Place a Card Over the Open Top of a Glass

question 27

Multiple Choice

Place a card over the open top of a glass filled to the brim with water, and then invert it, as is shown below. Why does the card stay in place? How about when the glass is held sideways?

• A)The weight of the air pushing against the outer surface of the card is much greater than the weight of the water pushing against the inner surface of the card, whether inverted or held sideways.
• B)The adhesive force between the water and the card is greater than the force exerted by the weight of the water from the inside of the glass both in the inverted position and while held sideways.
• C)Inverting the glass with the card in place creates a sufficiently strong vacuum so that the water is not permitted to escape. That vacuum is the same when the glass is held sideways.
• D)The surface tension that was created by putting the card in place is converted to a force of adhesion which exceeds the force exerted by the weight of the water in the glass, whether inverted or held sideways.

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