Final answer:
A car's tires need more air in the winter because the lower temperatures cause the air inside the tires to contract, resulting in decreased pressure. It is necessary to add more air to maintain the optimal tire pressure recommended for cold tires by manufacturers.
Step-by-step explanation:
The winter, a car's tires need more air because the temperature is lower, so the air inside the tires contracts. Gases, including the air in car tires, follow the combined gas law, which describes the relationship between pressure, volume, and temperature. In cold conditions, the air molecules inside the tire move slower and take up less space, leading to reduced pressure. That's why you often need to add more air to the tires to maintain optimal pressure.
Manufacturers specify the optimal tire pressure for cold tires, assuming that the air temperature inside and outside the tire is roughly the same initial temperature before you drive. As when you drive a car, the friction between the tire and the road creates heat, which can cause the pressure inside the tire to rise because the air molecules move faster and collide more frequently. Hence, adding the right amount of air according to cold temperature ensures that the tires remain at the correct pressure when they heat up.