ok, I'm gonna take a stab at it but I'm having a hard time understanding your question:
The reason acceleration is not the change in speed per unit time is because of the speed versus velocity distinction. Speed is the distance traveled in a certain amount of time. Velocity is the displacement from an initial position in a certain amount of time.
A rectangular track has dimensions of 100 meters by 50 meters. If you were to run around this track in 10 minutes, you would travel a total distance of 100+50+100+50 meters. This means that your average speed was 30 meters per minute. However, your displacement is zero when you return to your original position. While you have moved, you have not made it anywhere. Your average velocity would be zero.
The key point here is that velocity is a physics term that describes both rate of change in somethings position per unit time, AND the direction of that change. Importantly, acceleration is DEFINED as the rate of change in velocity per unit time. Acceleration, therefore, implies direction since velocity has a direction (they are both vectors).
In order to determine something's velocity, you just need to know how many units of distance are traveled in a single line each second/minute/unit time. If something is changing directions continuously, its velocity, by definition, is also changing with each change in direction.
· 8 years ago