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← Measurement of Length and Motion

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Lesson 5 of 9

Has it moved?

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5 min

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Watch a shadow for ten seconds. It does not seem to move. Check again later. It has moved.

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A tree stands fixed beside the road.
Step 1 of 4
  1. A tree stands fixed beside the road.
  2. The bus, at the start.
  3. The bus, later, further from the tree.
  4. Its distance from the tree changed. It has moved.

Position — where a thing is. The shadow's position changed, so it has moved.

Reference point — the thing you compare a position with.

In motion — the position changes compared with the reference point.

At rest — the position does not change compared with the reference point.

Example: a bag sits on a bus seat. Compared with the bus, the bag is . Its distance from the bus does not change. Compared with a tree by the road, the bag is . Its distance from the tree changes.

Try the lab to finish this lesson.