Question

During a summer day a scooter rider feels more comfortable while on the move than while at rest at a stop light because

• A. More heat is lost by convection while in motion
• B. Air is transparent to radiation, hence it is cooler than the body
• C. The object in motion captures less solar radiation
• D. Air has a low specific heat, hence it is cooler

Hint:

Forced Convection vs. Natural Convection: - Stationary state $\implies$ Natural Convection $\implies$ Low velocity $\implies$ Small $h$ value $\implies$ Poor heat dissipation. - Moving state $\implies$ Forced Convection $\implies$ High relative velocity $\implies$ Large $h$ value $\implies$ High heat dissipation rate.

Answer 1

The Correct Option is A

Picture the thin layer of warm, moist air that clings to the skin. When the rider is standing still at the signal, this air film barely gets disturbed, so it keeps warming up and becomes nearly saturated, which makes it harder for fresh heat and sweat to leave the body. Once the scooter starts moving, the oncoming wind constantly sweeps this warm film away and replaces it with cooler, drier air, so both convective heat loss and sweat evaporation speed up a lot. This constant renewal of air right at the skin, driven purely by the vehicle's own motion, is forced convection, and it carries heat away far more effectively than the sluggish natural convection that happens when the rider is stationary. That is exactly why the rider feels comfortable while riding and warm while waiting at the stop, confirming option 1.