A.1 · 1 · Opening of A.1 Kinematics (before A.1.1)
Motion or rest?
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Hook
You sit on a train at 100 km h⁻¹. A friend on the platform says you are moving. You say you are still. Who is right?
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Which is the better question about motion?
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A passenger is at rest relative to the train. Relative to the ground she is…
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Why is motion relative?
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A cyclist passes a bus stop. Describe her motion relative to two different reference points.
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Summary card
Key points
- • Ask: is position changing with time, from a reference point?
- • Yes: motion. No: rest.
- • Motion is relative, because position is relative.
Key terms
- Reference point :
- where position is measured from
- Motion :
- a change of position with time
- Rest :
- no change of position with time
Common errors
- • Saying "it moves" without a reference point.
- • Thinking rest and motion are absolute.
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