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
将一只大象 或者剑龙Σ(°Д°; 从三楼扔下来
to dropping an elephant – or stegosaurus – from the top of a three-story building.
而且 要使汽车停下来 那么这些能量就需要转移到别的地方 如果刹车的话
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
成耐形变的形态 当它们相撞时 这种设计加长了形变的时间
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.
但是 人们不喜欢带着匹诺曹的鼻子开车 所以大部分的车
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
这意味着 当车形变时 引擎周围的空间需要抵抗
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
缓冲器可以通过弯曲变形来吸收能量 使车减速 剩余的大部分能量
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
大一丢丢 相比较 如果汽车的车身炒鸡坚硬（就像在50年代以前）
in centrifuge training. As comparison, if cars were super rigid (like they were before
不会形变的话 它们会超级快的停下来 人们会获得
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
车身对飞行员或者其他人可不好 唔 机器人除外
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
problems – they can be safety hazards, too.