MadSci Network: Physics

Re: An experiment using different sizes of steel marbles- (balls)

Date: Fri Feb 9 17:18:23 2001
Posted By: Renafaye Norby, Faculty, Science Education, Black Hills State Univ.
Area of science: Physics
ID: 980193401.Ph

      This idea is similar to the experiment Galileo designed which showed 
that if you drop 2 objects off the Leaning Tower of Pisa, even if they have 
different weights they will hit the ground at the same time (barring air 
resistance) because the acceleration due to gravity is a constant. Dropping 
different sizes of steel balls into a clear container of water (at 
different times) would be interesting because it would show that although 
they hit the water after the same length of time , they splash out 
different amounts of water because they have different momenta (plural of 
momentum) (mass times velocity) when they hit the water. If dropped from 
the same height, their velocity will be the same when they hit the water, 
but the momentum is different because the mass (or weight) is different. A 
similar and less messy experiment is to roll the balls down two different 
tracks (you can make tracks out of angle iron if you can cut the angle iron 
to a desired length) and have each ball strike an identical piece (both 
have same size and same weight) of wood (or soap, or anything that will 
slide with a small amount of friction. Dry ice (frozen Carbon Dioxide) 
would have a small amount of friction, but it would be hard to keep 
identical blocks of dry ice since the mass and size are changing 
continuously). The wood struck by the large ball should move farther, which 
again shows that even though the balls have the same velocity, they have 
different momenta, and the larger momentum will make the block of wood move 
farther on a horizontal surface.

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