The change in position of an object is measured with respect to a reference point and time.
Explanation
An object's motion, and thus any change in its position, is always described relative to something else. This "something else" is typically:
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A Reference Point (or Frame of Reference): This is the fixed location or object from which you are measuring the position of the object in question. The choice of reference point is arbitrary, but crucial for defining and understanding the change in position (displacement). Without a reference point, talking about position is meaningless.
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Time: Motion is defined as the change in position over a duration. The question inherently implies that the change in position is observed over a period.
Examples
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Example 1: A car moving on a road. The car's change in position can be described with respect to a stationary building on the side of the road. As the car moves away from the building, its position changes with respect to that building.
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Example 2: A person walking on a train. Their change in position can be described with respect to their starting seat on the train, or with respect to a fixed point on the ground outside the train. The two descriptions will yield vastly different distances and directions.
Key Concepts
- Position: The location of an object in space relative to a chosen reference point.
- Displacement: The change in position of an object; a vector quantity with both magnitude (distance) and direction.
- Frame of Reference: A coordinate system or perspective from which motion is observed and measured.
