When does compression begin with the motor?

The correct answer indicates that compression begins at full speed. In the context of a train's motor or engine operation, full speed is typically associated with the point at which the engine has reached an optimal performance level, allowing for the most efficient compression of air within the cylinders. During this phase, the engine components move at their maximum velocity, generating the necessary pressure for effective combustion and power generation.

It is important to note that while engines may have varying behaviors at low and medium speeds, complete compression is not achieved until the engine is functioning at its designed full speed. The dynamics of engine operation are such that there are specific RPM (revolutions per minute) ranges where the performance is maximized, which directly correlates to the timing and effectiveness of the compression stroke.

In summary, compression at full speed ensures that the engine functions as intended, enabling it to produce the required thrust and efficiency for train operations.