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Tom Barner
Mar 15, 1992, 9:06:41 PM3/15/92
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BROWN BAG #4
WHERE DOES IT FLOAT?
.
When the glass is half filled with water, the circumference of the meniscus is
the highest level.(Meniscus is a good word to have the children look up if they
haven't heard it
before>) This is caused by the adhesive forces between the glass molecules and
the water molecules. As a result of this high level the object moves to that
level.
.
When the glass is filled to the brim with water, the cohesive forces between
the water molecules and the surface
tension form a film on the surface of the water, making it
possible to fill the glass more than full. (If you have done
the Life at the Surface Brown Bag experiment, this may seem
familiar and children may make some connections here) The
highest level of the meniscus is at the center of the glass now and that is
where the object floats. Floating objects tend to float at the highest spots of
the meniscus.
.
Some questions for after the experiment:
Why is the cork moving towards and sticking to the side of the glass when it is
half full?
.
Where is the water level the highest in the glass with the glass half filled?
(This is a good place to do some metric
measurement.)
.
Why does the cork float in the center of the full glass?
.
Where is the water level the highest in the full glass?
(another chance to measure)
.
Why can the glass be filled to more than full without overflowing?
.
Be sure to allow children to explain any other experiments that they have done
with the glass of water and the object.
.
This is an easy experiment to set up and do. It is not
labor intensive in collecting the equipment (a gift for just after the
vacation) but it is an interesting one in terms of the explanation and the
discussion. Enjoy.
WHERE DOES IT FLOAT?
.
When the glass is half filled with water, the circumference of the meniscus is
the highest level.(Meniscus is a good word to have the children look up if they
haven't heard it
before>) This is caused by the adhesive forces between the glass molecules and
the water molecules. As a result of this high level the object moves to that
level.
.
When the glass is filled to the brim with water, the cohesive forces between
the water molecules and the surface
tension form a film on the surface of the water, making it
possible to fill the glass more than full. (If you have done
the Life at the Surface Brown Bag experiment, this may seem
familiar and children may make some connections here) The
highest level of the meniscus is at the center of the glass now and that is
where the object floats. Floating objects tend to float at the highest spots of
the meniscus.
.
Some questions for after the experiment:
Why is the cork moving towards and sticking to the side of the glass when it is
half full?
.
Where is the water level the highest in the glass with the glass half filled?
(This is a good place to do some metric
measurement.)
.
Why does the cork float in the center of the full glass?
.
Where is the water level the highest in the full glass?
(another chance to measure)
.
Why can the glass be filled to more than full without overflowing?
.
Be sure to allow children to explain any other experiments that they have done
with the glass of water and the object.
.
This is an easy experiment to set up and do. It is not
labor intensive in collecting the equipment (a gift for just after the
vacation) but it is an interesting one in terms of the explanation and the
discussion. Enjoy.
--
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