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Short arm pushes, long arm flings
Age 12 · Physics
When the pivot sits close to a heavy block, a light block far out on the long arm can balance it. If the beam swings, the long tip sweeps a much bigger arc in the same time, so it moves fast enough to throw things far.
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In the picture
- Pivot near one end: splits the beam into a short arm and a long arm
- Big block on the short arm: heavy, but it moves only a little
- Small block at the long tip: light, but it sits far from the pivot
- Arc of the long tip: a much longer path in the same swing, so the tip moves faster
Examples
- On a seesaw, a heavy adult sits close to the middle so a light child at the far end can balance them.
- A trebuchet drops a heavy weight on its short arm, and the long arm flings a stone far across a field.
Key takeaways
- A beam balances when weight times distance from the pivot is equal on both sides.
- The long end travels farther in the same time as the short end, so it moves faster.
Quiz: Short arm pushes, long arm flings (Age 12)
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A heavy block sits close to the pivot and a light block sits far out on the other side. What makes the beam balance?
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When the beam swings, why does the tip of the long arm move faster than the short end?
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When the pivot is close to a heavy block, how far does that heavy block move as the beam swings?
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