Wednesday, 9 December 2015

A Big Tall Glass of Common Sense.


The British tabloid press are at it again. Virtually every tabloid paper in the UK has reported on this piece of footage from Honduras breakfast TV show First Edition over the last 24 hours.

Take a look.


So is this "chilling" or paranormal in any sense?

No. Not in my opinion. What we are seeing here is the natural outcome of a glass resting on a glass table with a speck of moisture , or even moist air trapped underneath it. The coefficient of static friction being very small between two glass surfaces even without the presence of water or moist air.

Arnold Anderson, retired professor of frictional forces explains the effect:
"When a wet glass is placed on a smooth surface, a ring of water first
makes a seal around the bottom edge of the glass. Then, as the glass
continues toward the countertop, air that is under the glass bottom is
compressed. Under ideal conditions, this small volume of pressurized air
is able to support the weight of the glass. The water around the bottom
edge of the glass functions as a seal to prevent the air from escaping.
For a short time, the glass is floating on the surface water, and moves
with almost no friction. A different, but related behavior is possible
with a container that has a very smooth, flat bottom. Here, the water can
not escape quickly, and temporarily supports the glass on a squeeze film
of water alone. This is much like an ice skate, which melts the ice under the blade, so
the skater glides freely on a thin film of water. The first case is like
a hovercraft, where a large fan pressurizes the air under the craft so it
can move freely over water or even smooth land. Technically, the glass uses what is called a 'squeeze film' bearing to temporarily support the glass. Hovercraft are supported by 'externally pressurized' bearings. Ice skates employ 'self-lubricating' bearings. These are all ways to reduce friction, using lubrication."
 So what sets the glass moving? Could be one of two things, or a combination of the two, heat from the studio lights causing the fluid to expand, or the presenter disturbing the air around the glass and setting it in motion. Notice that the glass begins to move as the Presenter moves his hand past it, the initial movement is very slow and the glass speeds up as it moves towards the middle of the table. It finally stops when the moisture is exhausted. It would take very little force to get the glass moving as the static coefficient, the resistance against sliding, is so small.

Examination of the surface doesn't immediately reveal the presence of liquid.  But all that is needed here is moist air, or condensation on the outside of the glass.

More tabloid stupidity then. As mentioned in a previous post, I'm not linking to any of the stories, click-bait shouldn't be encouraged.