What is the function of a tool that controls when the main motor receives power?

The function of a tool that controls when the main motor receives power is accurately represented by the clutch. A clutch serves as a mechanism that engages or disengages the motor from the operational load, allowing for control over when power is transmitted to the motor. When the clutch is engaged, it connects the power source to the motor, enabling operation. Conversely, when disengaged, it interrupts the flow of power, effectively stopping the motor's function without turning off the entire electrical system. This functionality is critical in applications where precise control over motor operation timing is necessary, such as in machinery that must start and stop frequently or operate at variable speeds.

Other options do provide some level of control but do not precisely match this specific function. A trigger initiates action typically in tools like drills, a switch simply turns the electrical supply on or off without the engagement modulation provided by a clutch, and a power adapter converts electrical power but does not control the timing of power delivery to a motor.