What is the anwser to this physics question?

Question

When your car moves along the highway at constant velocity, the net force on it is zero. Why, then, do you have to keep running your engine?

Answer 1

wind resistance , I think

Answer 2

Well, because the net force on it is NOT zero. (If it were, we'd all be surprised you were asking such a question!)

Wind provides a force. Separate from the wind, the air the car shoves aside requires energy be transferred from car to air molecules to perform the shoving. The road is not smooth and all those imperfections change the car's velocity angle back and forth (and usually it's velocity magnitude) and these are forces/accelerations. There is friction between the tires and the road surface which transfers energy from the car. (Like the air resistance, this can often be a magnitude change rather than both magnitude and angle change.) Gravity is drawing the car toward some point in the earth and the travel along the roadway requires continuing transverse acceleration. Movement of the car on its wheels (bouncing about, say, like one of those hydraulically adjustable cars on LA's streets) causes constant small shifts in the velocity due to the many accelerations.

All these forces/accelerations have to be resisted or "paid for" so to speak in order to continue on one's way. The energy required (and remember the inefficiencies in its production and use will make that value much higher than needed to overcome the actual causes) is what we continue to run the engine for.

Answer 3

Remember that forces impart acceleration, not velocity. This is undoubtedly one of the most common misconceptions in preliminary physics, along with Newton's third law. It took me a while myself to grasp the true concept of a force.

Since the net force on the car is 0, that means it is not accelerating either way. It is not speeding up or slowing down. So why do we have to continue running the engine? Because friction on the tires, axles, and wind resistance are all providing a force that is pushing against the car. That means those forces are trying to slow down the car. So if we want to continue at the same speed we have exert a force in the forward direction. That will ensure the net force is 0 and that you will not slow down.

Hopes this helps.

Answer 4

The force of the engine is the counter force to the other forces...gravity, wind, etc. When you combine these forces (add & subtract) you get a net force of zero.

If the net force were greater or less then zero your speed would be increasing or decreasing accordingly.

Answer 5

Wind resistance
Friction
Gravity
the transfer of Kinetic Energy to Potential Energy

Answer 6

The engine needs to overcome wind resistance and internal friction of engine and transmission.