Static Friction on a Turning Car

[IrishTwins]

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This hurts my head. Can anyone explain in kindergartener terms how to intuitively understand that the frictional force is static, and that it points towards the center?

 

[RogueUnicorn]

i don't know if it's intuitive, but remember that in all circular motion, the force has to point towards the center. that being said, what are the forces in a car, how does it move? it moves because the tires are spinning. why do spinning tires propel it forward? does a car in ice move? the answer of course is no, and therefore it must be friction that allows cars to move. finally then, we have to ask what kind of friction we are talking about. kinetic friction comes into play when you have objects sliding against each other. this only happens in cars when you're skidding out. thus, cars move by static friction between the tires and the road.* To think it in a different way, if you think of a spinning wheel, while the motion does go forward, you move through changing the surfaces in contact, through rotation, and not through sliding of any kind.


*Incidentally, this is the point of ABS brakes. Because cars move due to static friction, brakes are capped by the frictional properties of the tires and the road, and after this point, no amount of extra braking force will help you slow down any faster. So, ABS systems let you rotate the wheels at this maximum point so that you can maneuver the car without losing braking power.

 

[loveoforganic]

And static friction is generally larger than kinetic friction, so you also stop more quickly while retaining control

 

[ilovemcat]

i don't know if it's intuitive, but remember that in all circular motion, the force has to point towards the center. that being said, what are the forces in a car, how does it move? it moves because the tires are spinning. why do spinning tires propel it forward? does a car in ice move? the answer of course is no, and therefore it must be friction that allows cars to move. finally then, we have to ask what kind of friction we are talking about. kinetic friction comes into play when you have objects sliding against each other. this only happens in cars when you're skidding out. thus, cars move by static friction between the tires and the road.* To think it in a different way, if you think of a spinning wheel, while the motion does go forward, you move through changing the surfaces in contact, through rotation, and not through sliding of any kind.


*Incidentally, this is the point of ABS brakes. Because cars move due to static friction, brakes are capped by the frictional properties of the tires and the road, and after this point, no amount of extra braking force will help you slow down any faster. So, ABS systems let you rotate the wheels at this maximum point so that you can maneuver the car without losing braking power.

That's a really great explanation. Where were you 2 months ago when I was having trouble with this? 😛