# A centripetal force doubt

1. Aug 4, 2011

### jaumzaum

Hi everyone,

Maybe it could be an idiot question but I've never know why.

If centripetal force points to the center, Why a car making a turn tend to skid to away of the road? I mean, there would have to be a force opposite to centripetal, that is in fact, greater than it, for the resultant force to point outside. But if it were like that, how does the car have "force" to make its tangencial movement turn into a circular movement (thats the function of centripetal force).

2. Aug 4, 2011

### tiny-tim

hi jaumzaum!

https://www.physicsforums.com/library.php?do=view_item&itemid=529"is not the name of a separate force,

it is only the name given to whatever force is pulling towards the centre

for example, the tension in a string fixed to a peg is a centripetal force, and so in your case is the friction that stops the car skidding outward

if the car (going in a circle) suddenly hits a patch of ice, the reason it will start skidding sideways is because there is no force acting on it …

since acceleration = force/mass, a car can only continue in a circle if some force is giving it a https://www.physicsforums.com/library.php?do=view_item&itemid=27"

no force (beacuse of ice), no centripetal acceleration, so no circle

Last edited by a moderator: Apr 26, 2017
3. Aug 4, 2011

### PeterO

Even when the car skids, unless there is absolutely no friction, the car can achieve some form of circular motion, it is just that the radius of the circle is larger than the radius of curvature of the road.

You might consider the road to be two concentric circles, one of radius ,say, 100m and the other of radius 110m [ie the road is 10m wide overall. [for this example lets consider that the car is on the inside of the bend.

To continue round the corner, the inside of the car needs to maintain circular motion with radius 100m.

If the centripetal force available [resulting from friction on some carefully angled front wheels-you turned the steering wheel] can only maintain circular motion with radius 130m, the path will be that larger circle over-laying the road.

Relative to the road, the car will move further and further from the inside of the road, and eventually pass over the "outside" of the road - the car "spins out of control".