What does the term "wheel slip" refer to?

The term "wheel slip" specifically refers to a situation where the wheels of a train lose traction, leading them to spin without effectively moving the train forward. This phenomenon is most commonly encountered when there is insufficient friction between the wheels and the tracks, which may occur in conditions such as wet or icy rails, or when excessive power is applied during acceleration.

When wheel slip happens, the train is unable to gain the necessary traction to move forward efficiently, which can impede the train’s overall performance and safety. It is critical for railway operations to monitor and manage wheel slip, as prolonged wheel slip can lead to wheel damage and degrade track conditions.

In contrast, the other options pertain to unrelated mechanical issues. For instance, tightly secured wheels or misaligned wheels do not directly relate to the loss of traction, and overheating brakes involve a different set of mechanical failures that do not produce wheel slip. Understanding the specific mechanics of wheel slip is essential for operating and maintaining rail systems effectively.