonable rate: just slightly over the acceleration experienced by fighter pilots or astronauts

  • in centrifuge training.

  • As comparison, if cars were super rigid (like they were before the 1950s) and didn’t crumple,

  • they would stop so fast that they would undergo acceleration 15 times what fighter pilots

  • experience in training.

  • Thankfully engineers have learned to make cars with crunchy crumple zones surrounding

  • their rigid safety cell, because fully rigid cars are not good for fighter pilots or anyone

  • else.

  • Except, maybe, robots.

  • This MinutePhysics video was made possible by Ford - I was able to talk to an awesome

  • crash test safety engineer there who told me all about the complex physics and engineering

  • that goes into vehicle development and improving how cars perform in a crash.

  • Ford gave me this opportunity because they want you to know how important and carefully

  • designed all the parts involved are, and in particular that the only parts developed and

  • tested to work with their vehicles are original Ford parts.

  • If you want to learn more about why the right parts matter, you can head to takeagoodlook.com.

  • And I personally want to say that making this video has just reinforced to me that regardless

  • of what kind of car you have, big dents and deformations in the body aren’t just aesthetic

  • problemsthey can be safety hazards, too.

Gasoline has approximately 56 Megajoules of chemical energy per liter , which is more

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