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Introducation to Atoms and Energy
What do these have in common: gum, cellophane tape, glue, geckos?
What explains the ability of something to stick to clean, smooth glass? Here are some incorrect explanations that have been proposed:
Sticky material can grab onto rough places that every substance has.
Sticky material has special molecules that are very sticky.
Static cling—sticky material has atoms with strong charges are attracted to atoms of glass.
Sticky material has a thin layer of water that sticks to the glass.
Sticky material penetrates a bit into the glass.
Sticky material has atomic-sized suction cups that create a partial vacuum.
The explanation is that all atoms stick with an attractive force, if they get close enough. If all atoms stick, then why doesn't everything stick to everything else? The answer is surprising: most of the time when two objects touch, very few atoms are close enough to stick. Surface roughness, contaminants, water, and air get in the way and keep most atoms from getting close enough to attract.
This activity answers questions about how things stick by looking into the forces between atoms and their energy. The answers come from applying Newton's Laws to atoms.
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Answer
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They all stick to many surfaces.
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How gum works
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Gum is not rigid, so it can flow onto the glass. This lets its atoms get close enough to glass atoms to be attracted to them.
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How tape works
Sticky tape has a thin sticky surface that is not rigid, so it can flow onto the glass. Like gum, this lets its atoms get close enough to glass atoms to be attracted to them.
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How glue works
Glues start as a liquid that can flow over a surface and make atom-to-atom contact before they turn solid.
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How geckos stick
Geckos have special feet with billions of rods that can adjust to any surface roughness.
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