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Homework Help: Newton's Third Law Tire on Road Question

  1. Oct 31, 2009 #1
    1. The problem statement, all variables and given/known data

    I was reading a textbook that gave an example of Newton's Third Law using the explanation for every force there is an equal and opposite force. The example given was a car tire on the road being accelerated moving in the negative x direction. In the supplemental diagram (see image) there is a vector force horizontally from the tire as a result of the car being accelerated and the force of the road opposite the direction of motion. The book then goes on to state that the car actually moves the road but because of the mass of the earth its unnoticeable.

    My question isn't so much about the equal and opposite as it is where does the car touch the road so that it moves when being accelerated (i.e How can the car exert a force downward on the road when the car is being accelerated horizontally?).

    Does the tire have a tangential line of force in the negative x direction parallel to the road right where it touches the road?

  2. jcsd
  3. Oct 31, 2009 #2


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    , Think about what would happen if you were to accelerate from rest with your car tires on a very smooth icy surface. Or with your car on a lift with the tires suspended in air with no contact surface beneath, and your foot pressing on the acceleartor pedal. Would the car move forward? What horizontal force must be acting in order for it to accelerate forward?
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