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What is the direction of friction on the wheels of a 4-wheel drive?

What I thought was All the 4 wheels have a tendency to rotate such that vehicle goes forward. So friction acts backward.

However, in real life friction must act backward else the car won't stop.

Where am I wrong? Please explain.

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closed as unclear what you're asking by John Rennie, Jon Custer, Michael Seifert, user36790, heather Dec 15 '16 at 2:52

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • $\begingroup$ I think you wrote "backwards" twice by mistake. Also, it seems you talk about two different situations. Are you thinking of braking, normal driving or speeding up? $\endgroup$ – Steeven Dec 12 '16 at 18:11
  • $\begingroup$ ... And in real life if some external force (friction) does not act forwards then it won't start moving. $\endgroup$ – sammy gerbil Dec 12 '16 at 22:00
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When the car is speeding up , the wheels are rotating and have tendency to go backwards , hence the friction acts in the forward direction , giving a torque and acceleration. Without friction wheels wouldn't be able to rotate just as you wouldn't be able to sit in the car ! When brakes are applied , they stop start stopping the wheel , the wheel having a tendency to go forwards and hence the friction acts backwards hence stopping the car further. This is all right. But , I had once read when I was in 11th that when a car is accelerating friction acts in forward direction on 2 wheels (probably ,I had read the front ones) and in backwards direction on the other two. When I read this , it seemed contradictory. I don't know whether it was right or not but certainly , I had read this. If anyone could shed light on this too , it would be better.

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