The following applet simulated a front wheel drive car.
The engine provide power which drive the front tires rotate in the forward direction.
Due to friction force, front tires push ground backward,at the same time, ground push front tires forward. So the force on the front tires are in the forward direction.
However, the rear tires have to rotate with the front tires in the same rotation direction.
So the ground has to provide a back-ward push on the tire to make the rear tires rotate in the same direction as front tires.
If those two force are equal in magnitude but in oppositive direction, then, the net force on the car should be zero? Why the car can move forward?
What do you think about the above arguments? What is wrong? ???
Think about it. ::)
Use mouse to turn on [b]power[/b] check box, the car will star to move.
The drag force is assume to be in the form as Fb=-b*vx;
Red arrow shows the velocity. You can change the engine power with slider and turn on/off the power with checkbox.

Virtual Physics laboratory Original URL

Fu-Kwun Hwang, Dept. Of Physics, National Taiwan Normal University.