Post by cwdlaw223 on Jan 14, 2013 14:40:18 GMT -5
VELOCITY -
Suppose a car leaves Chicago and travels for 4 hours with an average speed of 50 miles/hour. Where will it be at the end of this time?
(Speed (i.e., how fast) is a scalar quantity (magnitude). Velcoity is a vector quantity (magnitude and direction).
Who knows? The car could be 200 miles (= 50 mi/hr x 4 hr) north of Chicago, it could be 200 miles west - or any other direction. It could even be back in Chicago (if it went 2 hours west, then 2 hours east, for instance)! It could be anywhere within a 200 mile radius of Chicago. That is not a very precise description of the car's motion!
Clearly, speed is not adequate to describe the motion of an object. You need to know its speed and direction.
Velocity is the kinematic concept that describes an objects speed and its direction.
(a) Change in Velocity -
It is important that you be able to recognize when the velocity of an object is changing. Since velocity is speed and direction, the velocity of an object changes if:
it speeds up.
it slows down.
it changes direction.
Note that the velocity of an object can change, even if its speed remains constant. For instance, when a car is going around a curve (like an entrance ramp on an interstate), it is accelerating - even if the speed of the car stays the same. Velocity changes when either speed or direction changes.
ACCELERATION -
Acceleration is the rate at which velocity changes. In other words, knowing the acceleration of an object tells you how fast the velocity of the object is changing.
Since velocity is the rate at which position changes, and acceleration is the rate at which velocity changes, acceleration is a "rate of a rate".
students often get the misconception that "acceleration is a change in velocity". NO!! Acceleration is the rate at which the velocity changes - there's an important difference!
To say that "acceleration is a change in velocity" is like saying "velocity is a change in position" (This does sound silly, doesn't it?).
Velocity tells you how fast a position is changing.
Acceleration tells you how fast velocity is changing.
Acceleration is not a change in velocity (it's the RATE that velocity changes).
It is very important to notice that acceleration is defined in terms of a change in velocity - not speed.
Suppose a car leaves Chicago and travels for 4 hours with an average speed of 50 miles/hour. Where will it be at the end of this time?
(Speed (i.e., how fast) is a scalar quantity (magnitude). Velcoity is a vector quantity (magnitude and direction).
Who knows? The car could be 200 miles (= 50 mi/hr x 4 hr) north of Chicago, it could be 200 miles west - or any other direction. It could even be back in Chicago (if it went 2 hours west, then 2 hours east, for instance)! It could be anywhere within a 200 mile radius of Chicago. That is not a very precise description of the car's motion!
Clearly, speed is not adequate to describe the motion of an object. You need to know its speed and direction.
Velocity is the kinematic concept that describes an objects speed and its direction.
(a) Change in Velocity -
It is important that you be able to recognize when the velocity of an object is changing. Since velocity is speed and direction, the velocity of an object changes if:
it speeds up.
it slows down.
it changes direction.
Note that the velocity of an object can change, even if its speed remains constant. For instance, when a car is going around a curve (like an entrance ramp on an interstate), it is accelerating - even if the speed of the car stays the same. Velocity changes when either speed or direction changes.
ACCELERATION -
Acceleration is the rate at which velocity changes. In other words, knowing the acceleration of an object tells you how fast the velocity of the object is changing.
Since velocity is the rate at which position changes, and acceleration is the rate at which velocity changes, acceleration is a "rate of a rate".
students often get the misconception that "acceleration is a change in velocity". NO!! Acceleration is the rate at which the velocity changes - there's an important difference!
To say that "acceleration is a change in velocity" is like saying "velocity is a change in position" (This does sound silly, doesn't it?).
Velocity tells you how fast a position is changing.
Acceleration tells you how fast velocity is changing.
Acceleration is not a change in velocity (it's the RATE that velocity changes).
It is very important to notice that acceleration is defined in terms of a change in velocity - not speed.