Why does it get warm in a car on cold day?

Solar Radiation: On a cold day, the sun's rays can still provide significant heat. When sunlight enters the car through its windows, it is absorbed by the car's interior surfaces, including the seats, dashboard, and floor. These surfaces then re-emit this absorbed heat, raising the temperature inside the car. This effect is often called "greenhouse effect" because the glass acts as a greenhouse, trapping solar heat inside the car.

Thermal Insulation: Cars are typically well-insulated to maintain comfortable interior temperatures. This insulation helps to prevent heat from escaping from the car, which can contribute to the build-up of warmth inside on a cold day.

Body Heat: Occupants of the car also contribute to the increase in temperature. Human body heat is constantly emitted, and when people are confined within the enclosed space of a car, their body heat accumulates, further raising the interior temperature.

Recirculating Air: Many cars have a climate control system that recirculates interior air to conserve heat and maintain a desired temperature. On a cold day, this system can trap the warm air generated inside the car, preventing the introduction of cold outside air and promoting further warming.

Engine Heat: In addition, the car's engine generates a considerable amount of heat while running. Some cars are designed to let residual engine heat circulate into the cabin, which can add to the car's interior warmth.

It's important to note that the exact rate of temperature increase and the overall warmth achieved inside the car can vary depending on several factors, such as the intensity of sunlight, the car's insulation properties, the number of occupants, and the efficiency of the climate control system.