What is the fundamental difference in how cyclic pitch and collective pitch affect the rotor disk?

The fundamental difference is that collective pitch changes the pitch angle of all rotor blades equally and simultaneously, while cyclic pitch changes the pitch angle of each rotor blade differently as it rotates. Collective pitch control allows the pilot to uniformly increase or decrease the angle of attack of all the rotor blades. Increasing collective pitch increases the lift produced by all the blades, causing the helicopter to ascend (or preventing it from descending). Decreasing collective pitch decreases the lift produced by all blades, causing the helicopter to descend. Cyclic pitch control, on the other hand, changes the pitch of each blade as it rotates through its cycle. The cyclic control allows the pilot to selectively increase the lift on one side of the rotor disk and decrease the lift on the opposite side. This difference in lift across the rotor disk tilts the rotor disk, causing the helicopter to move in the direction of the tilt. Tilting the rotor disk forward causes the helicopter to move forward; tilting it to the left causes the helicopter to move left, and so on. Therefore, collective pitch controls vertical movement (ascent and descent), while cyclic pitch controls horizontal movement (forward, backward, and sideways).