Final answer:
Tires are considered unsafe for the operation of a vehicle when they are worn out and no longer have sufficient tread depth to provide adequate traction. In wet conditions, the presence of water reduces the friction between the tires and the road, making them more likely to slip. On ice, a low coefficient of friction between the tires and the road increases the chances of slipping.
Step-by-step explanation:
Tires are considered unsafe for the operation of a vehicle when they are worn out and no longer have sufficient tread depth to provide adequate traction. Tread depth is essential for maintaining grip on the road, especially in wet or icy conditions.
In the case of wet concrete, the tires will have less traction due to the presence of water on the surface. This reduces the friction between the tires and the road, making it easier for the tires to slip.
On ice, the tires are considered unsafe when the coefficient of friction (µ) between the tires and the ice is too low. A low coefficient of friction means that there is less grip between the tires and the road, increasing the chances of slipping.