Acceleration

His velocity is increasing and becoming unconstant, therefore displaying acceleration.

The picture above displays acceleration, which is the change in velocity over the change in time(a=change in v/change in time). Acceleration is described on a velocity vs time graph. There is no acceleration existing if the velocity time graph contains a horizontal line, meaning that the velocity is constant or zero. In the positive section of the v/t graph, the acceleration is in a positive direction. The acceleration depends on a positive or negative slope. The acceleration speeds up when travelling away from the origin while it slows down when travelling toward it, regardless of being in the negative or positive zone.