Relative motion

1. When a ball is kicked past a goalpost, the goalpost—which is not in motion—is the reference point for the moving ball. 
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3. For example, when a car is in motion,  the ground is the reference point. In this setting, the ground is seen as not moving relative to the car.
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5. Relative motion is the calculation of the motion of an object with regard to some other moving or stationary object. 
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7. Another example.  A person sitting in an airplane is at zero velocity relative to the airplane, but is moving at the same velocity as the airplane with respect to the ground.
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9. The velocity of an object is the rate of change of its position with respect to a frame of reference, and is a function of time. 
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11. Velocity is equivalent to an object's speed and direction of motion (e.g. 60 km/h to the north). Figure 1.
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13. Whether it's a car moving, a ball being dropped, or the earth moving around the sun, all of these things have their own velocity.
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15. Initial velocity describes how fast an object travels when gravity first applies force on the object. 
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17. On the other hand, the final velocity is a vector quantity that measures the speed and direction of a moving body after it has reached its maximum acceleration.
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19.  If an object starts from rest then it's initial velocity would be zero. Figure 2.
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21. However if it is already in motion then it does have an initial velocity of greater than zero. Figure 2.
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23. Displacement and velocity here.

Figure 1

 

Figure 2

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