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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.
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Suprisingly, the difficulty of driving backwards has almost nothing to do with the direction
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you’re facing and everything to do with the fact that you steer using the front wheels.
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When driving forwards, a car goes in the direction the front wheels are pointed. And when driving
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backwards, the car goes where the back wheels are pointed. Simple! But the difference is
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that going forwards, the direction of travel is determined by the same wheels you steer
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with, so you just point them where you want to go, and that’s where you go, the back
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wheels follow automatically. In physics, we call this a “stable” system, like dangling
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a pencil from your fingers – move your hand around and the pencil follows, no thought
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required.
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However, when driving backwards, the direction of travel is determined by the back wheels
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but you steer with the front wheels. So rather than just pointing the front wheels where
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you want to go, you have to point them in the direction that will get the BACK wheels
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to point in the direction you want to go – it’s an additional level of separation before the
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car does what you want. And in fact, if you don’t make any corrections, then over time
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the back wheels point farther and farther away from the direction you want to go: instead
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of following the front wheels, they want to run away!
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This is an unstable system, like trying to balance a pencil on your fingertip. It’s
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incredibly finicky and requires a ton of coordinated hand-eye feedback to maintain. That’s why
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you constantly have to readjust your steering when driving backwards – mathematically,
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your car is like an upside-down pencil!
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Of course, there are some successful rear-steering wheeled vehicles – forklifts, for example,
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drive only slowly and choose rear-steering for greater control of their forks.
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But let’s go in the other direction and add a TRAILER to your car – steering backwards
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has gained ANOTHER level of difficulty: you use your front wheels to get the back wheels
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to point in the direction needed to get the TRAILER to point in the direction you want
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to go. Not complicated enough? It becomes worse the more trailers you add – each one
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adds another level of separation between the direction of your steering and the actual
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direction of travel. Which is why it’s nearly impossible to push on one end of a chain or
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a rope and have the other end go where you want it to, and why you will never, ever balance
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a flexible rope or chain upright on your finger. Makes backwards driving seem downright easy!