The graph of a pure tone that consists of only a single frequency produces a sine wave. In the case of a 100 Hz tone, one cycle of the waveform is completed in 10 milliseconds. Since there are 1000 milliseconds in a second, 100 cycles of the tone will be completed in one second.
A single cycle of the sine wave represents one back-and-forth movement. When the tone is sent to a speaker, the positive peak will move the speaker cone in one direction and the negative peak will move the cone in the opposite direction.