Name: Why is it Harder to Drive Backwards?
Uploaded: 2015-03-02T08:41:54.000Z
Duration: 3 min 25 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

When you turn a car’s steering wheel, the car follows a path along the same curve regardless

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whether you go forwards or backwards. So it seems like it should be just as easy to steer

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going backwards as going forwards. But clearly, it's not.

Suprisingly, the difficulty of driving backwards has almost nothing to do with the direction

you’re facing and everything to do with the fact that you steer using the front wheels.

When driving forwards, a car goes in the direction the front wheels are pointed. And when driving

backwards, the car goes where the back wheels are pointed. Simple! But the difference is

that going forwards, the direction of travel is determined by the same wheels you steer

with, so you just point them where you want to go, and that’s where you go, the back

wheels follow automatically. In physics, we call this a “stable” system, like dangling

a pencil from your fingers – move your hand around and the pencil follows, no thought

However, when driving backwards, the direction of travel is determined by the back wheels

but you steer with the front wheels. So rather than just pointing the front wheels where

you want to go, you have to point them in the direction that will get the BACK wheels

to point in the direction you want to go – it’s an additional level of separation before the

car does what you want. And in fact, if you don’t make any corrections, then over time

the back wheels point farther and farther away from the direction you want to go: instead

of following the front wheels, they want to run away!

This is an unstable system, like trying to balance a pencil on your fingertip. It’s

incredibly finicky and requires a ton of coordinated hand-eye feedback to maintain. That’s why

you constantly have to readjust your steering when driving backwards – mathematically,

Of course, there are some successful rear-steering wheeled vehicles – forklifts, for example,

drive only slowly and choose rear-steering for greater control of their forks.

But let’s go in the other direction and add a TRAILER to your car – steering backwards

has gained ANOTHER level of difficulty: you use your front wheels to get the back wheels

to point in the direction needed to get the TRAILER to point in the direction you want

to go. Not complicated enough? It becomes worse the more trailers you add – each one

adds another level of separation between the direction of your steering and the actual

direction of travel. Which is why it’s nearly impossible to push on one end of a chain or

a rope and have the other end go where you want it to, and why you will never, ever balance

a flexible rope or chain upright on your finger. Makes backwards driving seem downright easy!