# Physics - Acceleration

Today we continue describing motion by talking about acceleration. Acceleration is the rate of change of velocity over time. We most often think of acceleration when thinking of cars and how fast they can go. However, acceleration can be slowing down in addition to speeding up as it's about the rate of change and not the direction of movement. Velocity is not as important as the change in velocity per unit time, which is known as average acceleration. Why is the change more important than velocity? Think of this, you are in a car going 60 mph and it changes to 0 mph in 1 second. As Professor Steven Pollock notes in his lecture, this would most likely mean you were in a wreck and that could really matter if you were in the car! Of course, this is all describing constant acceleration, which is simple to calculate because no matter if you are slowing down or speeding up it's in a straight line fashion. However, sometimes acceleration is not at a constant speed and in today's free Physics 1 video on Acceleration, you'll learn how to calculate this. Next time you get in a car, think about acceleration and you'll see the trip in a whole new light!