Hi

Just 2 questions

1) My physics teacher said that if I placed a glass of water on a page (on a desk or firm surface), and then pull the page quickly, the glass of water wouldn't move. However, if I pulled the paper slowly, the glass would move along with it.

I dont understand the concept. Which law(s) of motion applies to this scenario?

2) Attach a thin string to a mass-piece and tie it to a bar, letting it hang in mid-air. Tie another thin string to the bottom of the mass-piece. Jerk the bottom string downward quickly.

__________    <--- bar of a table (or anything else)
         |
         |  <--top string
         |
    MASS PIECE
         |
         |  <--bottom string
         |


Observations:
-When the string is pulled quickly (and with a large enough force), the bottom string breaks and the mass-piece remains hanging because of the top string.
-When the string is pulled slowly, the top string snaps and the mass-piece falls to the ground.

How do I explain the observations? I dont understand why pulling the string slowly will be any different to jerking it quickly.

Thanks

Last edited by snoman (2008-03-01 15:26:00)