A force is needed between the tires of a car and the road in order for the car to turn. The force needed depends on three variables: 1) The force is directly proportional to the mass of the car. 2) The force is directly proportional to the car's speed squared. 3) The force is inversely proportional to the radius of the turn. Write a single equation relating force, mass, speed and radius based on the proportionalities given above.​