Why are mountain roads generally made winding upwards rather than going straight up?
When talking about inclined planes, for a body going upwards, the force of friction is , where is the angle of inclination of a plane.
The force of friction is high if is small, and hence there is less chance of skidding.
The value of friction will be smaller for a road straight up the mountain since it will have a larger angle of inclination, and thus the chance of skidding will be more.