2008 HS Photo Contest Pictures

2008 AAPT High School Physics Photo Contest
Winner's Showcase

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First Place - Contrived

Title: Paperclip Peculiarity
Student: Shilpa Hampole
School: Notre Dame High School, San Jose, CA
Teacher: Bill Whitney

This photo was contrived by placing a paperclip on the surface of some water in a bowl. The light source is a window with blinds and bright light coming through. The paper clip is not actually “floating,” rather it is supported by surface tension. Unlike a cork that floats back up to the surface when it is pushed underneath, a paperclip will sink unless the surface tension is strong enough to support it. Surface tension is the term that describes the rubbery “skin”-like layer that is formed on the surface of water where molecules attract each other and hold together tightly. This attraction, which is called intermolecular force, is responsible for surface tension. Water, a polar substance, has both positive and negative molecules that attract. The molecules attract each other in all directions except at the very surface of the water where the molecules are attracted across the surface and inward. This causes the water to become spherical. So, unless enough pressure is put on the paperclip to push the water out of its spherical shape, the paperclip will not be able to stretch the water’s surface enough to slip through and sink. The pattern from the blinds together with the curvature and bending of the water shows the depression in the water around the paperclip. This demonstrates the rubbery skin-like surface layer that holds up an object when the bond between the positive and negative molecules is strong enough.