When a car moves along the highway at constant velocity, the net force on it is zero.?

When a car moves along the highway at constant velocity, the net force on it is zero.? Why,then, do you continue running ur engine?

 

Answer

Wind resistance and friction with the road are trying to slow you down. This is a force and it's not zero. Your engine can oppose this force with an equal and opposite force. Take your foot off the gas or somehow remove all resistance and the car will either speed up or slow down. The opposing forces will no longer cancel out. This sum of opposing forces is called net force.