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Showing posts from September, 2014

What is Voltage?

Voltage is electric potential energy per unit charge, measured in joules per coulomb ( = volts). It is often referred to as "electric potential", which then must be distinguished from electric potential energy by noting that the "potential" is a "per-unit-charge" quantity. Like mechanical potential energy, the zero of potential can be chosen at any point, so the difference in voltage is the quantity which is physically meaningful. The difference in voltage measured when moving from point A to point B is equal to the work which would have to be done, per unit charge, against the electric field to move the charge from A to B.

What is the Physics Behind Walking on Broken Glass?

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For this demonstration the glass bottles should first be soaked in water to remove any paper labels. An alternative is to use Mason jars. It is best to use fairly large bottles so that the pieces formed will have only a gentle curve to them. When breaking the bottles I place them in a canvas sack and use a hammer, being sure to wear gloves and eye protection. The glass should be broken into fairly small pieces. The bed for the glass may be made from half-inch-thick plywood framed by pieces of 2"34” wood. Once the glass has been poured into the bed it should be spread out to a uniform depth. Any piece that has a right-angled bend in it, where the sidewall of the bottle meets the base, is moved to the edges of the bed so that only relatively flat pieces of glass are included in the center of the bed where the walking takes place. As an extra precaution, I cover the glass with a cloth and then use a large cast iron skillet to pound the surface firmly. This ensures no points of glas…