Make a Cork Stay in the Middle

The Action

Observe a mysteriously behaving cork! Does it stick to the side of the glass, or will it float in the middle? Challenge students to make the cork float in the middle.

Grade Level

Grade 10 - Water Quality

Grade 10 - Science Challenge


Glass (drinking glass)




Fill a glass ½ full of water. Drop the cork in the glass and observe where it floats. Add more water to the glass until the glass is completely full. Now observe where the cork floats.


The trick is to completely fill the glass and have the water just heaping over the top is so that the highest point of the water is in the middle of the glass.

Science Principle

The cork always goes to the highest point of the water. If the glass is not full, the highest point is along the edge of the glass, and it appears that the cork sticks to the edge of the glass. If the glass is heaping full, the highest part is in the middle, and thus the cork floats in the middle.

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