RESISTING CHANGE (Inertia)
Students, believe it or not, have an intuitive sense of inertia already. “Heavier” things are tough to get moving. Lighter things…easier. Good demonstrations can get them to adopt the appropriate language to talk about inertia and mass.
We define inertia to be: “an object’s tendency to resist change”
5. Corporal Punishment in Space (weight vs. inertia) |
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 By moving textbooks laterally, we can demonstrate how mass factors into motion, and changing the motion of objects. Holding texts out at arm’s length is difficult on Earth, but on the moon, this task becomes dramatically easier because we have reduced the weight of the books (not the mass, just the weight). However, if we moved the books back and forth, the effort it takes to stop the texts and reverse their direction is actually quite difficult. |
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6. Fast / Slow Pull (it takes time to move) |
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 It does take time time to get objects moving. The Fast / Slow Pull demonstrates the classic “string break” question from the Giancoli text about a heavy mass suspended by a string, and pulled on by a string dangling beneath it. If you pull on the mass quickly, will the supporting string break above the mass, or will the string pulling beneath the mass break? What if you pull on the mass slowly? |
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7. Foucault Pendulum |
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 This famous pendulum demonstrates that the Earth is rotating, while the pendulum maintains is motion. The pendulum does change its motion (due to the string it is hanging on), but it maintains its motion along a steady axis. Our Foucault pendulum is mounted on a turntable “Earth”, and one the turntable is set into motion, we will use appropriate camera angles (one mounted on the turntable, and one to the ceiling) to demonstrate that the Earth rotates beneath the pendulum, but the pendulum continues along its axis of motion. |
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