While travelling by train, when the train passes through the tunnel, why does our earache?
A. Atmospheric pressure
B. Tunnel pressure
C. Water pressure
D. None of the above

Hint: When a train passes through a tunnel, low air pressure is created inside due to the train's high speed. Our middle ear pressure is still preserved at its original level, resulting in an unbalanced state of middle ear and canal sound pressure, as well as the eardrum bulging process.

Complete answer:
When a train enters a tunnel, it acts like a piston, compressing the air in front of it. The air in a tunnel, unlike outside air, cannot simply be pushed aside since the tunnel walls are in the way. Some of the air is forced forward, all the way to the opposite end of the tunnel, but the majority of it rushes through the tight space between the train and the tunnel walls, filling in the space behind the locomotive.

The air rushes quicker as it is squeezed into this small space, similar to how water speeds up at the bottom of a funnel. In fact, the tunnel air can surge backwards at a far greater rate than the train can move ahead. His fast-moving air creates a vacuum within the train, reducing the air pressure and making your ears pop. It makes your ears hurt. Hence, because of sudden increase and decrease in pressure inside the tunnel, our ear aches.

Thus, the correct option is option B.

Note: Bernoulli's principle states that the faster air flows, the lower the pressure. Many people are unaware of the idea and related information. The flow rate refers to the air flow velocity, while the static pressure refers to the static pressure. We are in the moving air in the compartments of the high-speed train, thus the faster the train moves, the faster the air follows, and the smaller the static pressure becomes. As a result, our ears function similarly to a pressure gauge, detecting variations in time.