Why does friction point radially inwards when a car is turning in a circular path? When a car is turning along a circular path with a constant speed, it requires a centripetal force to keep it moving along that path. This force is a frictional force which points toward the center of the circle which the car traces. But why exactly does friction have to point radially towards the center? From my understanding, friction opposes the car's tangential motion, which means that friction should also be tangential but opposite to the velocity. I already understand that static friction will prevent the car from sliding along the path which its tangential velocity indicates, but I don't understand why the friction has to be perpendicular to the car. Please, if anyone knows, explain this using a vector diagram showing where exactly this perpendicular friction vector comes from. I would highly appreciate it! Thanks.
 A: 
This force is a frictional force which points toward the center of the
  circle which the car traces. But why exactly does friction have to
  point radially towards the center?

It points to the center because the centripetal force is needed to keep the vehicle on a circular path.

From my understanding, friction opposes the car's tangential motion,
  which means that friction should also be tangential but opposite to
  the velocity.

The centripetal friction does not oppose the car's tangential motion and is not, therefore, opposite to the velocity. That would be the case if, for example, when applying the brakes to a car moving in a straight line. The friction force of the brakes (and tires, if skidding occurs) opposes the direction of the vehicle causing it to decelerate, but the direction of motion is unchanged. 
When the car is on a circular path, the tangential velocity is constantly changing direction. To keep the car on a circular path the centripetal force continually acts perpendicular to the tangential velocity, pointing towards the center.

I already understand that static friction will prevent the car from
  sliding along the path which its tangential velocity indicates, but I
  don't understand why the friction has to be perpendicular to the car.

The force has to be perpendicular to the car in order to continually change the direction of the car to keep it on a circular path. Without it the car would travel a straight line due to Newton's first law which which tells us that and object in uniform motion in a straight line will continue to move in a straight line unless acting upon by an external force.

Please, if anyone knows, explain this using a vector diagram showing
  where exactly this perpendicular friction vector comes from.

See the diagram below. 
The green arrow shows the direction that the car would travel without the centripetal force due to its inertia. The red arrow shows the direction of the centripetal force acting on the car. The blue arrow shows the change in direction of the instantaneous velocity due to the centripetal force.
Hope this helps.

A: 
But why exactly does friction have to point radially towards the center?

Actually that's only the case if the car is traveling at a constant speed in a circular arc -- basically the object goes in a constant speed circle if and only if the acceleration is pointed straight at the center.  If the driver has their foot on the gas and maintains circular motion, then the net force will point ahead of the center; if the car is being allowed to slow down, then the net force will point behind center.

but I don't understand why the friction has to be perpendicular to the car

It doesn't have to be perpendicular to the car -- just to the line of motion.
Get on YouTube and watch videos of race cars going around corners for examples of cars that are turning around a center that's not on a line perpendicular to the car.
