4A: Let’s imagine blood flowing through the aorta, one of the great vessels in our body. At peak velocity, blood may flow at 92 cm/sec (during contraction) or perhaps 60 cm/sec during relaxation. Going from 60 cm/sec to 92 cm/sec in 1 second is a lot different from going from 60 cm/sec to 92 cm/sec in 10 seconds. That difference is acceleration, that is, how quickly the car changes its velocity over time. (When you hear automobile enthusiasts compare the “0 to 60” capabilities of the latest sportscar, they are referring to the acceleration).