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 elephant – or stegosaurus – from 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

problems – they can be safety hazards, too.