# Q & A: car acceleration

Q:
can you please explain the forces which make a car move.......since if only friction forces were responsible for accelerating the car then every car will have the same maximum acceleration that is ug ( mu * g) this makes BMW, FERRARI, PORSCHE all equal but indeed each car has different acc. ..........how to account for it.........thanks a lot
- luv (age 17)
india
A:
You're right that the acceleration would be limited to μg, and that this limit depends on the tires and the road, not the engine. When a car starts from rest, the initial power (Fv) is very low because velocity v is initially zero, so different cars start off with that same limit. However, once  the car has gotten moving, it requires a lot of power to accelerate  it more. The cars will all accelerate less than μg, and how much less will depend on how powerful the car is.

Mike W.

(published on 04/30/2009)

## Follow-Up #1: car acceleration

Q:
do you mean the maximum acc. possible on ground is ug...... but u is generally very less so ug will not be much...but some cars claim : 0-100 kmph in just 4-5 second.secondly how much power can be delivered due to streamlinig.Since good sports car like ferrari and all are to streamlined..thanks again
- luv (age 17)
india
A:
You're right that the maximum acceleration for some cars can be in the neighborhood of g,  9.8 m/s2. That means that the coefficient of friction, μ, has to be around 1 or so. (There's no rule that it can't be larger than 1.) According to the first sources I found via Google, the typical rubber-asphalt μ is about 0.8. So an acceleration of about 8 m/s2 is possible. That would give 0-100 kmph in about 3.5 s.

Mike W.

(published on 05/02/2009)

## Follow-Up #2: Air pressing down on car

Q:
Not so much a question, but it jot being mentioned annoys me slightly. There is gravity and the air puahing the vehicle down. IE formula 1 cars being able to drive on ceilings after achieveing a critical speed.
- Collin (age 28)
Nashville, tn, usa
A:

Good point. Once the car is going fast, it's pushing up on air so the air is pushing down on it.

Mike W.

(published on 11/18/2017)