Mechanics

1D50.40: Pail of Water


Description: As a bucket or cup of water is spun in a circle, the water does not fall out. This is because the string (or platform, in the case of the stiff bar) provides a centripetal force, while the inertia of the cup of water (Newton's first law) causes an apparent "centrifugal force", which keeps the water in the bucket.

Note: If you go too slow, the water will fall out.

Equipment: Setup Procedure:
  1. Check to make sure strings are securely attached.
  2. Can fill the bottle/cup ahead of time, or leave for professor to fill in class. Ask what is preferred.
Demonstration Procedure:
  1. Carefully start swinging the water-filled bucket.
  2. Get it going as fast as possible, as soon as possible.
  3. When stopping, try to stop gradually so as to avoid spilling water all over the floor. You have to use some physics intuition to get the hang of this!
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