Showing posts with label science store. Show all posts
Showing posts with label science store. Show all posts

8/19/2009

Tensile Intergrity Sphere

Hanging high above the center of the MOSI Grand Lobby is a very large and odd-looking sphere composed of yellow rods and wire. If you spend a few moments and really look at the sphere you will see that none of the yellow rods that compose the sphere are touching each other. This neat bit of science is known as a Tensile Integrity Sphere.

How does it work?:
A tensile integrity sphere or tensegrity sphere is a structure that utilizes synergy of components in balanced compression and tension for structural support.

Compression is stress or force applied to materials resulting in their compaction. In the case of this sphere the yellow rods are under compression. Tension is a force that pulls upon an object using strings or wires and is the opposite of compression. The wires in the tensegrity sphere are in tension. Synergy is a situation where different entities or forces cooperate advantageously for a final outcome, in our case keeping the sphere round without external supports. Utilizing the forces of compression and tension in synergy this 130 pound sphere is entirely self-supporting and hangs from the ceiling with just a few strong cables that support the weight of the entire sphere.

Tensegrity:
The concept of tensegrity was popularized by R. Buckminster Fuller and Kenneth Snelson at Black Mountain College in the 1940's. Building upon an early design of a self supporting sphere structure used as a planetarium in Germany, Fuller and Snelson explored concepts of tensegrity.
The term 'geodesic' was coined by Fuller and applied to structures that could be incredibly light for their size when compression and tension were used in balance to create structures that were self supporting. Within a geodesic dome, no internal supports are required. Just imagine your house without any need for walls! Geodesic structures had potential to be spacious, light weight, strong and inexpensive to produce.
"Ability to respond as a system means that local stresses are being uniformly transmitted throughout the structure, and uniformly absorbed by every part of it. The system's symmetry is not deformed: the system expands as a whole or contracts as a whole. This is not the behavior we are used to in any structures of our previous experiences. The compression members do not behave like conventional engineering beams... Ordinary beams deflect locally. The tensegrity "beam" does not act independently of "the whole building" which contracts only symmetrically when the beam is loaded. The tensegrity system is synergetic - a behavior of the whole unpredicted by the behavior of the parts" -R. Buckminster Fuller. Synergetics: explorations in the geometry of thinking. New York, Macmillan, 1975
The story of our sphere:
In November of 2000 the museum was approached by Richard 'Dick' Avery who had an interesting proposal. He wanted to build an enormous tensegrity sphere for the museum to display. Dick had found a book on R. Buckminster Fuller in the Science Store at MOSI some time before and had become enamored of the concepts of tenesgrity. At home in Sun City Center, Dick had already built a few tenesgrity spheres and offered to build one for MOSI.

Dick spent 107 hours constructing the sphere in January and February of 2001 and shortly after it was hung in our grand lobby. It was quite a sight to see a gigantic yellow sphere sitting on the floor of the lobby and several exhibit technicians carefully considering how they were going to hoist the monster shape into place. After a few hours, the great tensegrity sphere hung above our lobby and hangs there to this day. Mr. Avery passed away several years ago, but his creation still looms larger than life over hundreds of thousands of people each year.

8/12/2009

Funky Science: Lava lamps

The Science Store at MOSI has a really huge lava lamp on display and lots of smaller lava lamps for sale right now. The large lava lamp is really awesome to watch so I thought perhaps we should talk about the science of lava lamps!

Lava Lamps: Lava lamps, also known as liquid motion lamps, have been around since the 60's. They are very cool to watch but there are some neat principles of science in action.

So how does a liquid motion lamp work? Liquid motion lamps require the use of two insoluble, near equal density liquids and a heat source used for adjusting the density of the liquids. Now lets break that down into bite sized pieces.

Liquids: One liquid forms the slow moving blobs, like in the picture, we will call this Red. The other liquid allows the blobs to float about, we'll call this liquid Purple.
  • These liquids must be immiscible, or mutually insoluble. This means that neither liquid will dissolve the other like oil and water and that Red and Purple will remain separate.

  • These liquids must be of a nearly equal density.

When turned off, liquid motion lamps appear to have two distinct layers of liquids . One is just slightly more dense than the other and lays on the bottom of the lamp. In our case the Red liquid is slightly more dense than the Purple liquid. Being more dense causes the Red liquid to sink to the bottom.

Heat: The heat source in a liquid motion lamp is generally a light bulb or lamp. As you likely know, light bulbs can get pretty hot when they have been turned on. When the lamp is turned on it heats up the slightly more dense Red liquid at the bottom of the lamp.

Changing the temperature of a compound is an easy way to change density. When a compound is heated the molocules in the compound spread apart making it less dense. As the density decreases, the compond become lighter and will rise above heavier, more dense compounds. For example, think of air: hot air rises and cold air sinks. Heated air becomes less dense and becomes "lighter" which causes it to rise above the more dense, "heavier" cool air.

Much like hot air, the Red liquid at the bottom of the lamp will become less dense as it is heated. This makes the Red liquid "lighter" and it begins to rise in blobs through the Purple liquid.

As they rise through the Purple liquid and away from the heat source, the Red blobs lose heat. This causes the molecules in the Red liquid to move closer together and this increases the density of the Red liquid. The Red blobs are become more dense than the Purple liquid and sink back to the bottom. At the bottom the Red liquid is warmed up again and the process repeats until you turn off the lamp and all the Red liquid cools down.

This really neat Wiki How article shows you how to make a liquid motion lamp with household items and no heat! Be a scientist at home!