Relative Motion
When we discuss the motion of an object, we are really talking about the motion of that object relative to some other object. In the video at the right, after the plane lands, it has a velocity of zero RELATIVE TO THE AIRCRAFT CARRIER. However, the plane does NOT have a velocity of zero relative to the surface of the earth. |
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Most often, we will talk about the motion of an object relative to the surface of the earth. Thus, when we say a car is moving at 65 km/hr, we generally mean it is moving at 65 km/hr RELATIVE TO THE SURFACE OF THE EARTH. |