Final answer:
To increase the frictional force needed to prevent a car from skidding on a curved road, the car's speed should be increased.
Step-by-step explanation:
To increase the magnitude of the frictional force the road would need to exert on the car in order for the car to drive around the curve without skidding, the one change from the given options would be to increase the car's speed. Here's why:
- Increasing the car's speed would require greater centripetal force to keep the car moving in a circular path without slipping out of the curve. Since friction provides this force, a higher speed would necessitate a higher frictional force.
- Decreasing the car's speed would do the opposite, reducing the needed frictional force.
- Decreasing the curvature of the road (making it less sharp) would also lower the required frictional force, as the turn is easier to navigate at a given speed.
- Adding water to the road surface would decrease the available frictional force, as it reduces the friction coefficient between the tires and the road.
Therefore, to answer the question, increasing the car's speed is the correct option.