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2016 – Prototype Demos - MIT-Harvard Center for Excitonics

Prototype Demonstrations – May 5, 2016

Hot or Really Hot ?:  Two hot plates were prepared, one at moderate temperature (~150F) and the other one at very hot temperature(~250F), with surface thermometers sitting on top of the hot plates. Audiences are asked “if you drop water, which one will evaporate faster?” Most of them think the water drop on the hotter one will evaporate faster. However, the result is counter-intuitive. What happens is that the hotter one generates water vapor below the water drop, lifting up the water drop and separating it from the hot surface. Thus, the water drops can stay for a much longer time, and they wander around without friction.

Understanding these properties is crucial not only for fundamental science where liquids are used as solvents for chemical reactions or media for biological cells, but also in our everyday life in the kitchen and bathroom. Fascinating behaviors of fluids shown in this demo can also be observed at home with a frying pan. This helps us see what’s going on in a microscopic world, where individual molecules are dancing around and colliding with each other.

Molecular Vibration: This demo consists of a series of pendulums connected with springs.  The behavior of the oscillating pendulums mimics the behavior or molecular vibrations.  We used the setup to demonstrate how molecules vibrate in specific patterns or modes, and how a vibrational mode can absorb and store energy if excited at its resonant frequency.  This is how gas molecules in the atmosphere absorb infrared light and cause the greenhouse effect.