# what size frictional force would be needed for a car to go at a constant speed?

### 1 Answer

- 1 decade agoFavorite Answer
First, I'll assume the question is asking about a car going in a straight line (not changing direction at all), so the component of acceleration we are worried about is speed. According to Newton's Second Law of Motion, the sum of the external forces is equal to mass multiplied by the acceleration, or F = MA, right? Well, if the car is traveling at a constant speed, that means acceleration is zero, which means that the force (or sum of all the external forces) is also zero.

If the sum of the forces is zero, that means the frictional force would need to be exactly opposite to whatever other forces were acting, or, to put it more simply, the frictional force would need to be exactly the same "size" (magnitude is the proper word) as the forward-pushing force provided by the engine...

Source(s): College Physics