Heat sensitive pads question

The pads have a thin layer of liquid crystals under a layer of plastic. Liquid crystals are materials that are on the threshold of conditions between liquid and solid. Different liquid crystals react to different stimuli, but these are temperature sensitive.

The color of a material depends on the way the material's molecules respond to light of different wavelengths (colors) and that in turn depends on the structure of the molecules. A piece of red paper has pigments in it whose molecules resonate with (or hum along at) and reflect the frequency of red light and it absorbs the other colors of the spectrum.

The liquid crystals in the pads (and the pigments in the pencils we distribute) are made of molecules whose properties change with temperature in such a way that it changes the way the molecules interact with colored light. When the pads are room temperature, they absorb all the light, and appear black. As they warm to body temperature, the size and shape of the crystals change, and they run through the color series resulting in the beautiful colors.

Light and color have fascinated and confused people for a long time. I have only scratched the surface of this subject here. It is a good one and your question is a good question. Thanks for asking.

What causes friction?

Friction happens when things move against each other. The tiny particles that things are made of, atoms and molecules, push on the particles in something moving across it. This makes them vibrate, or wiggle, and when particles wiggle we call this heat. When something heats up, it takes energy, and the energy has to come from somewhere. (Remember that energy is neither created nor destroyed.) In this case the energy is taken from the motion of the objects, and they have to slow down.

A lot of scientists have tried hard to get rid of friction in their equipment, but sometimes friction is very useful. If there was no friction, a car or bicycle would not be able to start up or slow down. The ground, floor, or whatever you are standing on would be slipperier than ice. Pencils would have to be shaped differently or they would just slide out of your fingers, but that wouldn't matter because without friction, a pencil wouldn't make a mark on paper anyway. It is more fun to think about than to experience, I bet.